improved biomass cooking stove for household use - (PDF, 101 mb ...

Forest Products Research Division 

Royal Forest Department 

Ministry of Agriculture and Coo~perativt's 

IMPROVED BIOMASS 

COOKING STOVE 

FOR HOUSEHOLD USE 

Submitted to the 

National Energy Administration 

Ministry of Science, Technology and Energy 

Under the 

Renewable Nonconventional Enu.rgy Protect 

Royal Thai Government 

U.S. Agen~cy (or International Development 

\~

"Household development in any soc-ety 

can only be achieved when the most iLaportant 

part of the kitchen, the ciokstove, has also 

been improved."

ACKNOWLEDGEMENTS 

I wish to express my appreciaticn to USAID/Thailand, to the Natio:lal 

Energy Administration and Department of Technical and Economic Cooperation 

for their support and for providing a timely opportunity to prove the wood 

energy conservation case In rural application. The Royal Forest Department 

responded eagerly to the request for project personnel and facilities needed 

for implementation. 

I am obliged to Mr. Suthi Harnsongkram, the Director of Forest Products 

Research, who had kindly helped in the execution of the project plan in his 

capacity as the Department's Director General. 

Acknowledgements are due Miss Pojanee Jongjitirat of KMIT for the 

preparation of the main part of this final report and for helping with the 

stove's promotional training; Mr. Banyat Srisom for the final improved stove's 

technical drawings, development of produztion technique and quality control 

for improved designs, and helping with the stove's promotional training; 

Mr. Piroj Uttarapong of Kasetsart University for assisting in test data 

compilation, stove cataloguing, and promotional training. 

Mr. Arkom Vejsupasook. the component assistant, Mr. Songdham Jaikwang, 

and Miss Malee Rungsrisawadth, project officers, were indispensable for the 

day-to-day project operation, by conducting the experiment and collection of 

data, commissioning the improved stove's production, and organizing of 

promotional training programs. 

Personally, I wish to extend my special thanks to Mr. Sompongse Chantavorapap, 

the project manager, and Mr. Minta a Silawatshananai, the USAID 

project officer, for their unfailing assistance whenever problems arose. 

I am also grateful to my research colleaques whose names are all listed 

in the Annex for their invaluable contribution to the success of this project. 

Finally, credit is given to secretarial and the editorial staff of the 

Office of Project Support who patiently strived for a quality final report. 

Aroon Chomcharn 

Component Leader 

Stove Improvement Component 

Royal Forest Department

CONTENTS 

Page 

EXECUTIVE SUMMARY ...................................................... 11 

List of Tables .......................................................... 17 

List of Figures ......................................... :.............. 21 

Terms and Abbreviations ............................................... 25 

CHAPTER 1 INTRODUCTION 

A. The Project ........................................... 31 

B. Historical Background ................................. 32 

C, Statement of the Problem ............................... 34 

D. Objectives of the Study ............................... 36 

E. Potential Benefits for Rural Development .............. 37 

F. Scope of Work ......................................... 37 

CHAPTER 2 REVIEW OF LITERATURE 

A. Stove Construction and Design ......................... 43 

B. Standard Methods of Testing Stove Performance ......... 48 

C. Factors Affecting Stove Performance ................... 51 

D. Conclusion ............................................ 53 

C1APTER 3 PLAN AND DESIGN OF THE PROJECT 

A. Laboratory and Facility Set Up ........................ 57 

3. Collection of Existing Local Stoves ................ 57 

C. Investigation of Existing Stove Performance ........... 58 

D. Analysis of Stove Physical Factors ..................... 58 

E. Development of Improved Prototype ..................... 58 

F. Testing of Prototype and Remodif.cation ............... 58 

G. Production of Developed Stoves ........................ 59 

H. Field Promotion of Developed Stoves ................... 59 

CHAPTER 4 EXPERIMENTAL TECHNIQUES AND PROCEDURES 

A. Fuel Type and Preparation .............................. 63 

B. Tests of Existing Thai Cooking Stoves ................. 64

CONTENTS (continued) 

C. Test for the Effect of Internal Variable on 

the Charcoal Bucket Stove ............................ 

D. Test for the Effect of External Variables on 

the Charcoal Bucket Stove ............................ 

E. Test for the Effect of Variables on the 

'Non-chimneyed Wood Stove ............................. 

F. Test for the Effect of External Variables on 

the Non-chimneyed Wood Stove ......................... 

G. Test for the Effect of Internal Variables on 

CIimneyed Wood Stove ................................. 

H. Test for the Effect of Internal Variables on 

Chimneyed Rice Husk Stove ............................ 

I. Test for the Effect of Internal Variables on 

Non-chimneyed Rice Husk Stove ........................ 

Page 

J. Development of Improved Stove Prototype ......... 04... 75 

CHAPTER 5 ANALYSIS OF RESULTS AND DISCUSSION 

A. Physical Structure of Commercial Stoves .............. 79 

B. Terminology .......................................... 

C. Performance of Commercial Stoves Tested ............... 85 

D. 

The Effect of Internal and External Variables ........ 99 

CHAPTER 6 THEORETICAL,ANALYSIS OF CHARCOAL STOVE 

A. Mathematical Model of the Bucket Stoves 

66 

68 

70 

71 

72 

73 

73 

85 

............. 135 

B. Evaluation of Parameters ............................. 143 

C. Model Application .................................... 144 

D. Discussion and Evaluation ............................ 162 

CHAPTER 7 STOVE MODELS DEVELOPED 

A. Improved Stove's Terminology ......................... 167 

B. Improved Charcoal Stove Model "RFD-1"................ 173 

C. Improved Non-chimneyed Wood Stove Model "RFD-2 " ........ 175 

D. Improved Chimney Wood Stov . .......................... 180 

E. Improved Non-chimneyed Rice Husk Stove ............... 186 

F. Improved Chimneyed Rice Husk Stove Model "RFD-3"....... 187

CONTENTS (continued) 

CHAPTER 8 IMPROVED STOVE DESIGNS AND PRODUCTION 

Page 

A. Technical Drawings of Improved Stove .................. 197 

B. Construction Instructions ............................ 197 

C. A Mass Production Scheme to Make Charcoal and 

Wood Stoves Using the Hydraulic Press ................ 209 

CHAPTER 9 IMPROVED STOVE PROMOTION 

A. Overall Target of Stove Promotion .................... 213 

B. Creation of Public Awareness ......................... 215 

C. Introduction/Training on Efficient Stoves ............ 216 

D. Introduction and Distribution of Sample Stove 

to Hnusehold Users ................................... 229 

E. Organization of Stove Manufacturers to Produce 229 

Improved Design Stoves .............................. 

CHAPTER 10 CONCLUSIONS.......................................237 

CHAPTER 11 RECOMMENDATIONS . ................................... 241 

ANNEXES 

I. 

Commercial Charcoal Bucket Stove Investigated ......... 245 

II. Commercial and User Built Wood Stove Without 

Chiminey Investigated ................................. 285 

III. Commercial Wood Stove With Chimney Investigated ...... 303 

IV. Commercial Rice Husk Stove With Chimney 

Investigated ......................................... 309 

V. List of Staff and Personnel for Stove Improvement 

Component ............................................ 317 

REFERENCES .........................................................321

EXECUTIVE SUMMARY 

Energy for household cooking in Thailand depends largely on biomass 

mainly in the form of wood and charcoal. The annual consumption of both 

fuels in terms of solid wood is approximately 40 million cubic meters, with 

in estimated value of well over 7.5 billion baht. If this quantity of 

wood fuel were to be provided by commercial fuels such as kerosen LPG and 

LNG, the national spending on such imports would be at least three times 

higher. Furthermore, many problems would exist both with effectively 

distributing these forms of energy to rural areas, as well as with its prohibitive 

cost. 

Statistics on wood consumption of the country reveal that the use of 

wood for fuel is approximately 75-80% of all uses (with such purposes as 

construction and industrial applications comprising the remainder). This 

consumption ratic indicates that the country's dependence on wood fuel is 

likely to persist for a long time to come. 

The present scarcity of fuelwood has already appeared in many areas 

of the country. This will occur more frequently as the natural forest 

diminishes and the population increases. In order to correct this problem, 

in addition to planting morc fast-growing species of trees, conservation 

through the improvement of inefficient cooking stoves is necessary. As 

a cnnsequeD-e the Cooking Stove Improvement for Household Use Project was 

launched. 

The objectives of the project were: 

a) to investigate the performance of existing stoves currently 

used in Thailand, 

b) to make necessary improvements on each type of stove (charcoal, 

wood, and agriresidue) for better fuel efficiency and ease of 

operation, 

c) to establish improved stove production techniques suitable 

for small-scale rural industries, 

d) to disseminate information, technology and/or improved 

hardware to stove users, manufacturers, and the general 

public, and 

e) to increase the number of trained personnel and institutional 

research facilities for future campaigns investigating 

efficient biomass cooking stoves. 

This project component was operated by the Forent Products Research 

Division of the Royal Forestry Department. The operation phase was 

started in March 1982 and ended in September 1984. Activities undertaken 

included collection and selection of commercial stoves, stove development 

to yield better design, prototype testing, improved stove production and 

fabrication, and promotion of the improved final models. 

11

Accomplishments can be summarized as follows: 

1) The performance of household cooking stoves in Thailand 

(both commercial and user-built models) was investigated. 

2) Based on the heat utilization efficiency (HU) rating under 

the same test standard, it was found that the average HU's 

for LPG, pressurized kerosene, charcoal bucket, nonchimneyed 

wood, chimneyed wood, nonchimneyed rice husk, and chimneyed 

rice husk stoves were 46, 48, 27, 20, 12, 16, and 5% respectively. 

3) The improvements on the five generic types of biomass stoves 

mentioned above have resulted in HU increases of 26% for 

chqrcoal, 35% for nonchimneyed wood, 58% for chimneyed wood, 

20% for nonchimneyed rice husk, and 100% for chimneyed rice 

husk stoves as compared with the average existing models. 

4) In addition to the HU increase (indicating the net increase 

in work output per unit fuel input), certain stove featurewere 

also improved -- particularly the stove rim design to 

accommodate various sizes of pots and pans, fire-resistant 

characteristics of pottery liners for charcoal and wood 

stoves, and increases of their service lives. 

5) A better clay raw material for pottery liner stoves was 

identified and a production technique suitable for rural 

industries developed. A trial production by village stove 

makers employing this technique was successful. 2000 charcoal 

and 1200 wood stoves of acceptable quality were obtained 

with good production precision. 

6) The component conducted nine improved stove training courses 

for concerned rural government officials and rural stove 

users. The reception for the improved models (particularly 

charcoal and nonchimneyed wood stoves) was very encouraging. 

The reception for rice husk stoves was also enthusiastic, 

but was restricted to a few rural areas only. 

7) During the trial promotion, approximately 1500 charcoal, 

800 nonchimneyed wood, 150 nonchimneyed rice husk, and 50 

chimneyed rice husk stoves were distributed to trainees, 

to interested government and private organizations, and 

to individual users upon request. 

8) As a result of the project implementation, a modest stove 

laboratory, adequately equipped with basic facilities for 

future work, was established at RFD. 

12

CONCLUSIONS 

As a result of the implementation of the Improved Biomass Cooking Stove 

Component, many activities and achievements took place. Accomplishments can 

be described as follows: 

1. As a part of institution strengthening, the component has succeeded in 

establishing a cooking stove testing laboratory at the Forest Products 

Research Division, Royal Forest Department. Thrcugh project funding, the 

laboratory was equipped with invaluable, basic test instruments and 

facilities--including a microcomputer system for future applications. 

2. Long-term training of project personnel to increase their fLcure 

capabilities was minimum bccause time was short (30 months) and they were 

needed on site to carry out project tasks. Therefore, all technical personnel 

were indispensable for project implementation. They could not be spared for 

long term training. 

3. The component has produced five generic types of improved cooking stoves: 

namely, the charcoal bucket stove, wood stoves with and without chimneys, and 

rice husk stoves with and without chimneys. The absolute heat utilization for 

charcoal and both types of wood stoves increased up to 7% over that of the 

average commercial models. Further, an increase of 5 and 3% was achieved 

with rice husk stoves with and without chimneys respectively. In terms of 

comparative efficiency increases, the charcoal stove reached a 26% increase 

over the average commercial models, while for wood stoves with and without 

chimneys they were 58 and 35% respectively. The increase for the rice husk 

stove with chimney was 100%, or double the efficiency of the average 

commercial models. The rice husk stove without chimney had the least 

increase, 15 - 16%. 

4. The investigation conducted on existing commercial stoves revealed that 

fuel efficient cooking stoves for charcoal, wood, or rice husk are rare. The 

laboratory tests have led to the identification ot the stoves' critical 

physical parameters. They consist of stove weight; exhausted gap/area; 

combustion chamber capacity; rim design for proper fit of variously-sized 

pots and pans; grate-to-pot distance; grate parameters such as hole area, hole 

size and distribution, and thickness; height of chimney, and flue gas baffle 

(for chimneyed stov;es). Other strong factors also influencing stove 

performance are external variables--fuel load or fuel feeding rate, amount of 

water to be boiled, and the wind factor. The information obtained was later 

used for redesigning the improved stove models. 

5. Good quality clay material suitable for stove manufacturing has been 

identified and a production technique has also been developed for small-scale 

and home industries. Local stove manufacturers in one district of Roi-et 

Province were trained without any difficulty in this technique of stove 

production. improved stoves, particularly charcoal and nonchimney wood models, 

are heat refractory and can withstand thermal shock much better than present 

13

commercial ones. In addition, the application of the internal mold has 

greatly improved the precision necessary to control the critical internal 

dimensions. This method was found to be superior'to the traditional one 

using an external mold which hardly conLrolled the internal dimensions. 

6. The production cost of the improved models as described in (2) above 

presently is approximately 2.5 times more than the cost of he poorer quality 

commercial models. Howevdr, when compared with top quality charcoal bucket 

stoves sold in the market, the improved models' cost is 25 - 30% lower. 

Therefore, in long-term commercial production, the improved models will be 

competitive when production increases and more improved stoves reach the 

market. 

7. So far, nine improved stove promotion and training programs have been 

carried out among villagers at various places around the country. The 

reception for the charcoal bucket and the non-chimney wood stoves was very 

gdod, while the good reception of the rice husk chimneyed stove was limited 

to a few localities where only rice husk is available. The chimneyed wood 

and non-chimneyed rice husk stove are of less interest to rural users than the 

charcoal bucket and the non-chimneyed wood and the rice husk chimneyed stove. 

It is believed that with good follow-up and promotional effort, some of the 

improved developed models will withstand harsh use and serve users well in 

rural kitchens. However, these long-term results are yet to be seen. 

8. Because of time constraints, the project had a limited time to approach 

manufacturers on a large scale. However, among a few large manufacturers in 

the Central area, the response to the idea of mass production of the 

developed models was not enthusiastic. This lack of enthusiasm is perhaps 

a result of stove manufacturers being accustomed to the production of their 

rough products and being reluctant to manufacture stoves with which they have 

little or no experience. Moreover, they probably want to see the market for 

high quality, efficient stoves develop first before committing their resources 

to their production. Therefore, more time and more education are needed for 

them to change their attitude and adapt their production techniques. 

14

RECOMMENDATIONS 

On the basis of the overall work of this project, some recommendations 

are presented below: 

1. Because stove development and promotion involve the social customs and 

habits of millions of people in Thailand and around the world, it is highly 

recommended that stove research and development be carried on to furtner 

improve present designs and find more alternatives for users. 

2. Stove development should emphasize each generic type of stove; namely, 

charcoal, wood with and without chimney, and agrirenidue stoves with and 

without chimney so that users have choices. 

3. Stove research and development must not only emphasize the good 

conversion efficiency, but it most also facilitate ease of use and other 

cooking functions, without causing undue change in people's cooking habits. 

4. Stove promotion i.sa most difficult activity. It will take a great 

deal of time and resources. Therefore, continuous effort must be made for 

at least five years with reasonable financial and human resource support in 

order to see a real impact among 6 million rural users. 

5. In Thailand there are quite a few researchers and interest groups working 

on stove development and promotion. Unfortunately, all lack guidelines and 

coordination. For national stove programs to be directed toward this common 

goal, leading government agencies are needed to provide close coordination. 

6. During the course of stove development, many contacts were made with 

experienced stove manufacturers. It was found that, regardless of their 

long experience, their basic understanding of good stove configuration, design 

and its performance was very much lacking. This problem was also manifested 

in the presence of a large majority of poor quality and less efficient 

commercial stoves in the market. Therefore, it is strcngly recommended that 

concerned government agencies take an initiative toward arranging formal 

training programs for the promotion of the essential, scientific knowledge 

required among stove manufacturers. Incentives or approaches such as offering 

a certificate and/or reward to manufacturers of efficient stolres would be 

a highly motivating factor. 

7. The lack of understanding among users on the criteria for selection and 

use of efficiett cooking stoves was also evident. Therefore, the concerned 

government agency should establish a long--range,adequately funded educational 

campaign program for efficient stoves--particularly through primary and 

secondary school systems. 

8. The cost of improved design stove production is still high. If simple 

hydraulic molding can be developed and employed at the village level, 

production costs can be greatly reduced. Under these conditions stove 

dimensions will be more precise and the production rate will be increased 

significantly. 

15

9. Selection of clay raw material and improvement of the clay mixture and 

firing to attain a product with fire resistant characteristics (particularly, 

the charcoal stove body) are essential to a stove's long service life. The 

weight of the stove also needs further reduction (to achieve peak performance 

with even lower charcoal loads). 

10. The improved non-chimneyed wood stove is quite efficient for the present 

developed model. It can conveniently be used to replace three-rock stoves. 

However, the same problems exist in its mass production techniques as ex.st 

for the charcoal stove. 

11. Smoke in the kitchen is a problem inherent in non-chimneyed wood stoves 

including the three-stone and open fire. Research should be carried out in 

Thailand to determine whether smoke from undeveloped and even developed stoves 

(which noticeably gives less smoke over the undeveloped ones), has any 

significant effect on long-term health of users. 

12. Up to the present time, the one hole chimneyed wood stove has attained 

an efficiency up to only 18-19%. In addition, there are problems fitting 

pots and pans to this stove. Therefore, it is recommended that development 

on this type of stove be continued in order to improve both heat utilization 

efficiency and compatability with various pots and pans. Moreover, the stove 

material (as in the case of the non-chimneyed wood stoves and the charcoal 

stove) shoul] also be investigated. 

13. Even though, at present, the chimneyed rice husk stove is still not 

popularly used in Thailand, the chance for this stove to become popular in 

certain regions is high. This is because it can use granulated fuels other 

than rice husk (such as sawdust, peanut shell, seed waste, household biomass 

scraps, etc). There are several further improvements that need consideration. 

These include the improvement of the stove's configuration to fit various 

pots and pans and reduction of its weight so that sometimes it can be moved 

around the house (yard) when needed. For two people to carry the stove, the 

weight should not exceed 50 kg. 

14. The experience gained from the stove promotional campaigns among rural 

users, even in its short duration, strongly indicated that there is a good 

chance of success in replacing relatively inefficient stoves among 6 million 

rural Thai families with efficient stoves. It is, therefore, recommended that 

the government support a nationwide efficient stove promotional campaign for 

users and manufacturers as soon as possible. 

15. Since better biomass cooking stoves, in part, mean better living 

for millions of rural families around the world, the idea of 

continuous development to attain even better performance than the present 

developed models should be the challenging subject among applied research 

scientists and concerned institutions. 

16

LIST OF TABLES 

Table Title Page 

4.1 -.Characteristics of Biomass fuel use in the experiment ooo........ 64 

5.1 Physical dimensions of tested charcoal stoves .......... ... 80 

5.2 Physical dimensions of tested wood stoves without chimneys ...... 82 

5.3 Physical dimensions of tested wood stoves with chimneys ......... 84 

5.4 Physical dimensions of rice husk stoves without chimney ......... 86 

5.5 Physical dimensions of rice husk stoves with chimney ............ 87 

5.6 Average testing results of commercial charcoal stoves ........... 88 

5.7 Average testing results of wood stoves without chimney .......... 96 

5.8 Average testing results of wood stoves with chimney ............. 97 

5.9 Average testing results of rice husk stoves with chimney .........98 

5.10 Average testing results of rice husk stoves without chimney ..... 100 

5.11 Test result of the effect of stove gap/exhausted area 

on HU and time to bo>i ........................................... 103 

5.12 Test results of the effect of grate hole area on HU and 

time to boil .............................................. 104 

5.13 Test re;ult of the effect of grate-to-pot distance on HU 

and time to boil ............................................... 107 

5.14 Test result of the effect of combustion chamber size on 

HU and time to boil ............................................. 108 

5.15 Test result of the effect of air inlet door on HU and 

time to boil ....................................................110 

5.16 Test result of the effect of grate thickness on stove 

performance ..................................................... 113 

5.17 Test result of the effect of insulation on HU and time to boil ...113 

5.18 Test result of the effect of stove weight on the HU 

and time to boil ................................................ 115 

5.19 Test result of the effect of initial weight of charcoal 

on stove HU and time to boil ................................... 116 

17

LIST OF TABLES (continued) 


5.20 Test result of the effect of initial weight of water 

on HU and time to boil .......................................... 

5.21 Test result of the effect of pot size on HU and time to boil .... 119 

5.22 Test result of the effect of charcoal size on HU and time 

to boil ......................................................... 120 

5.23 Test result of the effect of wind on HU and time to boil ........ 121 

5.24 Test result of the effect of air relative humidity on 

HU and time to boil ............................................. 122 

5.25 Test result of the effect of stove gap on HU and time 

to boil of the wood stove ....................................... 123 

5.26 Test result of the effect of grate on HU and time to 

boil of wood stove .............................................. 124 

5.27 Test result of the effect of grate hole area on wood 

stove performance ............................................... 126 

5.28 Test result of the effect of grate-to-pot distance on 


5.29 Test result of the effect of wind on wood stove performance ..... 128 

5.30 Test result of the effect of firewood feeding rate on the 


6.1 Group of stoves that have similar behavior and show good 

correlation in regression analysis .............................. 150 

7.1 Physical characteristics of RFD-1 charcoal stove relating 

to external variablec ........................................... 174 

7.2 Average test results of RFD-I charcoal stove under 

different use conditions ........................................ 174 

7.3 Test results of improved nonchimneyed wood stove model 

RFD-2 with bucket ............................................... 179 

7.4 Performance of the prototype improved chimneyed wood stove ...... 185 

7.5 Test results of improved chimneyed rice husk stove model RFD-3 .. 191 

8.1 Compositions and fired resistant property of some local 

clay materials used for stove and pottery productions ........... 199 

18 

117

LIST OF TABLES (continued) 


941 Comparison test for efficiency.between developed and 

commercial stoves in Mahasarakarm ............................... 217 

9.2 Comparison test for efficiency between developed and 

commercial stoves in Saraburi ................................... 219 


commercial stoves in Sakolnakorn ................................ 221 


commercial stoves in Pitsanulok ................................. 225 




commercial stoves in Chachoengsoa ............................... 227 


commercial stoves in Mahasarakarm ............................... 228 




commercial stoves in Nan ........................................ 231 

19

LIST OF FIGURES 

Figure Title Page 

5.0 Time-temperature characteristic curves of charcoal 

bucket stoves ......................................... ..... ... 90 

5.1 Pe,-t rmance rating based on heat utilization efficiency 

(HU) of commercial charcoal bucket stoves ........................ 91 

5.2 Performance rating based on time to boil of commercial 

charcoal bucket stoves .......................................... 92 

5.3 Performance rating based on heat utilization efficiency 

(HU) of nonchimneyed and chimneyed wood stoves .................. 94 

5.4 Performance rating based on time to boil of nonchimneyed 

and chimneyed wood stoves ....................................... 95 

5.5 Performance rating based on heat utilization efficiency 

(HU) of nonchimneyed and chimneyed rice husk stoves ............. 101 

5.6 Performance rating based on time to boll of nonchimneyed 

and chimneyed rice husk stoves .................................. 102 

5.7 The effect of exhausted gap on the stove efficiency and 

time to boil ...................................................105 

5.8 The effect of the grate hole area on the stove efficiency 

and time to boil ...... ............ ............................. 106 

5.9 The effect of grate--to-pot distance on the stove 

efficiency and time to boil .................................... 109 

5.10 The effect of combustion chamber volume on the stove 

efficiency and time to boil of three different stoves tested .... 11 

5.11 The effect of air inlet door on the stove efficiency 


5.12 The effect of grate thickness on the stove efficiency 

and time to boil ...................... 

5.13 The effect of the initial weight of charcoal on the 

stove efficiency and time to boil ............................... 118 

5.14 The effect of exhausted gap on efficiency of various 

wood stoves ................................................... 

5.15 The effect of grate-to-pot distance on the heat utilization 

efficiency (HU) of wood stoves .................................. 129 

6.1 Structure of the ideal Biomass cooking stove ................. 137 

P-,. 21 

114 

125

LIST OF FIGURES (continued) 


6.2 Geometry of the ideal stove ..................................... 145 

6.3 Relationship between the area of the opening for inlet 

air and the grate hole area ..................................... 147 

6.4 Relationship between exhaust area and gap height ................ 148 

6.5 Relationship between variable X, defined in equation (49), 


6.6 Model prediction of the effect of grate-to-pot distance 

on the stove efficiency, stove mass and time to boil ............ 153 

6.7 Model prediction of the effect of wall thickness on the 

stove efficiency, stove mass and time to boil ................... 154 

6.8 Model prediction of the effect of inside diameter of stove 

at the bottom on the stove efficiency, stove mass and time 

to boil ......................................................... 156 

6.9 Model prediction of the effect of inside diameter of stove 

at the pot stand on the stove efficiency, stove mass and 

time to boil ................................................... 157 

6.10 Model prediction of the effect of gap height on the stove 

efficiency, stove mass and time to boil ......................... 158 

6.11 Model prediction of the effect of grate diameter on the 


6.12 Model prediction of the effect of grate hole area on the 


7.1 Drawing of improved charcoal bucket stove showing various 

parts of the construction and terminology ....................... 168 

7.2 Drawing of improved nonchimneyed wood stove showing parts 

of the construction and terminology ............................. 169 

7.3 Drawing of developed chimneyed wood stove prototype 

showing the construction and terminology ........................ 170 

7.4 Drawing of improved nonchimneyed rice husk stove showing 

the construction and terminology ......................... ...... 171 

7.5 Drawing of improved chimneyed rice husk stove showing the 

construction and terminology ............................ .. . 172 

7.6 Improved charcoal stove model "RFD-I" ...... ...... .177 

22

LIST OF FIGURES (continued) 


7.7 Improved charcoal stove model "RFD-I" .......................... 178 

7.8 Improved nonchimneyed wood stove model "RFD-2"................... 181 

7.9 Improved nonchimneyed wood stove model "RFD-2" ................. 182 

7.10 Prototype of developed chimneyed wood stove showing 

different parts of construction ................................ 183 

7.11 Nonchimneyed rice husk stove, the "Improved Meechai" model ..... 189 

7.12 Improved rice husk stove with chimney, the "RFD-3" model ....... 193 

8.1 Technical Drawing of the Improved Charcoal Stove ............... 201 

8.2 Technical Drawing of the Improved Wood Stove ................... 202 

8.3 Technical Drawing of the Improved Rice Husk Nonchimneyed Stove . 203 

8.4 Technical Drawing of the Improved Rice Husk Stove with 

Chimney ........................................................ 204 

8.5 Preparation of biscuits and firing to be used later for 

clay mixture ................................................... 205 

8.6 Production of charcoal stove on the potter's wheel 

using the internal mold ........................................ 205 

8.7 Disassembling of the internal mold from a newly made 

charcoal stove ................................................. 206 

8.8 Improved charcoal and wood stove after finished firing 

and ready for further fabrication .............................. 206 

8.9 Grate hole design for charcoal stoves .......................... 208 

8.10 100-ton hydraulic automatic press machine for charcoal 

and wood stove ................................................. 210 

9.1 Introduction of developed stoves to participants ............... 233 

9.2 Stove contest for efficiency comparison between commercial 

stoves and developed models .................................... 233 

9.3 Trainee participation in installing stov's parts .............. 234 

9.4 Distribution of developed stoves to all participants ........... 234 

23

A total surface area, sq cm 

A e 

A g 

A i 

c pw 

gap area, sq cm 

TERMS AND ABBREVIATIONS 

grate hole area, sq cm 

area of opening for the inlet air, sq cm 

heat capacity of wLter, J/gm C 

D wall thickness, cm 

D b 

D g 

Dt db outside diameter of the stove at the bottom, cm 

outside diameter of the stove at the grate position, cm 

outside diameter of the stove at the pot stand, cm 

inside diameter of the stove at the bottom, Cm 

d inside diameter of the stove at the grate position, cm 

g 

d t 

E c 

inside diameter of the stove at the pot stand, cm 

heating value of charcoal, 26340 J/gm 

Ef heating value of fuel, J/gm 

Ek heating value of wood kindling, 17890 J/gm 

F12 view factor from surface 1 to surface 2 

G gap height, cm 

Gr Grashof number 

AH heat of combustion, J/gm 

H grate-to-pot distance, cm 

Hba distance between the base and the apex of the outside cone, cm 

Hg b 

distance between the grate and the base of the outside truvcated 

cone, cm 

25

Htg distance between the grate and the potstand of the outside cone, 

cm 

HU heat utilization efficiency, % 

h heat transfer coefficient, W/sw cm C 

hba distance between the base and the apex of the inside cone, cm 

hfg latent heat of vaporization, J/gm 

hg b 

distance between the grate and the base of the inside truncated 

cone, cm 

htg distance between the grate and the pot stand of the inside cone, 

cm 

k thermal conductivity, J/cm s'C 

L heat of vaporization of water at lO0C, 2256 J/gm 

mc mass oZ charcoal, gm 

m stove weight, kg 

I rate of evaporatcd water, gm/s 

V 

m initial weight of water, gm 

Qabs rate of heat absorption, J/s 

Qh rate of heat supplied to water, J/s 

QI rate of heat loss, J/s 

Qsens sensible heat of water, J 

&w rate of heat absorbed by water, J/s 

qcond heat flux by conduction, J/s sq cm 

c dd heat flux by radiation, J/s sq cm 

S specific heat of water, 4.18 J/gm 

surface area of pot, sq cm 

T temperature, 0 C 

Tamb ambient room temperature, 0 C 

Tboil boiling water temperature, 'C 

T water temperature, 'C 

26

T temperature of water at start of test, OC 

T 2 

temperature of water at boiliDg point, *C 

TTB time to boil, min 

t time, min 

vc velocity of buoyant gas, cm/s 

W weight of water in pot at start of test, gm 

W c 

W e 

weight of charcoal remaining at end of each test, gm 

weight of water evaporated at end of each test, gm 

Wf weight of fuel used, gm 

Wk weight of kindling, gm 

p density, g/cu cm 

a Stefan-Boltzmann consta.t 

efficiency of stove, % 

27

Chapter 1 

Introduction

INTRODUCTION 

This publication presents th3 major findings on the testing and 

development of biomass cooking stoves in Thailand--stoves that use wood, 

chtrcoal and agricultural residues. The Stove Improvement Project has four 

major parts responsible for different project functions; 

1. Stove Testing: Selection of available commercial stoves to be tested; 

2. Stove Development: Measurement and analysis of stove performance to 

yield designs of new models; 

3. Stove Construction and Fabrication: Production of engineering drawings 

of the newly developed designs as well as construction and fabrication 

of the stoves; and 

4. Stove Promotion: Carrying out field promotion for the newly developed, 

highly efficient stoves. 

A. THE PROJECT 

Stove Improvement is one component of 14 separate components involved in 

the Renewable Nonconventional Energy Project #493-0304. Projects carried out 

include: 

Industrial Biogas 

Biomass Gasification 

Charcoal Improvement 

Energy Master Plan Support 

Micro-Hydro Project 

National Energy Information Center 

Pyrolysis of Rice Husks 

Regional Energy Centers 

Solar Thermal Processes 

Solar/Wind Assessment 

Stove Improvement 

Village Survey 

Village Woodlots 

Water Lifting Technology 

This Project is jointly funded by the United States Agency for 

International Development (USAID) and the Royal Thai Government through the 

National Energy Administration (NEA) and Royal Forest Department. The Stove 

Improvement program is operated by the Forest Products Research Division of 

the Royal Forest Department. 

31

B. HISTORICAL BACKGROUND 

This section briefly discusses the evolution of cooking stoves in the 

world (and Thai cocking stoves in particular) in terms of popular types of 

hardware and cultural and social habits associated with various models. 

Evolution of Cooking Stoves in the World 

Evidence of the use of biomass fuel, particularly wood, has been found 

within the caves of Peking man as early as 400,000 years ago (Bronowski,1973). 

At that time, biomass was presumably used as fuel for weather conditioning 

(warmth). Its application to cooking developed later. While styles and 

methods of cooking have developed into a variety of artistic and elaborate 

forms, the biomass cooking stoves which are the hardwar-e supporting this 

activity (as holders for cooking utensils and as fuel combustion chambers) 

have changed very littlu in structure and performance from their ancient 

predecessors. 

When compared with modern stoves such as oil, gas, and electric, the 

biomass cooking stoves are far less efficient. The efficiency of kerosene or 

LPG fuelled stoves can be as high as 45-48%, while that of a wood stove 

averages only 15-20%. Even though the -ap in efficiency is partially explained 

by the lower calorific value of the wood fuel, the main problem still rests 

heavily on the hardware design of the stove itself. 

The development of stoves can be seen as eccurring over two periods of 

time. The first period began with the birth of the three stone stove and 

continued until the discovery and application of electricity. The second 

period has lasted from that time until the present. While the latter period 

amounts to only about 100 years, the first period lasted many thousands of 

years. 

The slow development of biomass cooking stoves in the early period can 

be explained by the abundant supply of wood and the consequent lack of any 

demand for higher efficiency stoves. Most of the effort toward improved stove 

design in the second period of time has been in the area of the electric, gas, 

and oil stoves popular in western countries. The application of scientific 

principles and knowledge to the design of better biomass cooking stoves has 

been neglected. However, as the world population has increased tremendously 

in the last 100 years, particularly in poor and less developed countries Lhat 

are dependent on biomass cooking stoves, the demand for wood fuel has risen 

sharply. The increase in demand coupled with the rapid loss of forest land 

to agriculture has made the procurement of wood for cooking both difficult 

and expensive. With the current situation, the time has come for humankind 

to start applying modern engineering principles to the design of biomass 

cooking stoves in order to improve this long neglected but widely and daily 

used appliance. 

32

History of Thai Cooking Stoves 

In Thailand, as in many developing countries, a large majority of people 

cook meals with biomass fuels. The largest proportio.. of biomass fuel 

consumption consists mainly of wood (59.8%) and charcoal (29.9%) (Pounoum, 

Wongopalert, and Arnold 1982). Other types of biomass used as cooking fuel 

make a considerably smaller contribution. These include rice husk (8.0%), 

rice straw (1.7%), and coconut shell (0.6%). The wood and charcoal consumption 

in terms of solid wood are reported to be 40 million cubic meters annually. 

The quantity of solid fuel used for cooking is certainly going to increase in 

the near future because of the increase in population. Substitution with other 

fuels will be limited. This increasing trend of fuelwood consumption cannot 

be ignored because it results in a greater demand on the fuelwood supply. In 

fact, a fuelwood scarcity has already occurred in many areas of the country. 

Cooking in Thailand relies heavily on wood because of its ideal nature 

as a fuel. However, most of the biomass stoves used by Thai families are still 

inefficient. If the efficiency of the stove could be improved by only 5-10% 

(in fact 50% improvement can be achieved over the average commercial models), 

the quantity of wood and charcoal consumed by 6 million rural families in 

Thailand can be greatly reduced. 

A survey of popular types of biomass cooking stoves is very essential 

because it can be used as a guideline for stove improving strategies. Many 

new designs of highly efficient stoves have failed to gain popular acceptance 

because the new models require changes in family cooking habits and social 

traditions. In addition, the operation of newly introduced designs is often 

more difficult. Hence, some important factors influencing the acceptance of 

highly efficient stoves by rural families are considered in the following 

discussion of hardware and cultural and social habits. 

PopuZar types of hardware 

A survey of cooking hardware used by Thai rural families (Pounoum, 

Wongopalert, and Arnold 1982) reported that the most popular type was a 

bucket stove which accounted for 71% of rural families. Eighteen percent of 

rural families use the three-stone stove and 11% use other types of stoves 

that use fuel such as rice husk, sawdust, biogas, etc. The bucket stoves 

commercially sold in the markets are primarily designed for charcoal. However, 

some bucket stoves are designed for dual purposes where either charcoal or 

wood can be used for fuel. Unfortunately, these dual features have 

significantly compromised the stove efficiency (to be discussed later in this 

report). Prices vary from 20 baht to 300 baht depending on design, workmanship 

and bucket materials. For example, a stainless steel bucket stove may 

cost 150 baht a piece: it is the most expensive stove. 

The bucket stove is believed to have originated in China as it is known 

by Chinese name, "Ang-lo", which means "red color" (the color of low 

temperature fired clay). The period in which the bucket stove was brought 

to Thailand is not known. It possibly could have been brought here as long 

as 1,000 years ago during the earliest trade between Thailand and China during 

the Sukhothai Period. Or, on the other hand, the bucket stove may have come 

33

with Chinese migration during the Chinese civil war because the word "Ang- 

Lo" is from the dialect of one Chinese ethnic group that migrated to Thailand 

in large numbers during that time. If this is true, then the time of its 

appearance in Thailand would be only about 100 years ago. 

The three-stone is really an ancient cooking stove used throughout the 

world that may have originated hundreds of thousands of years ago. It still 

exists today, and in Thailand is used only with wood. For other oiomass, 

such as rice husk, sawdust, and peanut shells, the other stove is used, 

particularly in central areas where fuelwood is scarce. Rice husk stoves 

normally include chimneys because burning husks requires an induced draught 

to facilitate continuous combustion. Recently, non-chimney rice husk stoves 

have been found being used by some Kampuchean refugee families at Kao-I-Dang, 

Refugee Camp in eastern Thailand. Both types of rice husk stoves, chimney and 

non-chimney, have not been widely used in Thailand so far. 

Cutlturci and .ociaZ habits 

The size of a Thai family averages 6 persons. To cook food for this 

number of people usually takes about 45 minutes to 1 hour. Most of the 

cooking is of rice (boiling or steaming), with an average cooking time of 

about 15-30 minutes. Meat and vegetable dishes are usually cooked rapidly 

thereafter and, hence, the cooking time is less than 10 minutes/dish. This 

kind of cooking always requires high heat intensity, and therefore, a onehole 

stove is preferred over multiple ones. Furthermore, in Thai culture, 

members of the family do not gather around the fireplace after the meal, 

drinking tea or coffee. Hence, the second pot hole (used for warming a hot 

drink) is not needed. Neither hot water for bathing nor room heating is 

required. 

For these characteristics and cooking practices of Thai families, the 

bucket stove is considered the most suitable and, therefore, has become the 

most popular type of cooking stove throughout the country. It is believed 

that at least 4 million bucket stoves are being employed in Thailand at 

present. 

C. STATEMENT OF THE PROBLEM 

The problems associated with biomass cooking stoves are discussed in the 

following section. 

Use of Inefficient Cooking Stoves 

Rough efficiency tests have been performed on commercial charcoal, wood 

as well as three-stone stoves at the user end (Pounoum, Wongopalert, and 

Arnold 1982). It was found that most biomass stoves are inefficient. For 

example, the average efficiency of wood burning stoves is 13.6%, and charcoal 

bucket stoves 21.6%. The low efficiency performance of cooking stoves is due 

mainly to poor design. For instance, the bucket stoves available on the 

market usually have an overly large exhaust gap through which a large 

34

quantity of sensible heat escapes. The stove rim is also poorly designed 

and can accommodate only a few pots and pans. Some wood stoves do not have 

grates and hence air for combustion is distributed pQorly, resulting in 

poor combustion of the fuel. 

Lack of Knowledge and Awareness in Selecting Good Stoves 

Almost all people who use biomass cooking stoves daily seem to be 

unconcerned about the stove performance. This may be due to the lack of 

awareness and knowledge of how a good stove could perform and the inability 

to recognize higher efficiency stoves. The selection of the appropriate type 

of stove for specific biomass fuel is also very important. For example, if 

charcoal is uced in a bucket stove designed for wood, the efficiency of that 

stove will be reduced at least oy 5-10%. 

Lack of Interest and Knowledge axnong Manufacturers in the 

Production of Good Stoves 

Even though there exist some large bucket stove manufacturers in Thailand. 

the majority of biomass cooking stoves are generally produced within family 

industries where members of the family do the work. Stove manufacturing 

knowledge (or poor knowledge) and skill has usually been passed down through 

new members over time. However, after conversing with many manufacturers, it 

was found that most of them still lack the interest and knowledge to recogPize 

the essential features of good stoves. The idea of competing for cheaper 

products among stove manufacturers without concern for quality is quite 

prominent. This has brought about poor efficiency and durability of stoves 

on the market. 

Lack of Knowledge of Stove Maintenance 

Commercial stoves are made of a low temperature fired clay material. 

Their durability when exposed to very high temperatures, such as the hot 

glowing charcoal bed in the combustion chamber, is such that it will last 

only about 3-6 months at the most without an outside restraining device. If 

this fired clay stove is bucketted and prorerly filled with insulating 

materials and lined around the inside wall with an inexpensive refractory 

mixture, the service life of the stove can be prolonged to approximately 1 

year. Good care of stoves such as the repairing or the replacing of the 

grate, refractory lining, and rim sealing can greatly help to extend the 

stoves life expectancy. Unfortunately, most household tenders also lack 

this knowledge. In addition, it has been found that quite often the stove 

is overloaded with charcoal above the combustion chamber and hence, the 

cooking pot that rests on the charcoal bed will directly assert its own 

weight on to the grate. This will daanage the grate and cause stove 

degradation. Hot liquid splashing on to the stove rim and inside the 

combustion chamber due to severe boiling also affects the stove's life 

expectancy because it will cause the stove's rim and body to crack. 

35

Lack of Understanding of Fuel Preparation 

Wet fuel burns less effectively than dry fuel because part of the heat 

of combustion is consumed to evaporate the water. Fresh wood generally 

contains about 50% moisture; therefore, wood should be ideally dried down to 

a moistura content of approximately 15%-12% before use. This can be done 

easily by placing it under the grate during cooking, or by letting it air dry 

for several days after splitting. It was found that many househola cooks do 

not practice fuelwood preparation and drying. Another factor that 

contributes to the inefficient consumption of fuel is the lack of understanding 

of fuel use. For example, some household cooks insert a large piece of log 

into the stove. This kind of practice not only prolongs cooking time but also 

requires more firewood. In addition, the heavy wood piece can damage the 

stove structure easily. Smaller sized wood burns more effectively than fuel 

of a larger size, since a smaller size has a larger surface area of combustion 

with air. Therefore, large pieces of wood should be split or chopped into 

smaller ones for more efficient use of fuel. 

High Cost, Limited Production and Distribution of Good Stoves 

Since the main energy sources for cooking in Thailand are wood and 

charcoal, the degradation of natural forest has become evident in many areas 

of the country. The rate of deforestation has increased tremendously during 

the last decade. For example, the forest areas of the country have been 

reduced from 273,628 sq.km. in 1961 to 156,600 sq.km. in 1982 (Forestry 

Statistics 1982). Even though the depletion of the forest is not only caused 

by the consumption of fuelwood for cooking but also by slash and burn 

agriculture, road construction, etc., 40 million cu.m./yr of wood fuel is 

used for cooking alone. This will contribute significantly to the wood 

scarcity problem in the near future. 

Fortunately, commercial, fast-growing tree plantations that produce fuel 

(such as the mangrove, Eucalyptus, and Casuarina) can somewhat reduce the 

depletion of wood. However, if the commercial wood plantations are not 

expanded on a large scale, or are developed without the attempt to reduce 

heavy woodfuel consumption by initiation of efficient stoves, or by encouraging 

the people to grow more wood for their own use, Thailand's natural forests 

can become exhaused within a very short time. 

D. OBJECTIVES OF THE STUDY 

The following are the five major objectives of the study: 

1. Tu established a model stove testing and evaluation center to 

accommodate the national need for present and future research and 

development of biomass cooking stoves. 

2. To conduct a systematic investigation on present performance of existing 

stoves being used in Thailand. 

36

3. To make necessary improvements in terms of heat conversion efficiency, 

ease of operation and durability for three generic types of stove; 

namely, charcoal, wood, and rice husk/agriresidue. 

4. To develop an improved stove production technique suitable for present 

small scale and medium scale rural industries. 

5. To disseminate information, improved hardware and/or technology generated 

by this study to stove users, manufacturers, and the general public. 

E. POTENTIAL BENEFITS FOR RURAL DEVELOPMENT 

The potential benefits expected to be gained by the people who live in 

rural areas of Thailand are: 

1. Decrease in national overall fuelwood consumption, and hence, an indirect 

decrease in the rate of deforestation. 

2. Helping stimulate the establishment of indigenous renewable sources of 

energy in community, village and private woodlots through the popular 

employment of efficient biomass cooking stoves. 

3. Retarding the rate of increase of imported petroleum derived cooking 

fuels. 

4. Reduction of cooking time as well as ease of cooking through the use of 

highly efficient stoves and also a plausible reduction in kitchen air 

pollutants due to mre complete combustion of the fuel. 

5. Individual savings on stove costs and woodfuel costs due 

life and better efficiency. 

to longer service 

6. The improvement of material and technology for constructing the developed 

stoves combined with the better understanding of stove operation, care, 

and maintenance will altogether help the economy of stove producers and 

users in the long run. 

F. SCOPE OF WORK 

The stove improvement component project was designed to invertigate types 

of biomass fuels and types of cooking stoves. Charcoal, wood, and rice husk 

are the prominent biomass fuels used in Thailand and, hence, were to be 

selected for this study. The popular types of cooking stoves among users and 

those which are strictly used for household cooking were to be chosen for stove 

development. A detailed scope of work which includes laboratory set up, stove 

testing, analyses of stove performance, designs of developed models, 

construction and fabrication, and stove promotion follows. These lists 

present the steps that were to be taken for all aspects of the project. 

37

Laboratory Set Up 

1. Selection of the site and laboratory construction at the Royal Forest 

Department. 

2. Acquisition of test instruments and facilities. 

3. Acquisition of technical consultants and researchers. 

Stove Testing Program 

1. Collect from the field various models of stoves used in different parts 

of Thailand. 

2. Select fuels to be used in tests and determine standard fuel preparatior 

methods. 

3. Select appropriate cooking and water boiling experiments and techniques. 

4. Test the cooking stoves according to the selected testing experiment. 

Analyses of Stove Performance Yield Design of Improved Model 

1. For each model tested, determine the design parameters to be modified. 

2. Measure the performance of stove models and the effects of changas in 

design parameters; performance measures include fuel consumption, rate 

of heat generation, cooking and boiling times, and efficiency 

determination. 

3. Select stove designs which have good performance characteristics. 

4. Design the prototype of developed models. 

Stove Construction and Fabrication 

1. Discuss with village craftsmen the methods of fabrication, the materials 

available for fabrication and the cost of constructing the units. 

.2. Select and improve clay materials for stove production. 

3. Improve technique of stove production. 

4. Trial production of developed stoves in actual small scale rural stove 

manufacturing factories. 

5. Prepare stove guideline for fabrication, use, and maintenance. 

6. Prepare technical drawings of developed stoves. 

38

Stove Promotion 

1. Introduce developed stoves through gwernment agencies and villagers 

via training courses, and informatioh!brochure distribution. 

2. Organize stove manufacturers to produce improved design stoves. 

3. Distribute stove sampleb to household users in rural areas via Regional 

Energy Center of NEA. 

39

Chapter 2 

Review of Literature 

Par. ., 'Z , ,, " " j. 

" ' ' 2- c.

REVIEW OF LITERATURE 

Biomass cooking stoves have been used by human beings for a long time 

but the knowledge of how various stove designs perform under different 

conditions is still vague. Most of the work done in the past was directed 

at trying to improve stove configuration; a few studies attempted to 

develop methods of testing stove performance. In this Chapter, a review of 

stove construction and design, methods of testing stove performance, and 

factors affecting stove performance will be presented. 

A. STOVE CONSTRUCTION AND DESIGN 

Various stove configurations are seen in Thailand and overseas. The 

variation comes about as a consequence of cooking habits and simplicity. 

In some countries people prefer to sit while cooking, while in others 

standing is preferred. To suit such cooking habits, stoves are constructed 

differently. In this section, construction and design of open fire Thai 

stoves, and overseas stoves are reviewed. 

Open Fire Stoves 

The open fire stove is a primitive stove which is still widely used in 

the developing world. The fire is encircled by more stones, bricks,cement, 

or lumps of other incombustible material. The open fire stovesometimes 

called the three-stone stove (or fire), has no cost; no special materials 

or tools are needed to construct it and it can be located anywhere. 

Moreover, the heat output from the fire can be controlled by adding or 

withdrawing fuel. 

Many different arrangements are found. Many countries use metal trivets; 

the trivet consists of a horizontal metal ring to which three legs are 

attached. in Senagal, 55% of the rural population uses trivets (Modon et 

al., 1982). 

Thai Stoves 

A variety of stoves can be found in Thailand, both user built and 

commercially manufactured. Charcoal bucket stoves, which can be found almost 

everywhere in Thailand, have been studied by Thai investigators (Osuwan and 

Boonyakiat, 1982). The structure of this stove will be described in a later 

chapter, The book by Dunn, et al.(1982) and De Lepeleria.et al.(1981) also 

has detailed descriptions. Since the Thai charcoal bucket stove was 

investigated in this study, it is appropriate to review the literature and 

the various investigations already conducted. 

43

Thai Charcoal Bucket Stove 

Although there are various kinds of bucket stoves in Thailand, they 

have a common structure. The stove is normally made of fired clay in the 

shape of an inverse truncated cone, (or cylinder) which is placed in a 

metal (generally zinc) bucket-liked container; hence, the name "bucket 

stove." Charcoal is the main fuel for this kind of stove. 

In 1982, Meta Systems Inc. Thai Group, sponsored by USAID, investigated 

the performance of Thai charcoal bucket stoves made by different local 

manufacturers (Pounoumet al., 1982). The group utilized boiling water tests 

and cooking tests (described later in this chapter) in their study. Using 

the water boiling tests, they found that the ratio between the water and the 

fuel affected stove performance more than the size of stove and cooking 

vessel. Time to boil ranged from 11 to 51 minutes. Pounoum et al.(1982) 

also considered the effect of starter fuels on stove efficiency, since 

starter fuels vary among villagers. Using the "cooking test," they compared 

the quantities of fuel, food and water used in cooking rice. The average 

amount of released heat from the fuel consumed was found to be 3.2 kilocalories 

per gram of food cooked. Further, stove efficiency obtained from 

"the water boiling test" demonstrated that the average value used by food 

in cooking was 650 calories per gram of food. 

Osuwan and Boonyakiat (1982) applied water boiling tests to examine the 

performance of Thai charcoal bucket lLoves. They found that stove performance 

was affected by stove size, air inlet area, gap height, grate hole area, 

aluminium pot size, quantity of water used in the test, and quantity and mass 

of charcoal. Their results showed that stove performance improves if stove 

diameter is increased, or the air inlet area is decreased, or the gap height 

is reduced. The efficiency of stove performance varied from 20.86 to 33.95%. 

feechai rice husk stove (Meechai, undated) 

The Meechai stove *iscomposed of four structural metal pieces: a cone, 

a stove body, stands, and an ash receiver. The cone, the stove body and 

the ash receiver are made from scrap metal or galvanized sheet; the stands 

are steel rods. The stove body is put into the cone, which itself is set 

on the stands; rice husks fill the space between the stove body and the cone. 

At the apex of the cone, an ash removal service is positioned to let the ash 

fall out of the stove. 

Sooksunt economy stove (Sooksunt, 198Z) 

The Sooksunt stove can be made of bricks, cement, or a mixture of clay 

and rice husk. It has a chimney. There are three types. Type 1 can be 

used with any kind of fuel except rice husk and sawdust. Type 2 can be 

used with any fuel. Type 3 is designed for the Hill Tribes in Thailand and 

cannot use rice husk or sawdust as fuel. Detailed designs can be found in 

the article by Sooksunt (1981). 

The rice cooking test was performed to test cooking time. For a 

family of 5 people, the Sooksunt stove can steam rice in 30 minutes. The 

time used as reported was not much different from that required by gas stoves. 

44

The stove is recommended for a medium income family (Intrapanich, 1981) 

because it can use any waste materials as fuels. 

Swat stove (Suwat, undated) 

The Suwat 6tove has two pot holes; each pot hole is made from steel and 

insulated with sand, ash, clay, and cement. The first pot hole is above the 

combustion chamber; the second is located between the first and a steel 

chimney. An efficiency of approximately 23% has been obtained from the stove 

when sawdust is used as fuel, ana 17% when rubber wood wastes are used. 

Nai La stove 

The Nai La stove is made from a cylindrical paint can, 6-7 inches in 

diameter and 12 inches high. At the lower part of the can, 2" x 2" air 

inlet hole is cut away to be used as the ignition port. Since the stove is 

made from a can, it is sometimes called a "canned stove" (Bumroong, 1981). 

Fuels used are normally sawdust and rice husk, The packing of fuel is 

achieved by placing a long bamboo stick or a pipe at the axis of the can. 

After the can is filled with fuel and compressed in the bucket, the stick 

is pulled out, leaving a hole for combustion along the tunnel from the 

outway ignition port. 

It has been found that stove efficiencies are 14-16%, and 12% when 

sawdust and rice husk are used as fuel, respectively. 

Noi Palipu (1981) has improved this stove in both construction materials 

and size to gain more durability and reliability for daily practical use. 

This stove has been recommended for the family with low income since 

the material for construction is inexpensive and easy to find (Intrapanich, 

1981). 

Economy fixed stove 

The Economy fixed stove is made of cement and brick, or clay. There 

are two pot seats aligned with a chimney. The stove base is tilted such 

that the distance between the base and the chimney is lower than that between 

the base and the pot seat. Fuel can be wood or rice husk. 

Overseas Stoves 

Stoves found in developing countries are summarized below. 

Traditional stoves 

The traditional Bangladesh Chula consists of a short, slightly downwardsloping 

tunnel dug into the ground, with a pothol, cut in the roof at the 

end. The fire is lit beneath the pot and is kept alight by feeding it with 

fuel pushed in from the open end of the tunnel. In some cases, the size of 

the firing chamber is increased, and two potholes are provided. The depth 

45

of the firing chamber in these Chula stoves is approximately 40-55 cm. (Omar, 

undated). 

Tungku Muntilan (Joseph et aL, 1980) report that a traditional stove 

constructed in Magelang, Central Java, Indonesia, is constructed from clay 

and has approximate dimensions of 65 cm x 33 cm x 22 cm. It weighs 

approximately 20 kgs. There are two poL seats, the second acting as a chimney. 

The stove is sun dried, not fired. It hardens after use in the kitchen. 

Portable stoves 

In Kenya and other East African countries, a metal stove called a Jiko 

(Foley and Moss, 1983) is made from scrap metals in the form of a cylinder 

approximately 25 cm in diameter and 15 cm high. It has a perforated metal 

grage mid-height. Pot supports are fixed to the top edge and project 

inward a few centimeters. Fueling is done by feeding small pieces of 

charcoal around and under the pot, or by lifting the pot. Ashes are removed 

through a small side door at the base of the stove. This door can be used 

as a means of controlling the flow of air to the grate. 

In India, a stove made of light sheet steel is equipped with a carrying 

handle, like that on the bucket. In some areas, the stove is lined with 

mud and cement. This insulates the stove, and cuts down on the radiant heat 

loss from tne sides (Gupta and Usha, 1980). 

A cylindrical stove with an outside wall of steel and an inner lining 

of cement is also used in Indonesia. The grate consists of iron bars fixed 

into the lining (de Lepeleire et aL, 1981). 

The Rural Znergy Laboratory of the Central Power Research Institute, 

Bangalore (India), has developed a stove, called a Priyagni (Cookstove 

Bulletin, 1984). The stove is cylindrically shaped with metal stands to 

keep it steady and help in moving it. A cylindral combustion chamber closed 

both at the top and the bottom has slotted plates of a particular pattern, 

A grate is fitted inside the chamber slightly above the bottom slotted plate. 

The dimensions of the slotted plate and the chamber have been proportioned 

to achieve improved combustion. An aluminium sheet lining is also provided 

in the chamber to reflect heat and to reduce wall radiation loss. The stove 

has been produced in 3 different sizes--small, medium and large. 

The Keren stove, a stove widely used in Central Java for boiling water 

and frying, is made of fired clay. It consists of a spherical firebox over 

which a pot is placed. There are 7 holes (1.5 cm in diameter) spaced evenly 

around the sides at the base of the firebox. The diameter of the firebox 

is 24 cm and the height is 16 cm. The enl:rance cf the firebox is 18 cm widL 

and 7 cm high. The stove weighs 3 kgs (Joseph eL al, 1980). 

The single pot ceramic Chula is found n many Asian countries. It is 

called Keren in Indonesia, Kamado cooker in Japan. This stove is usually 

cylindrical, approximately I cm in diameter and 10 cm in height, weighs 

about 5 kg and is easily portable. Fuel is added through a hole in the side 

at ground level. Wood, straw, dung, and other materials are burned as fuel. 

46

When charcoal is used as fuel, a grate is required (Foley and Moss, 1983). 

Tunga Sae, used in urban areas of Indonesia, is made from clay by a 

potter using either a pottery wheel and/or coiling techniques. It consists 

of a firebox, a connecting flue and a second pot seat. The connecting flue 

slopes up from the firebox and has a cross-section of 8 cm x 8 cm. The 

firebox has a height of 21 cm and a diameter of 24 cm. The second pot seat 

Las a height of 25 cm and a diameter of 20 cm. The stove weighs 8 kgs. 

Wood or wastes can be burned in this stove. When the first pot boils, it can 

be interchanged with the second pot to achieve faster cooking time and lower 

wood consumption. The first pot, now on the back hole, will simmer while 

the pot on the front is brought to boil (Joseph et al, 1980). 

A stove especially made for burning rice husk is used in Bali. It 

simply consists of an open-top oil drum with a hole in the side at ground 

level. Before loading it with rice husk, a thick stick is laid horizontally 

across the bottom of the drum from the center outward through the hole in 

the side. Another stick is held vertically at the center. The rice husk 

is then packed tightly around the two sticks. When a fire is required, the 

sticks are removed, leaving passage for air through the opeuing in the side, 

across the base, and up through the center of the fuel bed. The fire is 

kindled at the bottom, and provides approximately two hours burning (Cook 

Stoves Handbook, 1982). 

Recently, a company in the U.S.A. designed and constructed a portable 

stove, called the Z Stove (private communication). The stove is made of 

a pop-riveted, galvanized sheet steel box 7 x 7 inches square, 10 inches 

tall and 4 pounds in weight. The stove features a cylindrical firebox inside, 

with a galvanized screen fire grate at its bottom, an aperture for inserting 

bits of fuel, a small drawer beneath the grate for insertion of kindling, a 

draft/damper control, an X-type cooking vessel support and a wire bale 

handle. The stove can burn any solid fuel from wood to animal dung. The 

manufacturer claims that the stove is highly efficient. However, ITDG testing, 

showed that the Zip was 25.4 to 29.7% efficient (from Testing of the Zip Stoves, 

Stove Project Technical Notes No. 3). 

Fixed stoves 

Fixed stoves are usually constructed from mud, mud and clay bricks, or 

mud and sand. Collectively, these are often referred to as mud stoves, When 

constructed, these stoves are sometimes coated with a thin paste of cowdung 

to prevent them from cracking. 

In a simple fixed stove design, fire surrounds three sides with an 

opening for fuel at the front. It is built to take a single pot. The pot 

is sometimes seated on three or more small raised mounds around the pot hole. 

These permit the hot gases and smoke from the fire to escape upwards around 

the sides of the pot. In other cases the pot sits tightly into the pothole. 

In some rural areas of India, the opening for the fuel is bridged 

across to provide a complete surrounding for the bottom of the pot (Cook 

Stove Handbook, 1982). 

47

Many types of mud stoves have two or more potholes. Magan Choolah stoves 

in India are made from mud, dung or straw cuttings and cowdung. This stove 

has three potholes situated at the three corners of a triangle and 

interconnected by ducts. The hot gases pass ftom the first pot seat to the 

second, and then to the third. One damper is rositioned in the connecting 

duct between the first and second pot seat to control the rate of combustion. 

A chimney is incorporated as a smoke outlet (Tata, 1979). Similar mud stoves 

are found in the urban areas of Indonesia (de Lapeleire et al, 1981). 

A smokeless HERL Choolah stove was designed at the Hyderabad Engineering 

Research Laboratories in Hyderabad, India (Tata, 1979). It is made from 

bricks and mud or only mud. There are 4 pot seats situated on a L-S shaped 

duct, the first three are for cooking, the fourth is for heating water. One 

damper is positioned inside the connecting duct between the fourth pot 

seat and the chimney to control the rate of combustion. Only the first pot 

seat receives the maximum heat. When one or two pot seats are in use, the 

others are kept closed. 

In some mud stoves with two or more potholes, these potholes are 

positioned more or less symmetrically over the firing chamber and each pot 

obtains roughly the same amount of heat. One of these stoves is an improved 

HERL Choolah, which has three pot seats (Tata, 1979). A variety of forms 

(varying only in detail) are used in different parts of Indonesia (de 

Lapeleire et al, 1981; Singer, 1961). 

The Lorena mud stove which was developed at the Ahagui Experimental 

Station, Guatemala has five openings, for cooking and a chimney for smoke 

outlet (Tata, 1979; Kaufman, 1983). The first pct is heated directly by 

fuel; the others are heated by the hot gases which pass through a long system 

of ducts connecting one pot seat to others. There are three dampers: the 

first is in the duct that connects the mouth of the stove to the first pot 

seat; the second is between the second and the third pot seats; and the 

third is between the fourth and the fifth pot seats, 

B. STANDARD METHODS OF TESTING STOVE PERFORMANCE 

Although human being have been using biomass cooking stoves for a long 

time, standard methods of comparing stove performance evolved only recently. 

Joseph and Shanahan (1980) realized the necessity of standardizing testing 

methods; they found that improper stacking of wood could produce as much 

as a 100% in difference performance figures. 

A few methods of testing have been proposed (Joseph and Shanahan, 1980; 

Joseph, 1979). For a stove test to be useful, Joseph (1979) recommends that 

the test should be simple, reproducible, adaptable to any fuel stove, and 

reflect local cooking practices. It is found that neglecting the last 

recommendation can cause a poor stove performance when used with different 

practices (Joseph and Shanahan, 1980). 

In addition, Joseph (1979) suggests that the tests should be atle to 

determine the amount of energy used to cook a meal or boil water, and the 

amount of biomass fuel consumed. The reason for these two determinations 

48

is that the first will give the heat utilization or cooking efficiency, and 

the second the combustion efficiency. 

The performance of a stove is usually expressed in terms of heat 

utilization. This term is defined as "the ratio of heat absorbed by the 

water to heat liberated fL:om the burning biomass" (Joseph and Shanahan, 1980). 

There are two kinds of he.It utilization: one does not include the heat 

required in evaporating, the other includes the heat required in evaporating. 

Another term that is sometimes used in comparing stove performance is 

"burning rate". Burning rate is defined as the amount of wood (biomass) 

burnt (in the experiment) divided by the duration (of the experiment) 

(Joseph and Shanahan, 1980). The burning rates are found to vary with size 

of wood. 

Two types of tests are commonly cariied out on stoves: one is the 

"boiling water" test, and the other is the "cooking food". Other tests such 

as combustion tests are also sometimes used (Joseph, 1979). 

Boiling water tests 

There are 4 tests being used as standard methods: 

1. A fixed quanLi'v of water is evaporated, with fuel and time as 

variables. 

2. Quantities of fuel and water are fixed, with time as a variable. 

3. A fixed quantity of fuel is burnt, with the quantity of water 

evaporated and time as variables. 

4. The quantity of water evaporated within 30 minutes is determined, 

with fuel as a variable. 

Water boiling tests have been used by the Department of Applied Physics 

and Mechanical Engineering at Eindhoven University of Technology in the 

Netherlands, to study the performance of the Family Cooker and the De 

Lepeleire/Van Daele stove. 

Ponnoum et al.(1982) have used the boiling water tests in studying the 

performance of charcoal bucket stoves and wood stoves in Thailand. They 

found difficulty in identifying the time at which boiling started. 

Joseph et al.(1980) have developed another method of testing. They 

set the boiling time and vary the time for evaporation. For example, a 

pot of water takes a certain time, say "t" minutes, to boil. The water is 

then allowed to evaporate for 10, 20, 30, and 60 minutes. At the end of 

the experiment, the following measurements are recorded: 

" Weights of wood used and remaining and 

" 

The amount of water evaporated at each evaporating time. These 

measurements are then used to calculate heat utilization. 

49

Cooking food tests 

Simulated cooking tests measure the amount of fuel used and the time 

taken to cook a variety of standard meals under controlled conditions. The 

principle objective of the cooking test is then to determine the influence 

of the stove design on the amount of fuel used and time taken to cook a meal 

(Joseph and Shanahan, 1980). 

Cooking rice tests have been used by Pennoum et al.(1982) in 

investigating the performance of charcoal bucket stoves and wood stoves in 

Thailand. They measured the quantities of fuel, food, and water used. All 

the tests were performed with metal cooking vessels. Regular rice was 

placed in a pot and covered with water. The qua;city of rice and the ratio 

of water-to-rice was determined based cn household practices. The water and 

rice were brought to a boil. After a short period of time the excess water 

was poured off and the rice dried either over the fire or away from the 

fire. The rice cooking took from 25 to 40 minutes. 

One important point that must be stressed to investigators using this 

kind of test is that the tests should involve cookinp loca. dishes and that 

it is necessary to prepare the food in the same way for each test, using 

the same type of food. To obtain such information, a survey of the villagers' 

cooking habits must be performed. This approach has been carried out 

carefully by Pennoum et al.(1982) in their investigation of stove 

performance in Thailand. Designers also need to devise their own grading 

systems in collaboration with local women, to ascertai,. what the women 

regard as "cooked" food--for all the types of cooking (frying, baking, 

stewing, etc.). It is also important to get different village women to 

use the stove to cook these same meals and see if there is a change in the 

time taken and fuel wood used (Joseph, 1979). 

Steaming and open steaming are the two processes frequently used in 

cooking (Joseph, 1979). Steaming involves bringing water to boil and letting 

it evaporate. The steam then passes through the food. Some of the steam 

escapes and some condenses on the food and on the lid. If there is no food 

in the pot, the amount of heat required to totally evaporate the water is 

less than if there is food. Consequently, steaming of food cannot be 

simulated using only boiling water. In the case of open steaming, a small 

amount of food is placed in a relatively large pot of water, which is 

evaporated slowly. Most of the energy involved in the cooking process is 

used in the boiling and evaporating of water. Thus boiling water can 

simulate the process of slow open steaming. The simulation can also be 

applied to stewing. 

Combustion test 

In combustion tests (Joseph, 1979), gas analysis and measurement of the 

stack temperature were obtained. These data gave a measure of how much heat 

was being lost due to process combustion. According to this test, fuel is 

burning efficiently if: 

50

" The percentage of CO is less than 0.5%; 

" The average amount of oxygen in the flue gas is less than 11%; and 

" The average carbon dioxide content in the flue gas is approximately 

6-8%. 

Measurement of the chimney temperature, in the combustion test, indicates 

how much heat is being transferred to the pots. A high stack temperature 

means that the pots cannot absorb the amount of heat being liberated. As 

the temperature of gases decreases, the amount of air being drawn into the 

combustion chamber also decreases. 

C. FACTORS AFFECTING STOVE PERFORMANCE 

Problems that occur in the stove are classified and discussed below. 

Convective heat loss 

Convection is the mechanism by which gas moves up due to a difference 

in temperature. In stoves, convection can occur through the exhaust gap. 

When gas with a high temperature leaves the stove, it carries thermal energy 

with it. This energy is considered a loss. 

Wind promotes this mode of heat loss. An example is the open fire. 

Efficiency of an open fire drops in the windy condition since the fire is 

not protected. Efficiency can be improved by constructing a shield to 

protect the fire from the wind. It is found that the efficiency of an 

open fire stove increases to approximately 17 percent when the fire is moved 

into the kitchen (Vita News, 1984), 

In bucket stoves, it is found that stove efficiency can be increased 

by reducing the size of the exhaust area (Somzhai and Kanchana, 1983). The 

improvement is due to the reduction of convective heat loss through the gap. 

In stoves with many pot seats such as the Smokeless HERL Choolah. 

convection can be reduced by closing t,e seats that are not used (Tata, 1979). 

When all the seats are used, the convective loss is low since hot gases have 

to pass all the pot holes; hence, a higher proportion of the heat contained 

in them is usefully absorbed. 

Conductive heatloss 

Conductive heat loss occurs when the stove is not well insulated. Such 

loss is seen in the metal stove. To reduce this loss, the stove has to be 

insulated. However, thick insulation can also reduce stove performance 

during one or two hours of cooking, since massive walls absorb more heat 

than bare walls lose to the outside (Vita News, 1984). 

51

Radiative heat loss 

Since heat is transferred to the pot mainly by radiation, any loss due 

to radiation can affect stove efficiency. It is believed that radiative 

heat loss can occur through the exhaust gap (Somchai and Kanchana, 1983). 

Reducing the gap will decrease the radiative heat loss, and hence, impiove 

stove performance. In the case that the pot does not fit the pot seat, 

radiative heat loss is high. 

Size of fuel 

One of the problems affecting the comparison of stove performance (even 

when stoves and test conditions are standardized) is the size of the fuel 

used. It is found that the efficiency of the bucket stove increases when 

the size of the charcoal decreases (Somchai and Kauchana, 1983). 

Types of biomass 

There are many kinds of biomass fuel that can be used in stoves. They 

include wood, charcoal, and agricultural wastes such as rice husk. These 

fuels, when combusted, supply heat unequally. Chomcharn et al (1981) used 

the water boiling test to study the efficiency of a bucket stove fuelled by 

different types of charcoals, different firewood species, sawdust, rice 

husk, and lignite briquets. They found that the efficiency of the bucket 

stove varied with the fuel type used and ranged from 18.5 to 33.1%. 

Air supply 

Since the energy obtained in the stove is the energy from combustion, 

the degree of combustion strongly limits stove performance. There is no 

doubt that wood, which has a high heat of combustion, will poorly render 

heat under the conditions of insufficient supply or undersupply of air. On 

the other hand, if air is oversupplied, a certain amount of heat will be 

used in raising the temperature of excess air. This air then leaves the 

stove together with the exhaust gas. In this latter case, stove performance 

also decreases. 

Internal variables 

The initial project study that appeared in the interim report (Sherman 

and Bunyat, 1983) revealed that the internal variables of the charcoal 

stove(such as stove weight, grate hole area, exhaust area, air inlet area, 

and slope of the inner wall) strongly affect stove performance. 

Stove material 

As a stove caiibe made from either clay, cement, or metal, its 

efficiency varies. Openshaw (undated) compared metal and clay cooking 

stoves. He found that 40% of charcoal used could be saved by the household 

if the household used a clay stove instead of metal stove. In addition, the 

material chosen more or less reflects the long term service ability. 

52

D. CONCLUSION 

In the above review of the literature, it is apparent that there are 

many problems associated with biomass household cooking stove research, 

development and use. Therefore, before researchers embark on a stove 

development program they must first accommodate the mult4-faceted complex 

of problems of cooking stoves. Precognition of and distinctions between 

should be made regarding the following: 

" Stove types and kinds: chimneyed or non-chimneyed, single pot or 

multille pot holes, appropriate size to suit the need for individual 

or family in the working area. 

* Social nature or tradition of cooking: size of the family, normal 

duration of cooking time, low heat vs intense heat requirement, 

cuisine, extra services required from the stove besides cooking, etc. 

" Special requirements for stove users: speediness in cookiaig, ease 

of operation, reliability and consistency of stove performance, and 

the accommodation of various sizes and shapcs of pots, pans, and 

woks. 

" Materials and techniques for construction: inexpensive, locally 

available material vs expensive exotic material, simple construction 

vs complicated construction, and the stove's durability. 

" Fuel types and physical characteristics: charcoal, wood or agriresidues, 

fuel's forms in lump, long stick, chip, granule, dust, 

briquette and etc., fuel's moisture content, density, specific heat 

of combustion, soundness of the fuel, i.e. fresh or biodegradable. 

" Methods for testings and performance evaluations of cooking stoves: 

water boiling vs simulated food cooking tests, duration of tests, 

assignments of dependent and independent measuring criteria such as 

time, fuel load, water evaporated, etc. 

53

Chapter 3 

Plan and Design of the Project 

prwIaa

PLAN AND DESIGN OF THE PROJECT 

The project design aimed at: 

* Establishing a laboratory and facility to perform project tasks as 

well as for long-term stove improvement research and development; 

" Collecting existing local stoves for testing and evaluation; 

* Investigating existing stove performance; 

" Analyzing the physical factors of stoves that inhibit performance; 

" Developing an improved prototype; 

" Testing the prototype and its remodification; 

" Producing developed stoves; and 

" Promoting developed stoves in the field. 

A. LABORATORY AND FACILITY SET UP 

The project required an experimenting room for testing stove performance. 

An area of approximately 80 sq.m. was located behind the Forest Research 

Institute at the Royal Forest Department in Bangkok. The room consisted 

of space for storing the stoves, two large cement top counters for handling 

hot stoves during the testii.g, a sink with tap water for cleaning purposes, 

and an exhaust hood with ventilation fans fpr outletting the combustion 

smoke. All tests were conducted in this natural environment. 

The instruments applied to accompany the tests included: 3 weighing 

scales of different ranges from 500 gm, 7 kg, and 20 kg. 3 cromel/alumel 

thermo-couple and digital thermometers with a range of 0-800 °C for 

temperature measurement; bulk thermometer with a range of 0-100 'C; hygrometer 

for humidity measurement; electric oven for fuel drying; a series of 

aluminum cooking pots with sizes ranging from 16 cm to 32 cm; measuring 

tapes and calipers for dimensional measurements; and workshop tools. 

B. COLLECTION OF EXISTING LOCAL STOVES 

As previously mentioned, the three generic types of biomass cooking 

stoves (which consist of the charcoal stove, wood stove, and rice husk 

stove) were the main concern of the project for further development. The 

task of this phase was to collect as many of the various kinds (with various 

features) of these three types of stoves. Since biomass cooking stoves 

57

were widely distributed throughout the country, a stove collecting team was 

sent out to various locations to collect the stove samples and bring them 

back to the laboratory for testing. 

C. INVESTIGATION OF EXISTING STOVE PERFORMANCE 

Efficiencies of all collected stoves were evaluated using the same 

standard testing conditions which is described in the next chapter. All 

calculations based on data received from the stove testing were done on 

an IBM main frame computer at Kasetsart University. The results were 

analyzed closely for relevant relationships between the efficiency and the 

physical structure of the stoves. This information was critical for stove 

development. 

D. ANALYSES OF STOVE PHYSICAL FACTORS 

The stoves physical factors (such as section for air inlet, area for 

exhaust gas outlet, combustion chamber, grate, stove body, etc.) were 

analyzed. If one of these factors was changed so was the geometry of the 

stove. Such an effect was classified as an internal variable. There was 

another group of variables that had no effect on the geometry of the stove 

when their values changed (wind velocity, humidity, air temperature, pot 

size, etc.). This group made up the external variables. The effects of 

both the internal and external variables on the performance of stoves were 

studied. The understanding of their effects on the stove performance 

would be crucial in designing stoves with high efficiency. 

E. DEVELOPMENT OF IMPROVED PROTOTYPE 

When the order of most important variables chat affected the efficiency 

of the stove was determined from the test analysis, design of high 

efficiency stoves corresponding to the prominent variables was then 

accomplished. Technical drawings of thu stove prototype were made. 

After achieving the dusign of the stove prototype, the next step 

involved the selection of suitable quality stove materials, and, finally, 

construction of the stove prototype. Stove assembly closely followed the 

guidelines of the technical drawing. 

F. TESTING OF PROTOTYPE AND REMODIFICATION 

The finished stove sample was then subjected to the same efficiency 

tests. The results were compared with the existing stoves. This step 

might be carried out several times to assure that the developed stoves had 

reliable performance and high efficiency. 

58

G. PRODUCTION OF DEVELOPED STOVES 

Several manufacturers were selected for the production of the developed 

stoves. Guidelines and information were provided to the manufacturers to 

enoure consistency of the products made in large quantities. 

H. FTELD PROMOTION OF DEVELOPED STOVES 

The developed stoves were introduced to the public via mass media, 

schools, rural development organizations--both private and governmental. 

Relevant information for stove promotion was distributed in the form of 

pamphlets, manuals, brochures. Short term instruction on how to make, to 

select, and to properly operate various types of cookstoves that conserve 

wood and other biomass resources were also provided. Training of villagers, 

village leaders and rural development officers on the fabrication and 

selection of good stoves was also undertaken. 

59

Chapter 4 

Experimental Techniques and Procedures 

) 

• ,' (Q\

EXPERIMENTAL TECHNIQUES AND PROCEDURES 

This chapter will discuss the experimental techniques and ?rocedures 

involved in selecting and preparing fuels (firewood, charcoal, and rice husk), 

testing local existing cooking stoves, standard testing conditions, definition 

of heat utilization efficiency, and testing for the effects of the internal 

and external variables of charcoal and wood stoves. 

A. FUEL TYPE AND PREPARATION 

Besides having appropriate kinds of fuels for the three generic types 

of cooking stoves (namely, firewood, charcoal, and rice husk) preparation of 

the fuels was necessary to ready them for testing. Using fuels with varying 

characteristics can lead to inaccurate stove performance measurements. The 

following sections discuss the method of preparing the fuel by *ype of fuel. 

Firewood 

Firewood selected for the experiment was approximately 4 year old 

plantation grown Casuarinajunghuniana. The diameter was between 

2.5 - 7.5 cm. Each piece was then split laterally into 2 - 4 smaller pieces 

and sun-dried for several days. 

Charcoal 

In urban areas, charcoal is the most popular fuel for cooking. It 

burns withcut 6moke or smell and is thus suitable for indoor use. The 

charcoal used in the experiment wa.3 produced from plantation grown Rhizophora 

apiculata, a premium mangrove species for charcoal making. The selected 

species was approximately 10 - 12 years old and of a diameter of about 

2.5 - 5 cm, The process of firing the wood into charcoal occurred in standard 

commercial brick beehive kilns. 

Rice husk 

In the central area of Thailand, rice husk is often used for cooking. 

It is usually used in a rice husk stove. The cost of this fuel is very low. 

The rice husk used in the laboratory was obtained fresh from a 

commercial rice mill near Bangkok. It was dried later under laboratory 

conditions. 

The important characteristics of firewood, charcoal, and rice husk used 

in the experiment are summarized in Table 4.1. 

Fuels used in all of the experiments were acquired in large quantity and 

stored inside the test building under the same conditions. 

63

Table 4.1 Characteristics of Biomass Fuel Used in the Experiment 

Fuel Density Moisture content Heating value 

(gm/cm) (%) (MJ/kg) (Kcal/kg) 

Charcoal 0.78 3.5 - 5.0 26.34 6,300 

Wood 0.75 - 0.85 10.0 - 13.0 17.89 4,230 

(ave. 0.79) 

Rice husk 0.11 10.0 - 13.0 13.79 3,300 

B. TESTS OF EXISTING THAI COOKING STOVES 

Approximately 36 different types of charcoal bucket stoves, 39 wood 

stoves, and 5 rice husk stoves were brought back to the laboratory for 

performance evaluation. The physical dimensions of every stove were measured 

and recorded. These physical values were very important variables, and were 

used later in the analyses. All tests were performed by the Royal Forest 

Department staff. During each test run, combustion characteristics and stove 

behavior were observed clo-sely. The numerical, measured values of required 

information on water, ambient temperature, humidity, fuel weight, water 

weight, etc. were recorded on a data sheet. Efficiency for each test run 

was then evaluated, and the calculations were performed by an IBM mainframe 

computer at Kasetsart University. 

In order to study the performance and efficiency of various types of 

stoves, standard testing conditions need be followed. The procedure used 

in these experiments is summarized in the following section. 

64

Standard Testing Conditions 

All the tests were conducted under the following standard conditions: 

" Pot diameter: 24 cm (pot no. 24). (This pot size is commonly found 

in rural kitchens); 

* Wood kindling weight: 50 gm for wood stove, 30 gm for charcoal and 

rice husk stoves; 

" Fuel weight: for charcoal, use 400 gm, for wood and rice husk, 

feed in at normal rate as needed; 

" water weight: 3,700 gm. 

The pot is weighed and filled with 3,700 gm of water. The initial 

temperature of the water is controlled at 28 ± 10C, 50 gm of kindling is 

placed into the combustion chamber and ignited. About 30 seconds of lighting 

time should be sufficient to ensure that the kindling is ignited. The 

charcoal is then loaded onto the burning kindling. The pot is covered with 

a lid and is placed on the stove and the time is immediately recorded. The 

temperature of the water in the pot is measured every few minutes until the 

water starts to boil. Time required to bring the water from its initial 

state to the state of boiling is noted; the noted time is called "time to 

boil". Time to boil is one of the important variables which determine 

the characteristic performance of a cooking stove. 

When the water starts to boil, the lid is removed and boiling is 

continued for 30 minutes. After 30 minutes, any water remaining in the pot 

is reweighed as is any remaining fuel. The amount of water evaporated 

and the weight of the charcoal consumed in the test are then calculated. 

For wood and rice husk stcves, the test proccdures are carried out in the 

same manner. 

Stove efficiency is calculated from the data gathered in the procedure 

discussed above. The term "efficiency" will be used interchangeably with 

"heat utilization efficiency" in order to conform with the use of this word 

in other publications. 

Heat Utilization Efficiency (HU) 

The heat utilization efficiency (HU) is the percentage of actual energy 

transferred from potential energy stored in the fuel to the water in the pot. 

The equation for determining the HU value is adapted from Joseph (Joseph, 

1979). 

65

SX W (Tf - T) + (L x W) 

U, Z2 X 100 

x 

[(EfX Wf) + (EX W] (E W 

Where, S = Specific heat of water, 4.18 J/gm 

WM Weight of water in pot at start of test, 3,700 gm 

m 

Tf 2 Temperature of water at boiling point, 1000 C 

T a Temperature of water at start of test, 0 C 

L Latent heat of water at 1000 C, 2,256 J/gm 

W - Weight of water evaporated at end of each test, gm 

e 

Efm = heat value of fuel, J/gm 

Wf - Weight of fuel used, gm 

E - Heat value of wood kindling, J/gm 

Wk Weight of kindling, gm 

E - Heat value of charcoal, J/gm 

Co 

W = Weight of caarcoal remaining at end of each test, gm 

c 

C. TEST FOR ':HE EFFECT OF INTERNAL VARIABLE 

ON THE CHARCOAL BUCKET STOVE 

Most Thai bucket stoves have the following important physical features: 

* Stove gap/exhaust area; 

* Grate hole area; 

* Grate-to-pot distance; 

* Combustion chamber size; 

* Air inlet door; and 

* Crate thickness. 

66

The variation of one of the above characteristics is expected to have 

an impact on stove performance. These variables, moreover, are properties 

of the stove itself. Hence, they can be called the internal variables. 

To study the effect of one of the internal variables, it is necessary 

that the others are kept unchanged, or constant. The variable that is tested 

is varied in the range of its physical limit. Additional tests on a few 

more stoves may be required to confirm the effect of that variable on stove 

performance. This experimental technique was used in all project experiments. 

Stove Preparation for the Internal Variables Study 

Stove gap/exhaust area 

The stoves used in this study were stove nos. 1/5 and 1/31; their 

respective gap areas were 98.4 and 98.6 cm. For these two stoves, the time 

to boil and the charcoal consumption were experimentally determined; the HU 

values were subsequently calculatad. The gap areas of each stove was then 

reduced three times by adjusting the pot rest. The gap area tested on stove 

no. 1/5 was 86.1, 65.6, and 20.5 cm. The gap areas tested on stove no. 1/31 

were 86.0, 65.6 and 40.2. The stoves were retested for time to boil and 

charcoal consumption. 

Although the exhaust area did not appear in the equation for finding the 

HU value, it can indirectly affect stove performance. The exhaust area 

regulates the flow rate of the exhaust gas from the combustion chamber. As 

a consequence, the loss of heat, due to natural convection of gas through 

the gap, varies accordingly. For this reason, the exhaust area of the gap 

had to be considered as one factor that influenced stove performance. In 

this study, the gap area was reduced by adding clay to its width; this means 

that after the addition of clay, the length of the exhaust area is virtually 

unchanged. The variation of exhaust area, then, can be represented by the 

change in gap height. 

Total grate hole area 

Stove no. 1/5 was used in this experiment. The diameter of the grate 

was 15 cm, and the total grate area was 176.5 cm. The total grate hole area 

was 80.0 cm, 

To study the effect of grate hole area on stove performance, the grate 

hole area had to be varied by reducing the number of holes. The hole 

reduction was carried out by plugging the chosen holes with a rice husk 

ash and clay mixture. However, it should be kept in mind that the holes 

chosen to be filled up were distributed properly so that the inlet air, after 

reducing the grate hole area, was still distributed uniformly. 

Two tests using gap height as a parameter were performed to study the 

effect of the grate hole area on stove performance; both tests used stove 

no.1/5. The grate hole areas, with the above procedure, were set at 80.0, 

52.8 and 26.4 cm. The gap height of the stove was changed, using the method 

67

described in the above section on stove gap/exhaust area. It was 0°5 cm in 

the first test and 2.5 cm in the second. 

Grate-to-pot distance 

Grate-to-pot distance is defined as the distance measured from the 

surface of the grate to the pot bottom. This internal variable has a direct 

effect on stove performance; if the distance is small, the pot is iear the 

flame and stove performance is good--as would be expected. On the contrary, 

a large distance would render a poor stove performance. However, too small 

a distance will restrict charcoal loading and charcoal capacity. 

Stove no. 1/4 was used in this experiment. The grate-to-pot distance 

was varied from 7.5 cm to 9.3 cm and then to 11.0 cm. A distance of less 

than 7.5 is not recommended since the combustion chamber becomes too small 

to hold enough charcoal to cook a meal. Time to boil, the amount of water 

evaporated and the amount of charcoal consumed were all recorded. 

Combustion chcanber size 

The test for the effect of combustion chamber size on stove performance 

used three charcoal bucket stoves: stove nos. 1/28, l/A3, and l/Dl. The 

respective volumes of the combustion chamber were 4,216, 2,460, and 2.946 cm. 

After the first series of tests was completed, the volume of each stove's 

combustion chamber was reduced by increasing the lining thickness to 

3,414 cm (for stove no. 1/28), 1,787 cm (for stove no. 1/A3), and 1,510 cm 

(for stove no. I/Dl). All stoves were then subjected to the same test. 

Air inZet door 

Stove no. 1/5 was used to study the effect of the air inlet door area 

on its performance. The stove had a gap height of 1 cm and an air inlet 

door area of 66 cm. The area was later reduced to 49.5, 33.0, and 16.5 cm, 

which corresponded to 75, 50 and 25% of the initial area. The stove (as 

each door area was reduced) was tested for performance. 

Grate thickness 

Stove nos. l/E3 and I/E4 were tested for grate thickness. The grate 

thickness for both stoves was initially 2.0 cm and was later changed to 

3.6 cm. At these two grate thicknesses, the test for the efficiency was 

performed. 

D. TEST FOR THE EFFECT OF EXTERNAL VARIABLES OF THE 

CHARCOAL BUCKET STOVE 

In the previous section, the internal variables--the properties of the 

stove--were discussed. There is another group of variables that can affect 

the performance of the stove, but they are not the properties of the stove 

itself. The variables in this group are called the external variables. 

Examples of them are; 

68

* Initial weight of charcoal; 

e Initial weight of water; 

* Pot size; 

e Charcoal size; 

e Wind effect; and 

* Humidity effect. 

To study the effects of the external variables (pot size, charcoal size, 

wind and humidity) a laboratory test was conducted, using the same testing 

procedure described in this chapter in the section on Standard Testing 

Conditions. For the initial weight of charcoal and the initial weight of 

water, the other two external variables, one of them is varied at a time. 

Stove Preparation for the External Variable Study 

The external variable experiments tested the initial weight of charcoal, 

the initial weight of water, the pot size, the charcoal size, the wind effect, 

and the humidity effect. Procedures are discussed below. 

Initial weight of charcoal 

Stove no. 1/5 was used in this experiment. The first test for stove 

performance was performed with the initial weight of charcoal at 300 kg and 

the initial weight of water at 2,300 kg. 

The experiments were then repeated, keeping the same initial weight of 

water, but changing the initial weight of the charcoal to 350 and 450 gm. 

The above procedure was repeated with the initial weights of water set 

at 3,000 and 3,700 gm. The results obtained from the experiments were used 

in calculating the HU values of the stove. 

Initial weight of water 

The experimental technique for this study was described in the 

last section. The data is analyzed to obtain effect of initial weight of 

water on stove performance. 

Pot size 

Stove nos. 1/4 and l/E3 were used in this experiment. Three different 

pots with diameters of 24, 28, and 32 cm were used. The test was carried 

out under standard conditions. 

69

CharcoaZ size 

In order to study the effect of charcoal size on stove efficiency, a 

long piece of charcoal (an approximately uniform cross section) was cut 

into pieces. These were then used in the experiment. The term "size", in 

fact, refers to the length of the charcoal. In this test, two different 

lengths of charcoal were used: 2.54, and 10.16 cm. Stove nos. 1/5, 1/12, 

1/14 and 1/20 were used in the test. 

Wind effect 

Stove nos. 1/2, 1/5, 1/17, and 1/20 were used to test the effect of 

wind. Wind was induced by an electric fan; the speed was measured by an 

anemometer. The tests were first performed without turning on the fan; this 

represents the condition without wind effect--the reference condition. 

Later, the tests were repeated with the fan on. The wind speed for stove 

nos. 1/2, 1/5, 1/17 as measured was 80 m/min, and for stove no. 1/20 was 

86.7 m/min. 

Humidity 

Stove no. 1/5 was used in the experiment. The humidity of the 

experimenting room was measured by a psychrometer (wet and dry bulb thermometers). 

In order to test the stove under an environment of varying 

humidity the test was performed at various times of day and in different 

seasons. The percentages of humidity recorded on six experimental days were 

68, 74, 76, 78, 80, and 92. 

E. TEST FOR THE EFFECT OF VARIABLES ON THE 

NON-CHIMNEYED WOOD STOVE 

Similar to the charcoal bucket stove, the internal variables being 

studied include: 

9 Stove gap/exhaust area; 

9 Grate hole area; 

e Grate-to-pot distance; 

* Air inlet door; and 

e Ratio of exhaust area to grate hole area. 

The variation of one of the above characteristics is expected to 

affect the performance of the wood stove in a manner similar to that of the 

charcoal stove. 

70

Stove Preparation for the Internal Variables Study 

Stove gap/exhaust area 

Twenty-two wood stoves, having different gap areas and being made by 

different manufacturers, were tested for the effect of the gap on stove 

performance. The gap heights ranged from 1 to 3.0 cm. Each stove was tested 

at least three times. Time to boil was recorded, and the HU values were 

calculated from the difference between the amounts of wood initially put into 

and left in the stove. 

Total grate hole area 

To investigate the impact of the grate hole area on stove performance, 

wood stoves from various sources were used. The stoves were divided into 

3 gro:tps according to the number and the size of the grate holes. Group A 

had 37 grate holes with a diameter of 2.5 cm; in group B, the hole was 

1.5 cm in diameter, ard the total number of holes was 90; group C had 61 

holes, each of which was 1.23 cm in diameter. Every stove in the test had 

the same grate-to-pot distance of 12 cm. 


More than twenty wood stoves were used to study the effect of grate-topot 

distance on stove performance. The distance ranged from 9 to 17.5 cm. 

The stoves were again obtained from different manufacturers. Each stove 

was tested at least three times. 

Air inlet door 

The impact of the air inlet door on stove performance was studied with 

the wood stoves having door open at first and closed later. Each stove was 

tested at least three times. Time to boil and HU value were then calculated. 

F. TEST FOR THE EF}'ECT OF EXTERNAL VARIABLES OF THE 

NON-CHIMNEYED WOOD STOVES 

Only the effect of wind velocity and fuel feeding rate were studied. 

Stove Preparation for the External Variables Study 

Wind effect 

The effect of wind on stove performance was studied. Three stoves 

were used in this investigation; each was run at least three times under 

two conditions--with and without wind. Wind was induced by an electric 

fan. The wood stoves came from differen. manufacturers. Time to boil 

was noted and the HU values were calculated. 

71

Fuel feeding rate 

In this Lest, the wood was fed into the stove at different rates. The 

rate was measured along with the weight of wood, since wood was put into 

the stove at regular intervals Three rates were studied, labelled low, 

medium and high. The tests were performed using two wood stoves, one with 

a grate height of 12 cm and the other with a grate height of 15 cm. The 

weights of wood for the low, medium and high rates were 0.84 kg, 1.00 kg, 

and 1.21 kg, respectively, for the first stove. The weights of wood for 

the second stove were 1.31, 1.53, 1.75 kg, which reflect the low, medium, 

and high rates of fuel feeding, respectively. 

G. TEST FOR THE EFFECT OF INTERNAL VARIABLES ON 

CHIMNEYED WOOD STOVE 

Stove performance tests were conducted on three wood stoves with a 

chimney. They wer used to test the effect of chimney materials, metal ring 

around the pot hole and the baffle. No external variables were investigated. 

Stove Preparation for the Internal Variable Study 

Metal ring around pot hole 

Performance of wood stove no. 2/11 was measured for the effect of the 

metal ring around the pothole. The stove initially had a metal ring. After 

it had been tested, the ring was then removed. The stove was then retested. 

All the necessary data for comparing efficiency were recorded. 

Chimney material 

To study the effect of chimney material on stove performance, stove 

no. 2/12 was used. The stove was first tested as initially constructed. 

Later, the chimney material was changed to iron, and the stove was then 

retested. The material was changed again to cement and another test was 

performed. Data were recorded under each condition. 

Baffle 

Stove no. 2/12 (the same stove used to investigate the effect of chimney 

material) has no baffle between the firing chamber and the chimney; therefore, 

it was used to study the effect of a baffle on stove performance. Two 

kinds of baftles were examined: one made of fire clay and the other made of 

iron. The iron baffle was tested first. The standard test was then applied 

to estimate stove efficiency. The iron baffle was then replaced by a fire 

clay baffle and the te-st was repeated. 

72

H. TEST FOR THE EFFECT OF INTERNAL VARIABLES ON 

CHIMNEYED RICE HUSK STOVE 

Four internal variables were investigated for their effects on the 

performance of the chimneyed rice husk stove. They were the fuel gas outlet 

area, base-to-pot distance, firing chamber, and chimney height. 


Fuel gas outlet area 

A chimneyed wood stove was used to study the effect of the fuel gas 

outlet area on stove performance. The initial outlet area of the stove was 

95.0 sq cm. This area was reduced by adding clay to the outlet in the 

second and the third runs; the areas were 47.0 and 38.0 sq cm, respectively. 

In each case, time to boil and amount of fuel used were recorded. 

Base-to-pot distance 

To study the effect of base-to-pot distance on the performance of the 

chimneyed wood stove, stoves with different distances were used, In the 

test, the distances were varied from 18.0 to 36.0 cm. Each stove was tested 

at least 3 times. Data on time to boil and amount of fuel used were collected. 

Firingchamber 

The effect of the firing chamber on stove performance was studied by 

varying the size of the chamber. This was done by adding clay to the 

chamber to reduce its volume. The initial size of the firing chamber was 

16,600 cu cm; it was then reduced 3 times. The volume became 16,400, 

12,600, and 12,400 cu cm, respectively. Data were collected for time to 

boil and amount of fuel used. 

Chimney height 

The chimney height is another parameter that affects the performance 

of the stove, since height causes change in the rate of exhaust outflow. 

To study this effect, the chimney of a stove was decreased from 230 to 200 cm. 

Time to boil and amount of fuel used before and after reducing chimney height 

were recorded. 

I. TEST FOR THE EFFECT OF INTERNAL VARIABLES ON 

NON-CHIMNEYED RICE HUSK STOVE 

Since there are many kinds of non-chimneyed rice husk st'ves, testing 

all the stoves marketed would have been tedious. Only one stove design was 

chosen as the representative of non-chimneyed rice husk stoves. This stove 

was designed by Mr. Meechai. 

73

The Meechai stove consists of 2 parts -- the outer cone and the 

inner cylinder. For the outer cone, the following parameters were 

studied: height, upper diameter, lower diameter, slope angle of cone, 

and number of air inlet holes. For the inner cylinder, the effects of 

height, exhaust area, and fuel flow area were investigated. The dimensions 

of the reference Meechai stove are as follows: 

Outer cone 

Inner cylinder 

Height 37.0 cm. 

Upper diameter 46.0 cm. 

Lower diameter 8.0 cm. 

Slope angle of cone 63.0 deg. 

Number of air inlet holes 329 

Diameter 16.0 cm. 

Exhaust area 184.0 sq cm. 

Fuel flow area 163 sq cm. 


Height of the outer cone 

Four Meechai stoves were used to study the effect of the height of the 

outer cone on stove performance. The heights were 30.5, 33, 37.0, and 

47.0 cm. Time to boil and amount of fuel used were recorded. 

Upper diameter of the outer cone 

To investigate the impact of the upper diameter of the outer cone on 

Meechai stove performance, three stoves were used. The diameters of the 

stoves were 46.0, 43.0, and 41.0 cm. 

Lower diameter of outer cone 

Three stoves were used to study the effect of the lower diameter of the 

outer cpne on stove efficiency. These stoves had diameters of 8.0, 9.0, 

10.9 cm, respectively. The water bciling test was used to compare stove 

efficiency. Time to boil and amount of fuel used were noted. 

74

Nwnber of air inlet holes 

The Meechai stove is similar to other types of stoves in that air inlet 

holes control the supply of fresh air to combustion. 

air inlet holes has some impact on stove performance. 

used stoves with the following numbers of holes: 331 

was tested at least 4 times. 

Height of inner cylinder 

Indeed, the number of 

The investigation 

and 274. Each stove 

The inner cylinder contains the firing chamber. As a consequence, the 

height of the cylinder was expected to affect stove performance. Only three 

stoves were used in the study. Each was tested at least 5 times. The 

heights of these three stoves were 16.0, 19.0, 20.0 cm. 

Exhaust area 

To investigate the effect of the exhaust area, four stoves were subjected 

to the test. The exhausc areas were 184, 165, 129, 123 sq cm, respectively. 

Fuel flow area 

Rice husk in Meechai stove has two roles--it is used as fuel, and it 

insulates the stove. The insulating rice husk, which is situated in the 

space between the inner cylinder and the outer cone, sooner or later becomes 

fuel for combustion. Thus, the fuel flow area should control the fuel 

supply to the stove. To verify this hypothesis, four stoves with the fuel 

flow areas of 163 and 184 sq cm were tested. Each stove was run at least 

two times. Data on time to boil and amount of fuel consumed were recorded. 

J. DEVELOPMENT OF IMPROVED STOVE PROTOTYPE 

Using the techniques outlined in the previous sections, the effects of 

both internal and external variables on stove performance were studied. The 

results were then used to design a high performance stove. To achieve this 

end, all the internal variables had to be analysed carefully. The analysis 

indicated which factors contributed significantly to stove performance. 

Five prototypes of different stoves were developed; they were prototypes 

of a charcoal stove, a wood stove with and without chimney, and a rice husk 

stove with and witbout a chimney. These prototypes were then tested to 

ensure high performance prior to commissioning persons to produce the stove 

in quantity fo- trial promotion. 

75

Chapter 5 

Analysis of Results and Discussion

ANALYSIS OF RESULTS AND DISCUSSION 

This chapter analyzes the measured values of the physical structure of 

commercial stoves. Performance and characteristics of tested commercial 

stoves are evaluated and discussed. An intensive analysis of the internal 

and external variables affecting commercial charcoal and non-chimneyed wood 

stoves performance is presented in the chapter. 

A. PHYSICAL STRUCTURE OF COMMERCIAL STOVES 

Of the five types of biomass cooking stves already mentioned, the 

commercial charcoal bucket stove and the wood bucket stove without chimney 

are the most popular in Bangkok and urban areas. Their structure consists 

of an inverted truncated cone made of fired clay placed inside the metal 

sheet bucket. The prominent component parts of both charcoal and wood bucket 

stoves that may influence the stove's behavior are: pothole diameter, 

size of fuel firing chamber, grate diameter, grate hole area, grate thickness, 

grate-to-pot distance, exhausted gap, stove wall thickness, and air inlet 

area. Most bucket stoves are insulated with a mixture of rice husk ash and 

clay. Since the fuel feeding method of a wood stove differs from that of 

a charcoal stove, the wood stove includes a small removable feeding port 

above the air inlet door. In practice, this bucket wood stove is often 

used for charcoal fuel also. 

While the structures of the bucket stove for charcoal and wood use in 

urban areas are similar, the physical appearance of the wood stove in rural 

areas may vary from place to place. Some wood stoves are shaped like a dome, 

some like a horseshoe, an enclosed horse shoe, a pit in the ground and three 

stones; almost none have any insulation or grates. 

The measured physical dimensions of charcoal and non-chimneyed wood 

stoves are shown in Table 5.1 and Table 5.2. Since their shapes are so 

diverse, the appearance of each iidividual stove is fully displayed by the 

photographs in Annex I and II at the end of this report. 

For wood stoves with chimneys, there are three distinct models, namely 

Saeng Pen, Samrong, and Banpong. Their physical configurations can be seen 

in Annex III. The main structural components cf this stove are much the 

same as those of the wood stove without chimney, except for a fuel gas outlet 

port with connected chimney located at the opposite side of the fuel feeding 

port. The dimensions of the fuel gas outlet area and the chimney as well 

as other important structures are listed in Table 5.3. 

For the rice husk stove without chimney, the only practical type found 

is used by the Kampuchean refugees in Khao-I-Dang camp and is called the 

"Meechai Stove". (See the photograph in Chapter 7). This kind of rice 

husk stove was constructed from a rough drawing at the RFD workshop and was 

tested for performance. Its main features consist of an outside fuel 

receptacle cone and an inner combustion cylinder. Between these two parts

Table 5.1 Physical dimensions of tested charcoal stoves 

Code Name/source Stove Pot hole Firinq Grate Grate Exhaust Ave.wall Air inlet 

no. -t -diameter chamber dia hole no.of hole thickness to pot oap area thickness area 

(cm) (cm) (cm ) (cm) dia hole area (cm) (cm) (c=) (cm 2 

, (cm) (cm 2 

) 

(cm) (cm 2 

) 

1/2 Rangsit 12.2 19.0 2426 17.5 1 .3 85 112.0 4.0 12.0 2.0 96.0 5.8 70.0 

1/3 Rangsit 8.7* 19.0 2426 17.7 1.3 85 112.0 3.5 12.0 1.8 97.0 4.1 70.0 

1/4 Ranosit 12.8 19.0 2426 17.5 1.3 85 112.0 4.0 1Z.? 1.5 76.0 5.9 70.0 

I/5 Rangsit(atainless case) 9.3 16.0 1575 11.0 1.3 61 80.0 3.5 12.0 1.0 41.0 5.7 66.0 

1/6 Rangsait 8.6 20.0 2065 !5.5 1.2 61 69.0 3.5 12.0 1 .0 41.0 5.8 66.0 

1/7 Ayudthava 6.4 21.0 1931 19.0 2.1 19 66.0 3.5 12.0 1.0 41.0 5.8 66.0 

1/8 Unknown 8.1 18.0 1831 17.5 1.8 19 48.0 1.8 6.5 2.0 68.0 3.8 60.0 

1/9 Chachoenosao 8.1 18.0 1832 15.7 1.8 19 48.0 2.0 9.0 1.5 70.0 5.4 55.0 

CD 1/10 Unknow 6.6 21.0 2475 18.5 2.4 19 86.0 1.8 8.0 1.0 90.0 3.4 66.0 

1 /11 Unknown 4.3 20.0 2176 18.0 1.6 27 54.0 1.6 10.0 2.0 80.0 2.2 58.0 

1/12 Booopararm 7.2 21. 2856 19.5 1.5 37 65.0 1.6 10.0 2.0 80.0 2.2 58.0 

1/13 Samvakohichal 10.7 22.0 2390 18.5 1.9 27 96.0 1.8 10.0 1.6 74.0 6.2 48.0 

1/14 Booopararm 19.0 20.0 3464 19.0 1.5 37 65.0 2.0 11.0 2.5 113.0 6.1 60.0 

l.'.- Banolane 10.0 20.0 2865 19.0 1.5 36 65.0 1.2 9.0 2.0 108.0 6.0 76.0 

1 16 Ayudtha.ya 6.7 21.0 2618 14.5 2.0 19 59.0 2.0 7.5 1.0 45.0 3.4 66.0 

1/17 Cholburi 5.9 17.0 2013 15.0 1.6 27 54.0 1.5 10.4 1 .2 50.0 4.7 60.0

Table 5.1 (continued) 

Code Name/source Stove Pot hole Firing Grate Grate Exhaust AveWall Air inlet 

no. wt 

(cm) 

diameter 

(cm) 

chamber 

(cm 3 

) 

die 

(cm) 

hole 

die 

no.of 

hole 

hole 

area 

2 

(cm) (cm ) 

thickness 

(cm) 

to pot 

(cm, 

oap 

(cml 

area 

(cm 2 

) 

thickness 

1/18 Cholburi 7.2 21.0 3202 18.5 1 .8 27 68.0 1.9 11.0 2.0 96.0 3.9 70.0 

1/19 Samrono 10.5 18.0 3042 15.5 1 .8 37 94.0 1.8 11.0 2.5 101.0 6.3 70.0 

1/20 Cholburi 10.2 23.0 2516 20.0 ( .8 37 94.0 1.9 7.0 2.0 102.0 5.3 70.0 

I-, Darnkvian 11.1 22.5 2414 20.0 1.8 27 68.0 (.8 9.0 3.0 107;.0 4.5 80.0 

1/22 anpong 9.5 20.0 3155 18.5 1.5 48 85.0 2.5 11.0 0.8 38 3.4 80.0 

1/23 Raegsit 7.2 16.0 1575 15.0 1.3 61 80.0 3.9 12.0 1.0 41.0 4.2 66.0 

1/24 Cholburi 13.8 22.0 3815 10.5 1.9 27 77.0 2.2 11 .0 2.2 112 6.1 108.0 

1/25 Rangsit 13.2 19.0 2426 27.0 1.3 85 112.0 4.0 9.0 2.0 96.0 6.2 70.0 

1/26 Darnkwian 6.6' 23.0 2700 20.0 (.8 30 75.0 1.6 9.5 1.5 90.0 2.9 86.0 

1/28 Sa-Sua 12.2 23.0 4216 20.0 1.6 37 74.0 2.2 10.0 2.3 131.0 4.5 124.0 

1/29 Sa-Sua 13.3 19.0 3414 17.0 1.6 37 74.0 2.0 11.5 2.0 85.0 4.8 124.0 

1/30 Nakornchaisri 18.0 20.0 2992 19.0 1 .5 73 131 3.5 12.0 2.0 102 3.7 127.0 

1/31 Nekornchaisri 11.8 17.0 2250 16.5 1.4 61 94.0 3.0 12.0 0.5 20.0 -6.2 88.0 

1/32 Nakorncheisri 8.2 20.0 2992 19.0 1.5 73 131 3.5 12.0 2.0 102.0 3.7 127.0 

1/33 Nakornchaisri 6 7. 17.0 2550 17.0 1.4 61 94.0 3.0 12.0 0.5 20.0 3.8 88.0 

1/34 Bangsue 10.0 20.0 2829 18.0 1.8 27 68.0 1.5 9.0 .8 103.0 6.3 105.0 

1/35 Ban.sue 8.0 17.0 2176 16.0 1.6 27 54.0 1.6 11.0 1.7 82.0 5.6 81.0 

1/26 Bangsue 6.5 15.0 1568 13.5 1.7 19 44.0 * .6 9.5 1.9 56.0 6.2 75.0 

1/37 BooPpararm 6.5 15.0 1130 13.0 1.3 19 25.0 1.6 -9.0 0.7 60.0 4.6 38.0 

1/38 Unknown 10.0 19.0 2000 16.0 1.0 89 70.0 1.9 10.0 1.9 122.0 4.2 66.0 

fNaked stove without insulation and bucket. 

(cm) 

area 

(cm 2

Table 5.2 Physical dimensions of tested wood stoves without chimney 

Code Name/ourte Stove Stove Pot hole Firing Grate Grate/bese txnaust Wall Pri -ary Feedin 

no. -t ht diameter chamber dia hole no.of hole to pot oac area thicxness air tor: port 

(cm) (cm) (qa) (cm3 (cm) dia hole area (cm Ic.; (c 2 

2 

(cm) (cm ) 

) (cml (cm ( 2 

) 

1/2 Rangsit 12.2 27.0 19.0 2426 17.5 1 .3 35 112.0 12.0 2.0 36.0 6.0 70.0 54.0 

1/8 Unknown 8.1 18.5 18.0 1832 17.5 1 .8 19 48.0 9.0 1 .5 70.0 5.4 75.0 55.0 

1/9 Chachoenc-ao e.7 2-.0 23.0 3232 20.5 1 .8 37 94.0 6.5 2-.0 62.0 4.8 90.0 57.9 

1/12 Ecoooararm 7.2 22.5 21.0 2851 19.5 1 .5 37 65.0 9.0 2.0 80.0 4.6 118.0 60.0 

1/13 Samakohichai 10.9 18.0 22.0 2390 18.5 1 .9 27 76.0 10.0 1 .6 74.0 6.2 48.0 44.0 

1/19 Samronge 18.0 16.5 18.0 3040 15.5 1 .8 27 94.0 11.0 2.5 101.0 6.3 70.0 56.3 

1:20 -holburi 10.2 24.0 22.0 2516 20.0 1 .8 37 94.0 7.0 2.0 102.0 5.3 70.0 13.7 

1/21 Darnkwian 11.4 30.0 22.5 2414 20.0 1.8 27 68.0 9.0 2,.0 107.0 4.5 34.5 80.0 

1/24 :holbur- 13.8 27.0 22.0 3815 20.5 1.9 27 77.0 11.0 2.: 112.0 6.1 10E.0 224.0 

1,'25 Rangsit 12.2 30.0 19.0 2426 27.0 1 .3 85 112.0 9.0 2.0 96.0 6.0 78.0 81.3 

2 11 Roi-et (oricinall 5.9 21.C 22.0 7600. no grate 20.9 1 .3 25.3 2.0 - 296.4 

2/2 Thick dome, tIay 11.8 14.8 22.0 5800 14.3 2.1 162.0 7.0 - 181.5 

2.:3 Thick horse shce. clay 18.2 15.3 25.0 £870 1. .4 8S.3 6.0 - 225.0 

2'4 morn PaKred, mt ,ied 2.5 12.0 27.0 7440 24.5 1.5 90 160.9 12.0 2.5 90.7 1.7 20.0 243.0 

2'5 .rn Pa5e, s.ca: I 

2.6 12.0 18.0 3600 - no grate - 14.0 5.0 210.0 2.0 - 280.0

Table 5.2 (continued) 

Code Name/source Stove Stove Pot hole Firing Grate Grate/base Exhaust wall Primary Feeding 

no. wt ht diameter chamber dia hole no.of hole to pot qap area thickness air port port 

(cm) (cM) (cm) (cm ) (cm) dia hole area (cm) (c--) (cm 2 

) [ c2 (. 2 ) 

(cm) (cm 2 

) 

2/6 Tripod 0.9 14.0 2C.0 4080 no grate 14.0 - - - - 82.0 

2/7 Morn Pakrad, larae 3.3 14.0 27.0 7440 - 14.0 5.4 222.6 2.0 - 332.0 

2/8 Modified Ro±-et, clay 6.6 15.0 22.0 4560 14.8 1.0 55.5 3.8 - 204.3 

2/9 Norse shoe, clay 8.1 13.4 25.0 6380 - 11.5 2.5 197.1 5.5 - 208.0 

2/10 Thin horse shoe, clay 7.4 14.0 22.0 4560 12.0 3.6 77.6 3.8 - 325.0 

2/13 Dome, clay 9.3 15.0 24.0 5400 24.5 1.5 9:.O 160.9 14.5 1.3 62.4 4.0 60.0 175.0 

2/16 Pot shaoed, clay 10.3 18.5 22.0 7030 1 no grate 18.0 1.8 86.4 5.0 - 157.5 

2/22 Dome with cap, clay 11.3 18.7 22.0 6840 24.5 1.5 91.0 160.9 17.2 1.5 73.1 3.3 76.0 202.0 

2/23 odified Roi-It. clay 14.0 19.0 24.5 4950 24.5 1.5 910 160.9 12.2 1.8 86.6 3.5 115.0 114.0 

2/24 Cylinder, steel 3.7 17.0 17.0 2040 23.4 1.2 89.0 99.6 13.0 0.6 32.2 1.8 42.0 94.5 

Note stove 1/2 -1/25 are nf the bucket type asid 2/1 - 2/24 are the non-bucket

Table 5.3 Physical dimensions of tested wood stoves with chimney 

Code flaei Source StD'e st-Ve Pot hcle Firin. Grate Grate Flue cas A.e.'all n.ir- - i.-no Chimney 

no. "t nt diameter thamner die hole no.of hole to pot out'et thicktness air port Dart hr 

(-) (cm) (Cm, (crn ) (cm) Icm) hole area cm) 

[c 2) 

c.-; (c 

2 

c" (CM) 

2/11 Saenq Pen 24.S 235 19.0 5190 22.0 2.0 22 72.2 17.0 75.2 4.3 34.0 20.3 71.0 

2/12 Sarc'onq 24-3 3:-5 20.9 4400 20.5 0.5 3. 65.4 1".0 22.5 4.2 185.7 11! .r 80.0 

2/15 BarDonq -5 25.3 29.0 5890 24.5 2.0 30.3 44.3 12.0 22.A ".0 216.0 24:.) 230.0

there is a gap through which the rice husk flows. The slope of the outside 

cone plays an important role in facilitating the rice husk's slide to the 

combustion zone. The combustion air is drawn in through the punched holes 

evenly distributed oilthe lower part of the outer cone wall. A list of the 

physical dimensions of rice husk stoves without chimneys is shown in Table 

5.4. 

For rice husk stoves with chimneys, five recognizable makes are found, 

namely Ngo Gew Ha of Lamlooka, Thai Charoen of Rangsit, Takeseng of 

Banglane, Sayun of Samrong, and Sooksunt of Dhonburi. The rice husk stoves 

are made of either cement or fired clay. They are quite heavy, a factor 

decreasing their popularity. The prominent features of this type of stove 

include a pothole, firing chamber, grate, air inlet port, fuel gas outlet 

port, chimney, ash removed port, and stove high mass body. The physical 

dimensions of the five stoves described above are measured and presented 

in Table 5.5. Photographs of these stoves are shown in Annex IV. 

B. TERMINOLOGY 

For clarity, the terminology used for describing the features of each 

type of stove is presented in Fig. 7.1 to 7.5 in Chapter 7. 

C. PERFORMANCE OF COMMERCIAL STOVES TESTED 

The performance of the charcoal stove, wood stove with and without 

chimneys and rice husk stoves with and without chimneys is discussed as 

follows: 

Charcoal Stove 

The results of 34 commercial stove performance tests shown in Table 5.6 

indicate that their efficiencies vary from 23% - 32%. The time to bring 

water from the iiritial controlled temperature to the boiling point varies 

from approximately 17 minutes - 32 minutes. The rate of fuel consumption or 

burning rate varies from about 6 gm/min to nearly 8 gm/min Fig. 5.1 and 

Fig. 5.2 show the plotted values between the individual stove and its 

efficiency and the stove and its time to boil. 

The stoves with high efficiency (such as stove no. 31, 17, 36, 5 and 

33) have shown a prominent effect on the rate of bringing water temperature 

to boiling. That is, the time to boil of a group of high efficiency or good 

stoves is shorter than a group of low effieicney or poor stoves. 

Time-temperature characteristic curves of poor and good charcoal stoves 

are shown in Fig. 5.0. 

85

Table 5.4 Physical dimensions of rice husk stoves without chimney 

Code 

no. 

Outer cone 

Upper Lower 

diameter diameter 

(cm.) (cm.) 

height 

(cm.) 

Air inlet 

No. 6, cm. 

Insulation 

Inner cylinder 

PExhaus,-d 

Iame ter tIeight area 

(cm.) (cm.) (cm) 

Fuel flow gap 

area 

cm) 

A 46.0 8.0 37.0 329 0.6 no 21.0 16.0 184.0 163.0 

B 46.0 8.0 37.0 329 0.6 yes 21,0 16.0 165.0 163.0 

C 43.0 9.0 30.5 331 0.6 yes 21.0 16.0 165.0 163.0 

D 43.0 9.0 30.5 331 0.6 yes 21.0 20.0 129.0 184.0 

£ 43.0 9.0 30.5 331 0.6 yea 21.0 16.0 184.0 163.0 

F 43.0 9.0 30.5 274 0.9 yes 21.0 19.0 123.0 163.0 

0 41.0 10 33.0 274 0.9 yes 21.0 19.0 123.0 163.0 

F) 41.0 10 33.0 274 0.9 no 21.0 16.0 165.0 163.0 

1 41.0 10 33.0 274 0.9 no 21.0 20.0 129.0 184.0 

86

Table 5.5 Physical dimensions of rice husk stoves with chimney 

Code Name/scure Stove Stove Pot hole Firing Grate Air inlet Flue gas Chi.mtney Base to pot 

I". ht diameter chamber slooe area outle- area ht distan=e 

( . (cm) (cm) (cm3 (cm2 (cm2) (cm) (cm) 

3/2 Nc Ge, Ia e5.o 38.0 32.0 19,000 45 490.0 78.0 240.0 29.0 

3/3 Thai tnaroen 96.0 39.0 21.0 17,100 47 420.0 78.0 240.0 29.0 

3/4 Thai :aroen 96.0 29.0 32.0 16,600 44 442.0 95.0 240.0 26.0 

3/4A1 Thai Charven 96.7 39.0 33.0 16,400 44 442.0 47.0 240.0 26.0 

3/4A3 Thai Charoen 96.7 39.0 33.0 16.400 44 442.0 95.0 240.0 26.0 

3/480 Thai Charo-n 94 .0 39.0 '3.0 12,600 44 442.0 95.0 240.0 26.0 

0o 

4 3/482 Thal Charven 96.0 39.0 33.0 12.400 44 442.0 38.0 240.0 26.0 

3/5 Banolane 95.5 59.0 30.0 19,100 40 723.0 113.0 230.0 36.0 

3/5A Sanolane 95-5 S.u 30.0 19,100 40 703.0 113.0 200.0 36.0 

3/5I Banalane 95-5 59.0 30.0 19,100 40 703.0 4C.0 230.0 36.0 

3/5A2 5anolane 95.5 59.0 30.0 18,100 40 703 116.0 230.0 36.0 

3/6 Sayun 65.0 28.0 27.0 6,200 41 362.5 28.0 240.0 23.0 

3/8 Sooksunt 62.0 22.5 28.0 10.600 47 270.0 71.0 160.0 18.0 

3/8C2 Sooksunt 62.0 22.5 28.0 10,600 30 210.0 71.0 160.0 18.0 

Stnv- numbers which followed by latter codes such as A, AI,82, and C2 indicate that modificatiors have been made to the 

oriqinal models to observe the performance responses.

Table 5.6 

Average testing results of commercial charcoal stoves 

Stove No. of Fuel used Burning rate 

no. test (gm) (gm/min) 

1/2 6 337.0 6.57 

1/3 6 332.0 6.17 

1/4 6 340.0 7.01 

1/5 18 330.0 6.47 

1/6 3 316.0 5.45 

1/7 6 316.0 5.45 

1/8 3 323.0 5.65 

1/9 3 313.0 5.9i 

1/10 3 295.0(min) 4.81(min) 

1/11 3 312.0 5.96 

1/12 7 316.0 6.01 

1/13 11 325.0 6.05 

1/14 6 327.0 5.73 

1/15 9 323.0 5.92 

1/16 6 301.0 5.29 

1/17 6 320.0 6.42 

1/18 7 325.0 6.17 

1/19 8 344.0 6.45 

1/20 6 315.0 5.10 

1/21 3 313.0 5.47 

1/22 3 317.0 5.96 

1/23 6 322.0 6.27 

1/24 6 327.0 6.23 

1/26 3 325.0 6.07 

1/28 9 342.0 6.82 

1/29 4 343.0 6.86 

88 

Time to boil 

(min) 

21.7 

22.3 

18.8 

21.1 

18.0 

28.0 

27.3 

23.0 

31.7 

22.3 

22.6 

23.9 

27.2 

24.6 

27.2 

20.0 

23.6 

23.8 

32.0(max) 

27.3 

23.3 

21.5 

22.7 

23.7 

20.1 

20.0 

Heat conversion 

efficiency(%) 

24.96 

25.70 

28.19 

30.53 

28.53 

25.61 

24.07 

28.42 

26.54 

26.41 

29.02 

26.12 

23.53(min) 

27.21 

27.45 

32.30 

26.85 

23.89 

24.94 

24.73 

28.11 

29.17 

25.60 

24.36 

25.60 

25.85

Table 5.6 

(continued) 

Stove No. of Fuel used Burning rate Time to boil Heat conversion 

no. test (gm) (gm/min) (min) efficiency(%) 

1/30 7 3 6 4.0(max) 7.77(max) 16.9 24.25 

1/31 6 334.0 7.17 16.7(min) 32.43(max) 

1/32 8 360.0 7.57 17.6 24.61 

1/33 3 340.0 7.04 18.3 30.51 

1/34 5 336.0 6.58 21.2 26.07 

1/35 6 340.0 6.83 19.8 27.35 

1/36 5 322.0 6.34 20.8 30.67 

1/37 3 322.0 5.75 26.0 28.07 

Average 327.0 6.21 22.8 27.00 

89

90 / 

so 

U 

70 

Figure 5.0 Time-Temperature characteristic curves of charcoal bucket stoves 

31175 AiN 14 20 

/ ' 

.20 

.*" 

4 "Good stove Poor stove 

(60 Stove No. 31 17 .5 AN 19 14 20 

' HU % 32.4 32.3 30.5 34.4 

$4s-o 

a)4) 

40 

30 

20 

10' 

0 

/ /' " 

" 

Time to boil (min.) 17 18 19 20 24 26 29 

Boiling duration (min.) 30 30 30 30 9 10 11 

Last temperature (C) 97 96 96 97 88 87 89 

Total operation time (min.) 47 48 49 50 54 56 59 

10 20 30 40 50 60 

Time of operation, min. 

14

dP 

33 

32 

31 

30 

29 

28 

27 

26 

25 

24 

23 

22 

21 

20 

19 

Figure 5.1 

Performance rating based on heat utilization 

efficiency (lU) of cormnercial charcoal bucket stoves. 

1 

STOVE NUMBER

34 

33 

32 

31 

30 

29 

28 

27 

28 

25 

24 

r,23 

H22 

.0 

0 

4 J 2 1 

Is 

17 

17 

16 

14 

13 

12 

11 

L 

Figure 5.2 

N 

Performance rating based on time to boil of 

commercial charcoal bucket stoves. 

M H M '1 1-1 r-1 4.-H M J N N C1 N'J 'M H4 

92 

STOVE NUMBER

Wood Stove without Chimney 

25 wood stoves were subjected to the performance tests. The results 

show that the efficiency of non-bucket wood stoves i.e., stove No. 2/1 to 

2 /24,varies from 14% - 23%. For bucket-type wood stove, (stove No. 1/2 to 

1/25), the efficiency varies from 18 - 25%. (See Fig. 5.3 - 5.4 and Table 

5.7). The time to boil for both types of stoves ranges from 17 - 19 min. 

and fuel burning rates range from 22 - 35 gm/min. The wood stoves with 

buckets have much the same level of effective performance as these nonbucket 

counterparts (that is around 21%). 

Wood Stove with Chimney 

Table 5.8 and Fig. 5.3 and 5.4 show that the efficiency of stove No. 

2/11, 2/12 and 2/15 is 13.88, 16.30 and 11.0, respectively. T,.z time to 

boil is in the range of 17 - 19 minutes. 

These chimneyed stoves perform at a considerably low level when 

compared to the wood stove without chimney. Hence, the wood stove with 

chimney can be regarded as an inefficient type of cooking stove. The low 

HU and long time to boil of commercial chimneyed wood stoves as compared 

with the nonchimneyed are mainly caused by two factors; 

a) Too much heat (and flame) loss has occurred through the flue gas 

exit hole which is located just the opposite of the fire feeding 

port and no flame restriction or baffle exists. 

b) The stoves are poorly designed in such a way that only a small 

portion of the pot bottom comes into contact with the flame, 

thus causing poor heat transfer. 

Rice Husk Stove with Chimney 

From Table 5.9, the performance of the six original models tested were 

as follows. The heat utilization efficiency ranged from 4.2 to 7.1% and 

averaged 5.6%. Time to boil was between 18.5 - 28.2 minutes and averaged 

23.4 minutes. The burning rate ranged from 58.5 - 160.7 gm/min and 

averaged 99.8. The overall rice husk consumption per test was on the 

average 5.2 kg. 

After the original designs were modified according to the specifications 

in Table 5.5, their performance improved considerably. The average HU 

increased to 8.3%. Time to boil varied greatly (15.7 - 30 min), but on the 

average remained like the unmodified model. The big reduction was in the 

fuel used and the average burning rate which were 4.0 kg and 79 gm/mmn 

respectively. This is equivalent to approximately a 25% fuel saving. The 

very low efficiency value of the original models is due mainly to a great 

amount of heat loss through the flue gas exit. For example, for stoves 3/4 

and 3/4A1, the efficiency of the former is increased by 100% (from 5.15 to 

10.30%) upon reducing the area of the flue gas outlet by one half (from 

93

dP 

Z 

27 

26 

25 Ficure 5.3 

24 

23 

22 

21 

20 

19 

18 

17 

16 

15 

14 

13 

12 

Performance rating based on heat utilization efficiency 

(HU) of nonchimneyed and chimneyed*wood stoves. 

STOVE NUMBER

o 

0 

0 

E-4 

2. 

21- 

26 

19- 

15 

13 

12 

.1 

10" 

RI 

W 

7, 

7- 

4" 

1-- 

Figure 5.4 Performance rating based on time to boil 

of nonchimneyed and chimneyed*wood stoves. 

(N ('TC I1(N(4HHN Cq ( ' .4 (N H H H. C WH 

HCJ H CJ' N HN'(N C N HH (N H CN 1- N 

H ~ ~ H H' ~ N ~ ~ 

95 

STOVE NUMBER

Table 5.7 

Average testing results of wood stoves without chimney 



2/1 6 1483 35.36(max) 12.0 17.59 

2/2 3 1308 31.08 14.0 19.25 

2/3 4 1251 28.60 13.7 19.08 

2/4 3 1134 25.80 14.0 20.96 

2/5 4 1078 23.07 17.0 23.57 

2/6 4 1394 30.23 16.2 14.20(min) 

2/7 3 1372 28.13 18.7(max) 15.39 

2/8 4 1236 27.46 15.0 20.92 

2/9 4 1266 27.84 15.5 19.48 

2/10 3 1303 28.74 15.3 16.77 

2/13 3 1192 25.29 17.0 20.20 

2/16 3 1468 31.50 16.7 14.37 

2/22 6 1258 29.31 13.0 23.80 

2/23 6 1143 25.82 14.5 23.20 

2/24 5 1034 22.57(min) 16.0 23.47 

1/2 3 1337 31.09 13.0 20.80 

i/8 3 1253 26.48 17.3 18.30 

1/9 3 1625 34.24 17.3 14.48 

1/12 3 1265 28.77 14.0 21.01 

1/13 3 1202 27.34 14.0 20.99 

1/19 3 1330 30.00 14.3 17.75 

1/20 3 1415 32.19 14.0 20.60 

1/21 3 1367 29.75 16.0 21.63 

1/24 8 1059 24.40 13.5 25.90 

1/25 10 1054 25.28 ll.8(min) 25.90(max) 

Average 1273 28.41 14.3 19.8. 

96

Table 5.8 

Average testing results of wood stoves with chimney 



2/11 3 1316 27.0 18.7 16.32 

2/12 3 1247 26.2 17.70 16.30 

2/15 3 2186 46.5 16.7 11.0 

Average 1583 33.2 17.7 14.54 

97

Table 5.9 

Average testing results of rice husk stoves with chimney 


no., test (gm) (gm/min) (min) efficiency(%) 

3/2 5 5863 117.30 20.0 5.48 

3/3 4 5147 93.30 25.2 4.95 

3/4 4 5303 103.59 21.3 5.15 

3/5 4 7789 160.70(max) 18.5 4.24(min) 

3/6 3 3736 65.56 27.0 7.13 

3/8 5 3394 58.49 28.2(nax) 6.57 

Original model ave. 5205 99.82 23.4 5.59 

3/4 Al 3 4472 84.45 23.0 10.30 

3/4 A3 3 3513 68.07 21.7 7.48 

3/4 BI 3 3877 70.57 25.0 7.23 

3/4 B2 3 2531 42.23 30.0 9.16 

3/5 A 4 6686 139.10 18.0 5.15 

3/5 Al 3 4280 93.74 15.7(min) 7.05 

3/5 A2 3 4436 88.12 20.3 11.14(max) 

3/8 C2 3 2498 4 8.46(min) 21.7 9.23 

Modified models ave. 4037 79.34 21.9 8.34 

* The test condition deviates from normal, using pot 30 cm. diameter. 

98

95 to 47 cm 2 ). The same result was also obtained from stove Number 3/5 and 

3/5Al where the efficiency was increased by 66% with the reduction of the 

original flue -as exit by approximately 60%. The chimney height also has 

an impact on the stove efficiency since too high a chimney causes high 

suction of hot gas; too low a chimney hinders the outflow of the gas and 

creates a difficulty in initial ignition. In both cases poor heat 

utilization efficiency will result. Stove No. 3/5 and 3/5A illustrate this 

effect. 

These trial modifications were later used as the bases for redesigning 

the improved model. 

Block diagrams in Fig. 5.5 and 5.6 show the HU and time to boil of the 

rice husk stove plotted against the stove number. 

Rice Husk Stove without Chimney 

Test results from Table 5.10 have indicated that the stove made 

according to the original drawing (that is, stove code A but with better 

steel material for construction) had the HU of 17% and time to boil of 

approximately 14 minutes. Various trials of modifications of physical 

structures shown in Table 5.4 (stove code B to I) took place such as the 

insulation of outer cone, changing of cone slope, changing size and number 

of air inlet holes, the inner cylinder height and exhausted gas outlet, and 

rice husk flow gap between the outer cone and inner cylinder. These 

parameters have, more or less, some influence on the stove performance. The 

reduction of exhausted area seems to increase the stove efficiency, as 

indicated by stoves B and D in Table 5.4. Stoves B and C illustrate the 

effect of the height of the outer cone: the HU increases from 15.34 to 

18.58% when the height decreases from 37.0 to 30.5 cm. However, the best 

combination was obtained from stove G where the HU and TTB are 20.3% and 

11.4 minutes respectively. This stove was used as a basis for the improved 

model. 

The foregoing sections summarize the stove testing results. A thorough 

analysis of the results of stove testing needs a knowledge of heat and mass 

transfers. To illustrate such a method of analysis, the results of testing 

the charcoal bucket stove and the wood stove without chimney will be discussed 

in detail in the following section. 

D. THE EFFECT OF INTERNAL AND EXTERNAL VARIABLES 

This section studies the effect of various factors on stove performance. 

The factors are divided into 2 main groups according to their characteristics: 

first, properties that are fixed for a stove such as the stove gap and inlet 

air area; secondly, properties that can be changed such as wind, humidity, 

and charcoal weight. The first group is called internal variables, and 

the second the external variables. 

99

Table 5.10 

Average testing results of rice husk stove without chimney 


no. test (gm) (gm/min) (min) efficiency'(%) 

A* 6 1929 44.04 13.8 16.97 

B 2 2002 47.12 12.5 15.34 

C 4 1628 38.73 12.0 18.58 

D 5 1804 42.75 12.2 18.32 

E 3 1848 42.69 13.3 16.00 

F 5 1736 41.24 12.2 19.52 

G 5 1887 45.57 11.4 20.29 

H 5 1704 40.36 12.2 17.68 

1 5 1755 42.39 11.4 18.87 

Average 1810 42.77 12.3 21.70 

* The model A is an original design. 

100

22 

21 

20 

19 

LB 

17 

16 

15 

14 

13 

12 

11 

10 

8 

7 

5. 

4 

3 

2 

4 -I 

Figure 5.5 Performance rating based on heat utilization 

0-och'Je ec- 

efficiency (HU) of nonchimneyed and chimneyed 

rice husk stoves. 

JA Ie cI 

cl i:xi & 

101 

STOVE NUMBER

0 

0 

* 

34 

32 

30 

28 

28 

24 

22 

20. 

18- 

L4. 

12 

10 

4-. 

4 - 

Figure 5.6 Performance rating based on time to 

boil of nonchimneyed and chimneyed rice 

husk stoves. 

nncn aye i -- -c c l Ie 

102 

STOVE NUMBER

Internal Variables 

The internal variables are the characteristics that come with the stove. 

They include all the geometrical structure of the stove., .rtove exhaust gap, 

grate-hole area, grate-to-pot distance, combustion chamber size, air inlet 

door, and grate thickness. The results of changing such variables will be 

discussed. For all terms used In the following section please refer to the 

illustration in Fig 7.1 in Chapr;er 7. 

Exhausted gap/exihausted area 

Test condition: Charcoal 400 gm. 

water 3,700 gm. 

pot diameter = 24 gm. 

Table 5.11 Test results of the effect of stove gap/exhausted area on HU and 

time to boil. 

Stove No. of Gap area Gap height Time to boil Unburned HU 

No. tests (sq cm) (cm) (min) charcoal (%) 

(sm) 

1/5 3 20.5 0.5 19.0 92 34.5 

4 65.6 1.6 18.0 70 29.7 

3 86.1 2.1 18.7 62 28.0 

4 98.4 2.4 18.0 54 27.2 

1/31 3 40.2 1.1 16.0 60 32.8 

3 65.6 1.6 16.3 60 29.3 

3 86.0 2.2 16.0 52 28.3 

3 98.6 2.6 18.0 48 26.6 

Results and Discussion 

From Table 5.11, as the exhausted gap increases from 0.5 cm to 2.4 cm 

for stove No. 1/5, and from 1.1 cm to 2.6 cm for stove No. 1/31, the HU 

value decreases from 34.5 to 27.2% and 32.8 to 26.6%, respectively. With 

stove No. 1/5, when the exhausted gap is increased by a factor of 4.8, the 

stove efficiency is decreased by the ratio of 21% of the original value. 

Similarly, an increase of the gap by a factor of 2.3 in stove No. 1/31 

decreased the stove efficiency by the ratio of 19%. Hence, both stoves 

show an identical trend. 

103

The efficiency of the stoves is inversely proportional to the exhausted 

gap or the exhausted area. The larger the exhaust area, the greater a 

combustion heat energy that is allowed to escape through it. The optimum 

gap determined from this experiment is 0.5 cm. From Fig. 5.7, if both lines 

are extrapolated, the efficiency of the stoves should be even higher, or 

approaching infinity as the gap area approaches zero. However, with the 

real physical structure of the stove, the exhausted gap of under 0.5 cm is 

considered the minimum limit for combustion air to flow through, without 

disturbing the optimum combustion rate, particularly when oper:ating the 

stove from cold conditions. 

Grate hoZe area 

Test condition: charcoal = 400 gm. 

water = 3,700 gm. 

pot diameter = 24 cm. 

Table 5.12 Test results of the effect of grate hole area on HU and time to 

boil. 

Stove 

No. 

No. of 

tests 

Gap height 

(cm) % 

Grate hole 

(cm 2 ) 

area 

(%)* 

Time to boil 

(min) 

Unburned 

charcoal 

(gm) 

1/5 3 0.5 80.0 45.3 19 S2 34.5 

3 52.8 29.9 21 S8 34.1 

5 26.4 14.9 26 109 32.3 

1/5 4 2.5 80.0 45.3 18 54 27.3 

3 52.8 29.9 20 67 27.1 

3 

* -% of total grate area 

26.4 14.9 24 87 27.0 


From Table 5.12, and Fig. 5.8 the efficiency of the stove increases with 

the increase in grate hole area. With a smaller gap of 0.5 cm, the effect 

is, however, more prominent than with the larger gap of 2.5 cm. This should 

be expected since the gap has proven to be a strong factor controlling the 

stove efficiency as previously discussed. 

Grate hole area has a strong influence on time to boil and the amount 

of unburned charcoal. At 0.5 cm gap, time to boil increases from 19 to 

26 minutes and the amount of unburned charcoal increases from 92 to 109 gm 

as its grate hole area decreases from 80 to 26.4 sq cm. Similarly, at 

2.5 cm gap, the decrease in the grate hole area by the same amount causes 

time to boil and the amount of unburned charcoal to increase from 18 to 24 

minutes and 54 to 87 gm, respectively. 

104 

HU 

(%)

36 

34 -. 319 

13 

1/5 

.TTB 

32 - 1/31 18 

II .0 

30 0. 31 

00 

28 - 

-A16 

)(1/5 

3HU 

01/3 1 

261 

15 

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

gap, cm. 

Fig. 5.7 The effect of e,:hausted gap on the stove efficiency and 

time to boil. 

105 

20 

0

36 128 

34- 0 HU 26 

32 1.,0\'. 3gap.5 cm. 24o 24 

\ 0 

30 N I 22P 

28-. 220 

28 gap 2.5 cm. -TTB 20 

Y" '" AHU 

26 I I I N - . TTB 18 

10 20 30 40 50 60 70 80 90 

Grate hole area, cm. 

Fig. 5.8 The effect of the grate hole area on che stove efficiency 

and time to boil. 

106


Test condition: charcoal = 4O gm. 

water = - 3,700 gm. 


Table 5.13 Test result of the effect of grate-to-pot distance on HU and time 

to boil. 

Stove No. No. of test Grate-to-pot distance Time to boil HU 

(cm) (min) (%) 

1/4 6 11.0 18.8 28.2 


5 9.3 15.4 31.1 

6 7.5 19.0 28.2 

The curve as shown in Fig. 5.9 indicates that the optimum value of 

grate-to-pot distance is 9.3 cm. At this point the stove yields 31% 

efficiency. 

The grate distance is one o± the important factors that distinctly 

influence the stove performance. A parabolic curve means that either too 

short or too long a grate-to-pot distance will lower the stove efficiency. 

With the shallow grate, the hot charcoal bed is closer to the gap and more 

heat will be lost through it by radiation. In addition, the shallow grate 

will decrease the firing chamber capacity, causing a packing up of charcoal 

up to the pot bottom. Consequently, the draft from the bottom is limited 

and poor combustion results. On the other hand, if the grate is too far 

from the pot, the stove efficiency will fall again. This can be explained 

in terms of radiative heat flux from surface 1 to surface 2 which is 

inversely proportional to the distance. Hence, when the grate-to-pot 

distance is past the optimum value the efficiency begins to fall. From this 

experiment witl- the medium stove size (23.5 cm pot hole diameter) and 

400 gm of charcoal load, the cptimum value of grate-to-pot distance is about 

9 cm. 

Combustion chmber size 

Test condition: charcoal 400 gm. 



107

Table 5.14 Test result of the effect of combustion chamber size on HU and 

time to boil. 

Stove No. No. of test Combustion chamber volume Time to boil. HU 

(cu cm) (min) (%) 

1/28 9 4,216 20.1 25.6 

4 3,414 20.0 25.9 

l/A3 4 2,'.0 15.7 30.8 

3 1,787 18.0 33.1 

I/D1 4 2,946 19.7 26.9 


4 1,510 18.0 30.6 

It can be seen from Table 5.14 and Fig. 5.10 that the decrease in 

combustion chamber increases the HU value of the stove. For example, the 

HU value of stove No. 1/A3 increases from 30.8 to 33.1% when the combustion 

chamber decreases from 2,460 to 1,787 cu cm; the HU value of stove No. l/Dl 

also increases from 26.9 to 30.6% corresponding to the decrease in the 

chamber from 2,946 to 1,510 cu cm. Not much increase in the HU value of 

stove No. 1/28 is observed as the result of the reduction of the chamber 

because the percentage of reduction from original design is smallest. 

Besides, this stove has many features in addition to the chamber size that 

are poorly designed (see Annex I). 

The volume of the combustion chamber is reduced by adding a clay-rice 

husk ash mixture to the inside wall of the stove. By doing so, the wall 

thickness increases; consequently, the insulation may improve slightly. But 

more importantly, the diameter of the combustion chamber decreases due to 

the enlargement of the stove wall. With the same amount of charcoal being 

loaded, the distance between the glowing charcoal and the pot bottom gets 

nearer as compared with the stove without reducing the combustion chamber. 

As a consequence, more radiative heat can reach the water as the distance 

becomes smaller. 

For stove No. 1/28, the reduction of the chamber does not show a 

significant effect on the performance. This is due to the fact that although 

its volume is reduced from 4,216 to 3,414 cu cm, the chamber size is still 

quite large to contain 400 gm of charcoal. The distance between the glowing 

charcoal and the pot bottom would therefore vary slightly when the same 

amount of charcoal is loaded. The improvement of the radiative heac transfer 

is, hence, insufficient to clearly reflect its effect on the stove 

performance. However, a slight increase of the HU value can be noticed 

from the experiment. 

108

32 

31 

30 

29 

28- 

27 5 

Fig. 5.9 

/ 

/ 

/ 

/. 

/18 

" 

TTB 

1 

6 7 8 9 10 11 12 

Grate-to-pot distance, cm. 

The effect of grate-to-pot distance on the stove efficiency 

and time to boil 

109 

HU 

20 

19 . 

17 

16 

15 

13 

0 

.o 

0

Ai, inZet door 




Table 5.15 Test result of the effect of air inlet door on HU and time to boil. 

Stove No. No. of tests Exhausted gap Air Inlet opening Time to boil HU 

(cm) (%) (sq cm) (min) (%) 

1/5 18 1 100 66.0 21.0 30.5 


8 75 49.5 24.9 29.6 

7 50 33.0 22.1 29.8 

7 25 16.5 22.6 30.9 

The effect of air inlet door area is small. The air inlet varies from 

100% opening down to 25%, the HU value only differs by 1.3%. See Fig. 5.11. 

Since the amount of air flow through the stove combustion chamber is 

governed by the temperature gradient Detween the air inlet door and the 

exhausted gap, if the inlet opening gets smaller, by the equation of 

continuity, i.e., Qair = AVi - A2V2 = constant, the velocity of the 

inlet air will be increased. Hence, the combustion rate will not be affected 

by the supply of oxygen in the air. This is why the HU value of Fig. 5.11 

is constant. The time to boil, however, shows the tendency of increasing 

as the air inlet area is decreased. 

Grate thickness 


water = 3,700 gm. 


110

# 1/28 

34 20 

32 - HU 19 

/./"A -.- TTB 

30 A18 . 

g 0 

28 /1 

/ 

26 / o-"2/28 16 

24 

1000 1500 

I 

2000 

I 

2500 

I 

3000 

I 

3500 4000 4500 

15 

5000 

3 

Combustion chamber volume, cm 

Fig. 5.10 The effect of combustion chamber volume on the stove efficiency 

and time to boil of three different stoves tested. 

111

50 25 

45- 

HU 24 

45--. HUH TTB 2 

0 

40 23 -0 

....... .......... -=W 

AA 

35 0 0 HU 22 H 

30 TTB 21 

25 I 20 

20 30 40 50 60 79 80 90 100 110 

Air inlet door opening, % 

Fig. 5.11 The effect of air inlet door on the stove efficiency 


112

Table 5.16 Test result of the effect of grate thickness on stove performance 

Stove No. No. of test Grate thickness Time to boil HU 

(cm) (min) (%) 

1/E3 5 2.0 16.6 31.3 

5 3.6 16.0 34.1 

1/E4 5 2.0 19.4 30.1 


5 3.6 16.8 33.6 

Only two values of grate thickness, as restricted by the stove firing 

chamber and grate-to-pot distance parameters, were chose- for the experiment: 

2 cm and 3.6 cm. The tests for efficiency were perform, in stove No. l/E3 

and l/E4. The test results from Table 5.16 and Fig. 5.12 showed that the 

thicker grate gives a higher efficiency. The HU values for the first stove 

are 31.3 and 34.1% for the grate of 2.0 and 3.6 cm thick, and 30.1 and 33.6% 

for the second stove, respectively. 

With the thicker grate, the heat lost by conduction is smaller because 

the grate is made of clay and rice husk ash which is a considerably good 

insulator. Thereforet, the thicker grame seems to be the best (as long as 

the thickness incre e has not significantly altered other physical para 

meters). Time to boil seems to slightly increase as the result of this 

change. However, more experiments should be performed to determine the 

optimum value of grate thickness based on different size of stoves. 

Stove insulation 




Table 5.17 Test result of the effect of insulation on HU and time to boil. 

Pair No. Stove No. Insulation Time to boil HU 

(min) (%) 

1 1/3 no 22.3 25.7 

1/4 yes 18.8 28.2 

2 1/23 no 21.5 29.2 

1/5 yes 21.1 30.5 

3 1/33 no 18.3 30.5 

1/31 yes 16.7 32.4 

113

35 20 

A l/E3 - HU 

34 -.- TTB 19 

l/E4 

33 ' 18 

32 17 

1/E4 

31 - 0 1/E3 16 

/ /E 

30 1 

0 1 

 

3 4 

1 

5 6 7 

- 15 

8 

Grate thickness, cm 

Fig. 5.12 The effect of grate thickness on the stove efficiency 

and time to boil 

114 

0 

0


The bucket stove as the name implies has a bucket to contain the pottery 

body inside; between the bucket and the body is found insulation normally 

made from rice husk ash-clay light weight material. The function of the 

insulation and the bucket are threefold: that is, to minimize heat loss from 

the inside wall; to provide the constraint against thermal expansion without 

causing stove cracking or the stove integrity in long term service; and to 

facilitate transportability of users both frow the market and during use. 

To study the effect of insulation, a matched pair of identical stoves were 

tested (one with,the other without insulation and bucket); the results are 

as shown in Table 5.17. From Table 5.1 it is quite apparent that the 

non-insulated stove performs more poorly than the insulated counterparts. 

The pair of larger size stoves (No. 1/3 and 1/4) showed a stronger effect 

than the smaller size pair in both HU% and time to boil. This may be due 

to the fact that a larger size stove has greater surface area for heat loss 

than the smaller one. 

Stove's weight 


water = 3,700 gm 

pot diameter 24 cm. 

Table 5.18 Test result of the effect of stove weight on the HU and time to 

boil. 

Pair No. Stove No. Stove weight Time to boil HU 

(kg) (min) (%) 

1 1/2 12.2 21.7 25.0 

1/5 9.3 21.1 30.5 

2 1/30 18.0 16.9 24.3 

1/31 11.8 16.7 32.4 

3 1/32 8.2 17.6 24.6 

1/33 6.7 18.3 30.5 

4 1/35 8.0 19o8 27.2 


1/36 6.5 20.8 30.7 

Heat absorption by the stove largely depends on its weight. This is 

particularly true for the household cooking stove where it is normally started 

from cold conditions and used for a short duration (within one hour) with 

115

limited charcoal load. Almost all of the stoves tested regardless of this 

variation in physical parameters show that the charcoal stove efficiency 

varies more or less inversely with its weipht. The stove sample pairs in 

Table 5.18 come from the same make and debign. 

From Table 5.18, it is quite clear that the stove weight has a strong 

effect on the stove heat utilization efficie-cy but almost no effect on the 

time to boil. It must be pointed out, however, that the chamber size of 

each stove in the pair studied was not the same. It was larger for the 

heavier stove. Therefore, combustion chamber size must also be combined 

with the stove weight. It is not possible to single out the weight factor 

alone. 

The Effect of External Variables 

The external variables are the environmental factors. These include 

the initial weight of charcoal and water, pot size, charcoal size, wind, 

and air relative humidity. 

Initial weight of charcoal 

Test condition: pot diameter = 24 cm. 

exhausted gap = 1 cm. 

water weight = 2,300, 3,000, 3,700 gm. 

Table 5.19 Test result of the effect of initial weight of charcoal on stove 

HU and time to boil. 

Stove No. No. of test Water weight Charcoal weight Time to boil HU 

(gm) (gm) (min) (%) 

1/5 5 2,300 300 17.0 26.3 

4 350 14.0 27.6 

4 450 13.0 30.8 

1/5 4 3,000 300 16.5 30.1 

4 350 16.5 30.8 

4 450 16.8 32.2 

1/5 4 3,700 300 24.0 30.7 

4 350 21.0 30.5 

4 450 19.0 32.0 

116


In this experiment, the weight of charcoal varied from 300 to 350 and 

450 gm, and the weight of water controlled at 3 levels: 2,300, 3,000, and 

3,700 gm. Test results from Taole 5.19 and Fig. 5.13 showed that at all 

water weight levels, the eff.ciency of the stove increases witi the increase 

in charcoal load. The trend is weaker, however, as Lhe amount of water I s 

increased to the highest !nevel (3,700 gi) Time to boil is also reduced as 

the charcoal load is increased. 

These behaviors should be n.:-: L,tcd because whC1 Lhe amount of charcoal 

increases, the distance between the top charcoal layer and the pot bottom 

decreases as previously discussed. 'urthermore, the increase in charcoal 

load has contributed to more energy input but with a lower percentage of 

heat loss due to the absorption by the the stove's mass. 

InitiaZ weight of water 

Test condition: pot diameter = 24 cm. 

charcoal weight = 300, 350, 450 gm. 

exhausted gap = 1 cm. 

Table 5.20 Test result of the effect of initial weight of water on HU and 

time to boil. 

Stove No. No. of tests Charcoal weight Water weight Time to boil HU 

(gm) (gm) (min) (%) 

1/5 4 300 2,300 17.0 26.3 

4 3,000 16.5 3001 

4 3,700 24.0 . .7 

1/5 4 350 2,300 14.0 27.6 

4 3,000 16.5 30.8 

4 3,700 21.0 30.5 

1/5 4 450 2,300 13.0 30.8 

4 3,000 16,8 32.2 

4 3,700 19.0 32.0 

117

36 

34 \"22 

34 

- 

\.. 

0 

A 

TIME TO BOIL 

WATER WIGHT 

2,300 Sm 

3,000 gm 

32 a 3,700 gm 0 

S30 2 

28-L6 

26 1 

0 

0 

- 24 

0 o 0 

16 

SIII I I I 

242001 

200 250 300 350 400 450 500 550 

Charcoal weight, gm 

Fig. 5.13 The effect of the initial weight of charcoal on the stove 

efficiency and time to boil 

118 

600 

L4 

1


The effect of initial water weight variation on the HU and time to boil 

was tested at three charcoal load levels. Test results from Table 5.20 shows 

that, in most cases, the efficiency increases slightly with the increase of 

initial water weight. The effect is considerably noticeable only when the 

water weight is increased from 2,300 gm to 3,000 gm, but after that point 

the efficiency seems to reach the peak regardless of chaxcoal load. The 

increased in time to boil is evident as the amount of water is increased. 

Theoretically, the amount of heat required to increase the temperature 

up to its boiling point is proportional to the amount of water. Therefore, 

it is no surprise that time to boil increases from 17.0 to 24.0 minutes in 

the 300 gm charcoal loadfrom 14.3 to 21.0 minutes in the 350 gm charcoal, 

and from 13.0 to 19.0 minutes in the 450 gm charcoal load as the weight of 

water increases from 2,300 to 3,700 kg. As for the HU, since the geometrical 

structure of the stove has not changed, heat produced by combustion of 

charcoal occurs at the same rate. Therefore, the rate of heat transfer to 

the water is not varied by the amount of water. Consequently, the 

accumulation of energy by the water is unchanged. Even after the temperature 

of water reaches the boiling point, heat accepted by the water within half 

an hour of prolonged boiling is not different for all cases. The 

efficiency of the stove, therefore, is not greatly effected by the change 

of the initial weight of water particularly when the charcoal load satisfies 

the combustion chamber capacity as in the case of 350 and 450 gm. 

Pot size 

Test condition: charcoal weight = 400 gm. 

water weight 3,700 gm. 

Table 5,21 Test result of the effect of pot size on HU and time to boil, 

Stove No. No. of tests Pot size Time to boil HU 

(cm) (min) (%) 

1/4 6 24 18.8 28.2 

5 28 16.4 28.5 

5 32 16.4 28.1 

1/E3 5 24 16.5 34.1 

3 28 15.0 34.1 

3 32 16.0 34.8 

119


The size of the cooking containers does not affect the efficiency of 

the stove. As shown in Table 5.21, the HU values are nearly constant when 

the size of the pot varies without changing the amount of water. This is 

due to the fact that in changing the pot size, the geometrical structure 

has not changed significantly: the distance between the top glowing 

charcoal layer to the pot bottow will change only slightly;i.e., a larger 

pot sits higher on the stoVe'S pot rests but at the same time a larger pot has 

more heat absorbing surface at the bottom and side wall. However, one might 

expect more heat loss in the larger pot than in the smaller one, owing to a 

larger surface exposed to the surroundings but this may be offset by the 

greater water evaporating surface for the larger pot size, The effect of pot 

size on time to boil seems to be insignificant within the size range tested. 

Charcoal size 

Test condition: charcoal weight 400 gm. 

water weight = 3,700 gm. 


Table 5.22 Test result of the effect of charcoal size on HU and time to boil, 

Stove No. No. of tests Charcoal size Time to boil HU 

(cm) (mill) (%) 

1/5 3 2.54 18.3 31.5 

3 10.16 18.3 31.6 

1/12 3 2,54 17.7 27.5 

3 10.16 22.3 28.0 

1/14 3 2.54 17.0 24.4 

3 10.16 23.7 23.8 

1/20 3 2.54 19.0 24.5 


3 1016 23.7 25.5 

Table 5.22 indicates that the size of the charcoal has an insignificant 

effect on the stove efficiency. Time to boil increases as the size of the 

charcoal increases: 17.7 to 22.3 minutes in stove No. 1/12, 17.0 to 23.7 

minutes in stove No. 1/1'#, and 19.0 to 23.7 minutes in stove No. 1/20. For 

stove No. 1/5, the time to boil does not change. This observation can be 

perhaps explained by the fact that the design of this stove, particularly 

120

the grate, is superior to others and therfore can zompensate for charcoal 

size while the average design can not. 

The increase in time to boil could be attributed to the decrease in 

burning surface of the larger size pieces charcoal. During the heating up 

time, heat is released from the combustion faster when the charcoal size is 

small, and vice versa. Therefore, the water needs a shorter time to boil 

with the small-size charcoal. However, a larger amount of charcoal is used 

up during the heating-up process. When the experiment is in the boiling 

period, the rate of heat released from the small-size charcoal diminishus 

because a large portion of the charcoal was ised previously. The overall 

effect is that the efficiency is not significantly different between the 

two charcoal sizes investigated. 

Wind 




Table 5.23 Test result of the effect of wind on HU and time to boil 

Stove No. No. of tests Wind spped Time to boil HU 

m/min min rel. change % % rel. change % 

41 8 0 21.1 30.5 

1/5 1 3 80 18.0 -14.7 22.6 -26 

80 7 0 22.6 18.4 

1/12 2 3 80 23.3 + 5.7 18.4 -36 

1/17 50 6 0 20.0 32.3 

1.2 3 80 26 +30.0 21.9 -32 

113 6 0 27.2 23.5 

1/14 2.5 3 80 not boil + 15.6 -34 

1/20 102 6 0 30.3 24.9 

2 3 80 not boil + 16.6 -33 


The effect of wind was simulated by the use of an electric fan 

approximately 16 inches in diameter placed at the distance of about 2 m from 

the stove air inlet port. The wind speed was measured by a vane type 

anemometer located right in front of the air inlet port. The result from 

121

Table 5.23 shows that the stove efficiency drops drastically when subjected 

to the wind of 80 m/mn (or 4.8 km/hr). The drop in HU relative to original 

value (without the wind) ranges from 26 - 36%. Time to boil,except for stove 

number 1/5, increased as little as 6% of original value to 30% and even to 

infinity in the case of stove number 1/14 and 1/20 where the water cannot be 

brought to the boil. It is interesting to note that stove number 1/5 has 

less time to boil when subjected to wind and the least change in HU. The 

behivior of this stove can be simply explained by the better control of heat 

loss since its exhausted gap/area (1 cm/41 cm 2 ) is very narrow (Table 5.1). 

For those stoves with wider gaps and exhausted areas such as number 1/14 and 

1/20 (where the exhausted gaps/areas are 2.5 cm/113 cm 2 , and 2.0 cm/102 cm 2 , 

respectively), the HU drops and time to boil increases considerably. 

Air relative humidity 




Table 5.24 Test result of the effect of air relative humidity on HU and time 

to boil. 

Stove No. No. of tests Humidity Time to boil HU 

(%) (min) (%) 

1/5 1 68 23.0 29.0 


2 74 20.5 31.6 

1 76 21.0 31.6 

1 78 22.0 31.3 

1 80 19.0 30.6 

3 92 22.7 29.2 

The effect of air relative humidity on the HU and time to boil was 

investigated using tha test results that were previously recorded over a 

long period of time in which changes in humidity had actually occurred. The 

test results in Table 5.24 indicate that the HU and time to boil do not vary 

with the humidity. 

Air relative humidity presumably should influence the rate of water 

evaporation from the pot during boiling. For example, at low relative 

humidity the evaporation rate should be higher and vice versa. However, 

this has proved not to be the case. The plausible explanation is that at 

122

a very high vapor pressure of the boiling water, resulting from an inteluse 

heat generated by the glowing charcoal under the pot, more than enough energy 

potential is created to evaporate the weter from the pot. 

The change in air relative humidity, therefore, can have essentially no 

additionai effect on the evaporation rate. 

E. WOOD STOVE WITHOUT CHIMNEY 

In investigating the performance of the wood stove without chimney, the 

variables are also classified in a similar way as in the charcoal stove. 

They are divided into two groups--internal and external variables. 

Internal Variables 

In this section, the effect of internal variabaes are studied. These 

internal variables are stove gap, grate vs nongrate, grate hole area, and 

grate-to-pot distance. 

Stove gap/exhausted area 

Table 5.25 Test result of the effect of stove gap on HU and time to boil of 

the wood stove. 

Stove No. No. of tests Gap exhausted Time to boil HU 

(cm) (min) (%) 

2/25R 5 1 12.6 28.92 

2/88 4 1 11.2 27.62 

2/lB 5 1.5 12.4 27.34 

2/13E 5 1.3 12.0 27.04 

2/24R 8 0.63 13.5 25.93 

2/5B 3 1.5 12.7 25.71 

2/22B 8 1.5 14.0 24.43 

2/4B 3 2.7 11.0 23.47 

2/23 6 1.8 14.5 23.20 

2/9B 8 2.0 12.0 22.76 

2/21N 3 3.0 16.0 21.63 

2/12S 3 2.0 14.0 21.01 

2/13S 3 1.6 14.0 20.99 

2/2S 3 2.0 13.0 20.80 

2/20S 3 2.0 14.7 20.69 

2/18S 3 2.0 13.7 20.28 

2/24S 3 1.5 14.3 20.19 

2/8S 3 1.5 17.3 18.13 

2/19S 3 2.5 14.3 17.75 

2/9S 3 3.0 17.3 14.48 

123


As indicated with the charcoal stove, the gap has an effect on the stove 

efficiency. In the case of the wood stove, even when the mechanism of heat 

transfer is different, this effect is also observed. Fig. 5.14 is the 

plot of the HU values of wood stoves from various manufacturers against the 

gap heights. The scattering of points in the g~r is due to variations of 

stove geometry of different makes. Nevertheless, the trend can be deduced 

easily; as the gap height decreases, the stove efficiency increases. 

The increase of stove efficiency with the decrease of gap can be 

explained in the same line as that of the charcoal stove. When the gap is 

large, heat is easily lost through the gap by the flame and exhaust gas 

convections. With the smaller gap the flame from burning firewood has a 

better contact with the pot side wall before exit to the atmosphere. 

Grate vs nongrate dsiw> 

Table 5.26 Test result of the effect of grate on HU and time to boil of wood 

Stove. 

Stove No. of Base or grate-to- 

'a. tests pot-distance, cm 

2/5 4 14.0 

2/6 4 14.0 

2/7 3 14.0 

2/9 4 11.5 

2/10 3 12.0 

Average 13.1 

2/4 3 12.0 

2/13 3 14.5 

2/22 6 12.2 

2/23 6 12.2 

2/24 5 13.0 

Average 12.8 

Firewood 

used, gm 

1,078 

1,394 

1,372 

1,266 

1,303 

1,283 

1,134 

1,192 

1,258 

1,143 

1,034 

1,152 

124 

Time to boil 

min 

17 

16.2 

18.7 

15.5 

15.3 

16.5 

14 

17 

13 

14.5 

16 

14.9 

HU 

% 

23.6 

14.6 

15.4 

19.5 

16.8 

17.9 

21.0 

20.2 

23.8 

23.2 

23.5 

22.3 

Remarks 

stove 

group 

without 

grate 


group 

with 

grate

Fig. 5.14 The effect of exhausted gap on efficiency of various wood 

stoves. 

30 

20 

0 

0 

0 o0 

0 

20 

10 1 2 3 cm 

125 

0 

0 

0 

0 

Exhausted Gap


Comparing the two designs of wood stove (with and without grate), the 

test results in Table 5.26 indicate that with comparable base or grate-topot 

distance the stove group with grate has a much better heat utilization 

efficiency on the average.' The absolute efficiency difference is 4.4%. The 

times to boil are 16.5 and 14.4 minutes for the group without and with grates 

respectively. This difference, however, is considered to be insignificant 

for practical use. The stove with grate consumes approximately 10% less 

fuel on the average than the group without grate. 

The reason for the better performance of the stove with grate is that 

the primary air induced from underneath the grate contributes to a more 

complete combustion of fuel than those stoves without grates where the air 

can enter the combustion chamber through the firewood feeding port only. 

The poorer combustion of nongrate stoves can be easily observed by the end 

of the test since more unburned charcoal remains. 

Grate hoie area 

Table 5.27 Test result of the effect of grate hole area on wood stove 

performance. 

Stove 

No. 

No. of 

test number 

Grate hole 

diameter 

(cm) 

area 

(sq cm) 

Time to boil 

min average % 

2/8B 4 90 1.5 159.0 11.2 27.68 

2/23 6 90 1.5 159.0 14.5 23.20 

2/lB 5 90 1.5 159.0 12.4 27.34 

2/13E 5 90 1.5 159.0 12.0 27.04 

2/22B 8 90 1.5 159.0 14.0 24.43 

2/1GI 7 90 1.5 159.0 12.4 25.97 

2/24R 8 90 1.5 159.0 13.5 25.93 

HU 

average 

2/25B 4 90 1.5 159.0 11.7 17.7 25.27 25.5 

2/8E 9 37 2.5 181.6 16.7 25.57 

2 /20A 10 37 2.5 181.6 15.9 23.56 

2/13B 8 37 2.5 181.6 12.0 14.9 22.76 24.0 

2/8GI 4 61 1.23 72.5 12.0 26.36 

2/IA 6 61 1.23 72.5 13.8 12.9 25.12 25.7 

126


The effect of grate hole area on the stove efficiency was studied by 

selecting stoves of different grate designs. Three sets of hole diameter 

and a varying number of holes were investigated; they are: A, 2.5 cm 

diameter and 37 holes; B, 1.5 cm diameter and 90 holes; and C, 1.23 cm 

diameter and 61 holes. The respective grate hole areas of A, B, and C are 

181.6, 159.0, and 72.5 sq cm. The efficiencies of A, B, and C are shown 

in Table 5.27. Only a slight increase in the stove efficiency with the 

decrease in the total grate hole area was observed: the efficiency of A 

was 24.0%, B 25.5%, and C 25.74%. 

The above phenomenon can be explained in terms of radiative heat loss. 

Through the grate holes, radiative heat can easily pass to the ash chamber. 

Consequently, a grate with a smaller total hole area improves the performance 

of the stove. In addition, the secondary air is always available through 

the firewood feeding port; therefore, the reduction of primary air itilet 

area by almost 2/3 does not cause the stove performance to change significantly. 

&rate-to-pot distance 

Table 5.28 Test result of the effect of grate-to-pot distance on stove 


Stove No. of Grate distance Time to boil HU 

No. tests (cm) min average (%) average 

2/Al 3 9 15.0 23.04 

2/AlA 4 9 14.5 24.48 

2/AlAl 3 9 15.0 25.70 

2/A2A 4 9 14.25 26.00 

2/A2 3 9 14.67 14.7 24.32 24.7 

2/Cl 5 10 14.6 25.10 

2/CIA 4 10 14.75 27.12 

2/D2A 4 10 15.25 25.20 

2/D2 3 10 14.66 25.34 

2/E2 3 10 16.0 25.00 

2/Fl 6 10 15.33 26.05 

2/lG 3 10 15.66 15.2 25.65 25.6 

2/A2 5 11 15.6 27.53 

2/A3A 4 11 18.0 26.82 

2/A4A 3 11 18.0 28.0 

2/A4 5 11 18.0 17.4 28.25 27.7 

2/C2 5 12 15.2 23.78 

2/C2A 4 12 14.5 25.87 

2/DI 3 12 13.67 25.00 

2/DIA 4 12 13.75 26.82 

2/F2 6 12 14.5 26.35 

2/F2A 3 12 14.33 14.3 26.80 25.8 

2/30B 6 13 21 19.11 

2/30A 3 15 18.33 l'.75 

2/30 3 16 28.67 15.67 

127


The effect of the grate-to-pot distance on the stove performance is 

shown in Table 5.27 and Fig. 5.15. As the distance increases from 9 cm to 

about 11.0 cm, the average efficiency increases from 24.7 to 27.7%. However, 

as the distance increases further, tile stove efficiency drops. This 

behavior is also observed with the charcoal stove. 

At the small grate-to-pot distance, it is likely that the glowing wood 

is too near to the gap, causing high convective heat loss through the gap. 

Moreover, with too small a distance, fUrewood pieces would tend to jam up 

the combustion chamber causing limited flame to come into contact with the 

pot bottom and insufficient temperature of the chamber itself to initiate 

off-gas combustion with the incoming secondary air. When the distance 

increases, this loss reduces; the performance, hence, improves. However, 

at great distances the radiative heat which is intercepted by the pot drops 

more quickly than the decrease in heat loss through the gap, resulting in 

the poor performance of the stove. 

External Variables 

Only two external variables are studied: wind effect, and fuel feed 

rate. 

Wind effect 

Table 5.29 Test result of the effect of wind ol wood sto.'e performance. 

Stove No. No. of tests Wind velocity Time to boil HU 

(km/hr) (min) (%) 

2/2S 3 normal 13.0 17.65 

2/2B 3 6.3 13.7 16.21 

2/21N 3 normal 16.0 21.63 

2/21W 3 6.0 14.7 17.03 

2/25C 8 normal 11.9 21.64 

2/25D 3 5.0 14.0 14.58 


From Table 5.28, wind is found to have a strong effect on the efficiency 

of the wood stove, in one experiment, the HU values dropped from 21.63% to 

17.03%, when the wind is induced through the use of an electric fan. In 

another experiment, the IIUvalues decreased from 21.64 to 14.58%. All of 

128

Fig. 5.15 The effect of grate-to-pot distance on the heat utilization 

efficiency (HU) of wood stoves 

30 

0 

00 

20 0 

10tI I I I 

10 9 10 11 12 13 14 15 16 17 

00 

129 

0 

Grate-to-pot distance, cm

the experiments, including those with the charcoal bucket stove, indicate 

a similar effect when the stove is subjected to wind. The amount of drop 

in efficiency, however, depends on the design characteristics, particularly 

the exhausted gap and fuel feeding port size. 

The decline in performance is due to the increase of heat loss by 

flue gas and flame convection through the gap, and the oversupply of air to 

the combustion. If more air is supplied than required by the combusited 

woL., the heat-up of excess air will decrease the temperature of the 

combustion chamber. Therefore, the warm excess air, which contains a large 

amount of thermal energywill be lost with the flue gas. 

FueZ feed rate 

Table 5.30 Test result of the effect of firewood feeding rate on the stove 


Stove No. No. of Average feeding rate Time to boil HU Remarks 

tests gm/min min % 

2/8E 3 21.5 13.8 24.8 grate-to 

3 25.7 11.3 22.5 pot 

distance 

3 27.9 15.0 18.5 = 12 cm 

2/13A 3 31.6 11.4 23.5 for both 

tests 

3 38.8 9.7 21.9 


2 42.0 9.4 20.9 

Unlike the charcoal stove where the fuel is loaded in the combustion 

chamber at one time at the begining of ignition, the wood stove needs to be 

fed with firewood gradually and at a proper.distance to obtain the best 

combustion flame directed toward the pot bottom. The firewood feeding rate 

as shown in Table 5.29 indicates that this factor is quite sensitive to the 

efficiency of the stove. A higher feed rate causes the drop in HU for both 

stoves evaluated. The time to boil shows a decreasing trend as the feed rate 

is increased (with one exception, for stove number 2/8E, where at the fastest 

rate of 27.9 gm/min the time to boil increases). This may be due to the clogged 

up combustion chamber and firing since this stove has a small firewood feeding 

port and combustion chamber. 

130

The drop in HU with a faster firewood feeding rate can be recognized 

by two important phenomena; first, the rate of heat absoption by the pot 

is not directly proportional to the rate of heat released by the fuel, 

particu7iarly when the flame is forced through the exhausted gap with poor 

contact with the pot side; secondly, the clogging-up effect of the 

combustion chamber when too much or too fast firewood is fed in causes the 

incomplete combustion of hot gas. 

131

Chapter 6 

Theoretical Analysis of Charcoal Stove

THEORETICAL ANALYSIS OF THE CHARCOAL STOVE 

A. MATHEMATICAL MODEL OF THE BUCKET STOVES 

As seen in the preceding sections, the effects of only a few factors on 

stove efficiency were studied experimentally. These factors include the 

distance from grate to pot H, the grate hole area Ag, the gap height G, the 

wall thickness D, and the stove weight m s . Consequently to be of any use, 

any mathematical model of the stoves has to relate the efficiency to these 

factors. It is the purpose of this section to develop such a model. 

Prior to the development of the mathematical model, an understanding of 

the heat transfer mechanisms occuring in the stove is essential. These 

mechanisms are briefly described in this section. They are then related to 

the above factors. The model is subsequently developed; parameters in the 

model are evaluated by fitting the model to the experimental results shown 

in the previous sections. With the obtained values of the parameters, the 

model is used to predict the change of efficiency due to variation of one of 

the factors. 

Mechanisms Occuring in the Stove 

A known amount of charcoal is loaded into the stove grate and ignited. 

Air flows in by natural convection through the inlet opening to accelerate 

combustion; this operation is continued until all the charcoal is burned. 

During the cooking operation, most of the heat from the combustion is 

consumed to raise the temperature of the charcoal to its burning point; if 

the process is assumed adiabatic, the combustion temperature will vary 

depending on the geometrical structure of the stove, the supply of air, and 

the arrangement and the amount of charcoal loaded. 

Air is naturally drawn into the stove due to the difference in pressure 

from the outside to the inside. The flow rate of air is, hence, dependent 

on the pressure difference and also on the air inlet area. 

In the combustion chamber, oxygen in the air oxidizes carbon in the 

charcoal, producing heat. The amount of heat produced varies with the 

condition of combustion: if a large quantity of charcoal is loaded and the 

air supply is not sufficient, the combustion is incomplete; on the other 

hand, if air is sufficiently supplied or oversupplied, the combustion is 

complete. The former condition yields less heat than the latter. However, 

oversupply of air tends to bring the stove temperature down. Consequently, 

heat produced by the combustion depends on the amount of charcoal and the 

flow rate of air. 

135

Heat from the combustion of charcoal diusipates by three modes: 

conduction, convection, and radiation (see Thomas, 1980). The conductive 

heat transfers through the wall of the stove and the wall of the pot. During 

the transient state some heat is stored in the stove material, resulting in 

an increase of the temperature. This amount of stored heat varies directly 

with the mass and the temperature increment from its initial value to the 

steady-state value. At the steady state, according to the Fourier law of 

heat conduction, heat, conducedt through the stove wall, varies inversely 

with the wall thickness and directly with the temperature gradietit across the 

wall. 

The air, after combustion with the charcoal, has a low density due to 

the increase in ;emperature. As a consequence, the exhaust air, carrying 

some heat with it, rises and leaves the stove through the gaps between the 

stove and the pot. A portion of the heat is released to the pot by 

conduction when the exhaust air (or the flame) comes into contact with the 

pot bottom; the remainder,accompanying the exhaust air out of the stove, can 

be considered as a loss. The whole mechanism here is actually natural 

convection. The flow rate of the exhaust air, hence, depends on the gap area 

and the pressi're gradient. 

The third form of heat transfer in the stove is radiation. It is the 

most important mode among the thrLe since, according to the Stefah-Boltzmann 

law, the radiative energy from a surface, having an absolute temperature 

higher than 0 0 K, varies with the temperature to power four. With the 

temperature of the charcoal or the flame much higher than the temperature of 

the pot, the net flux of radiative energy from the flame to the pot is 

enormous. However, the net energy flux intercepted by the pot bottom decreases 

as the distance between the flame and the pot increases. The change in the 

net flux due to the change in the distance is commonly explained by the 

concept of view factor, which is simply defined as the ratio of the radiation 

from one surface intercepted by another surface to the total radiation from 

the first surface. The pot bottom, as the second surface in this definition 

gains the radiative energy from the charcoal, which acts as the first surface, 

1 y the amount proportional to the view factor from the charcoal to the pot. 

If the radiation is envisaged as energy particles or photons propelled 

outward from the flame in a random manner, the chance that the photons will 

hit the pot bottom diminished when the distance increases and the view factor 

decreases. Consequently, the radiative energy gained by the pot decreases 

with increasing distance. 

The above view of the heat transfer mechanisms in the stove lays the 

basis of modelling. It will include all the essential characteristics of the 

stove studied in experiments: the grate hole area Ag, relating to the natural 

convection of inlet air; the stove mass weight M s , connected to the heat 

stored in the material of the stove; the gap height G, associated with the 

natural convection of t:,e exhaust air; the wall thickness D, related to the 

heat conduction; and th! distance from grate to pot H, pertaining to the 

radiation (see Fig. 6.1). 

136

Fig. 6.1 Structure of the ideal Biomass cooking stove: 

a - pot stand; 

b - exhause gap; 

c - grate to pot distance; 

d - combustion chamber; 

e - grate; 

f - ash compartment; 

g - opening for inlet air; 

h - stove base; 

i - stove width. 

137

Mathematical Modelling 

Heat from the combustion dissipates, as previously explained, by 

conduction, natural convection, and radiation. Heat fluxes resulting from 

these modes of heat transfer may be estimated from some mathematical 

relations available in many standard textbooks concerning heat transfer. 

Examples are books by Bird et al.(1960), Thomas (1980), Bennett and Myers 

(1974). 

For conduction of heat through solid slab, heat flux can be calculated 

from the Fourier's law of heat conduction. If the slab has a thickness of D, 

the two surfaces at different temperature T 1 and T 2 (T 1 > T 2), and its 

thermal conductivity of k, heat flux qcond at steady state, according to the 

Fourier's law, can be expressed as: 

qcond = k(T 1 - T 2 )/D (1) 

In the process of natural convection, it has been known that this mode 

of heat transfer is strongly dependent on the value of Grashof number, which 

is proportional to the temperature difference. The analysis of natural 

convection of fluid between two parallel infinite plates at different 

temperatures, aligned with the gravitation direction, shows the velocity of 

the buoyant fluid to vary directly with the Grashof number (Bird et al, 1960). 

Undoubtedly, the natural convection between two plates is quite different 

from what actually occurs in the stove. However, it exemplifies the aforementioned 

fact that natural convection is a function of the Grashof number. 

or, as a consequence, due to the definition of the Grashof number, a function 

of temperature difference, that is: 

Vconv = f(Gr) (2) 

in which vconv is the velocity of the buoyant gas and Gr is the Grashof 

number. 

Heat fluxes due to radiation between two isothermal surfaces 2, a is 

factors between the surfaces are known, can be calculated from 

qrad = oF 1 (r - Ti) 

2 (3) 

in which qrad is the radiative heat flux from surface 1 to surface 2, a is 

Stefan-Boltzmann constant, F 1 2 is the view factor from surface 1 to surface 

2, and T 1 and T 2 are the respective temperatures of surfaces 1 and 2. 

For radiation between two circular discs of equal diameter, the view 

factors between the two discs have been calculated analytically and plotted 

against the ratio of the diameter to the distance between the discs (Thomas, 

1980). If the diameter is unchanged, the view factor is approximately 

proportional to the inverse of the distance H: 

F 1 2 = 1/H (4) 

138

To simplify the modelling, the following assumptions are made: 

1. Flame temperature is constant (about 800*C). 

2. Time and fuel required to increase the temperature of the fuel bed 

from its initial value (i.e. ambient temperature) to the final temperature 

at 800C are negligible. 

3. The rate of combustion is proportional to the air mass flow rate 

into the bed. 

4. Density of the stove material p, and heat capacity 4p, thermal 

conductivity k are constant. 

5. The wall thickness is uniform. 

6. The diameter of the grate and the diameter of the pot are constant. 

7. Only part of the radiation is considered as useful in heating, the 

other modes of heat transfer contribute to heat loss. 

Since the air flow into and out of the stove is by natural convection, 

the velocity of the air is a function of the Grashof number. The relation 

between vconv and Gr in this situation can be obtained experimentally. 

However, no experiments with the purpose of procuring such relations have been 

performed. In order that the modelling can proceed, the relationship has to 

be assumed. For simplicity, a linear relationship between the velocity of 

buoyant gas and the Grashof number is adopted: 

or 

Vconv = (constant) Gr (5) 

Vconv = (constant) (Tflame - Tamb) (6) 

in which Tflame and Tamb are the respective temperatures of the flame and 

the surroundings. 

Due to assumption 1, that the flame temperature Tflame is ccnstant, 

Fig. 6 indicates that the velocity of the upflow gas is constant: 

Vconv = constant (7) 

For air inlet, the air has to pass the grate holes before it is 

consumed in the combustion process. With constant air velocity, the volume 

flow rate is proportional to the grate hole area Ag. Consequently, the mass 

flow rate of the inlet air is also in proportion to the grate hole area. 

Assumption 3 and the argument in the previous paragraph give the 

consumption rate of charcoal in the following form: 

- dm c/dt = aA (8) 

in which mc is the mass of charcoal, t is time, and a is a constant. 

139

Similarly, the volume flow rate of exhaust gas, which leaves the stove 

through the gap, varies directly with the gap area. It was found later that 

the gap area changes in a linear fashion with the gap height G. Thus, 

volume flow rate, or, in other words, the mass flow rate of the exhaust gaL 

is proportional to the gap height G. Since the flame temperature is assumed 

constant, the heat loss due to this process then varies linearly with the 

gap height G. If Qconv is the rate of heat loss, 

in which B is a consti't. 

= 

Qconv BG (9) 

At the initial time the temperature of the stove material is the same 

as the ambient temperature; the temperature increases to a certain value at 

steady state. The constancy of thermal conductivity indicated in assumption 

4 assures a linear temperature profile across the stove wall when the system 

is steady. Since the flame temperature is constant for any thickness of the 

wall, the temperature difference across it is also constant. Heat stored 

in the stove material can, hence, be calculated from the average temperature, 

which is unchanged for any stove. With the assumption of constant heat 

capacity, the total heat absorbed by the stove mass Qabs is proportional to 

the mass m. Dividing the total absorbed heat with the total heating time 

yields the rate of heat absorption Qabs: 

Qabs = Ems (10) 

in which c is a function of time and physical properties of stove material. 

For convenience, e is assumed constant. 

The rate of heat transferred through the wall by conduction Qcond is 

estimated from Eq (1): 

Qcond = kA(Tflame - Tamb)/D (11) 

in which A is the total surface area of the stove wall. 

Since the density of the stove material is p, and the wall thickness 

is uniform, the area A can be related to the mass and the thickness D: 

m s 

m s = pAD (12) 

Substitution of Eq (12) in Eq (11) gives 

or 

Qcond = k(Tflame - Tamb)ms/pD 2 (13) 

Qcond , 6ms/D 2 

in which 6 = k(TfJame - Tamb)/P (15) 

Total heat generated by the combustion is proportional to the rate of 

combustion if heat of combustion is constant: If Qcomb is the rate of heat 

generated, equation (8) gives 

140 

(14)

Qcomb , a*Aq 

in which a* is the product of a and the heat of combustion per mass of 

charcoal consumed. 

(16) 

Subtraction of conductive heat and convective heat from the total heat 

generated from the combustion would give the radiative heat: 

Qrad = a*A - OG - Em - 6m /D 2 

(17) 

in which Qrad is the rate of heat transfer by radiation. 

Not all the radiative heat is used in boiling water. The amount of this 

heat varies with the view factor between the pot and the charcoal, which, 

according to Eq (4), is approximately in proportion to the inverse of the 

distance between the grate and the pot bottom H. If h is the rate of hea. 

supplied to the water, 

in which y is a constant. 

Qh = YQrad/H 

Substitution of equation (17) into equation (18) gives 

s 

(18) 

Qh = y(a*Ag - OG - Em - 6ms/D 2 )/H (19) 

s 

Fig. 19 will be used as a means of estimating the heat in bringing the 

temperature of water from the initial state to the state of boiling, and 

in evaporating water. 

Period of heating water 

In this period, water is heated from the ambient temperature Tamb to 

the boiling point Tboil. Since the cooking pot used in this work is made of 

aluminium which has the property of good thermal conduction, the heat that 

is intercepted by the pot is partially transferred to heat the water and the 

remainder is lost through the pot surface. If k and QI are the rates of 

heat absorbed by water and heat loss respectively, then 

= 

Q1 Qw + QI 

Part of the heat that is absorbed by the water prior to its boiling is given by: 

Qw = mwocpwdTw/dt 

in which mo is the initial mass of water, cpw is the heat capacity of water, 

and Tw is the water temperature at time t. The heat loss through the pot 

surface is given by: 

(20) 

(21) 

Q = hS(Tw - Tamb) (22) 

in which h is the heat transfer coefficient, and S is the surface area of 

the pot. 

141

Substitution of Eqs (21) and (22) into Eq (20) give 

h = m.oCpwdTw/dt + hS(Tw - Tamb) (23) 

The solution of this differential equation is 

Tw = BI/B 2 + (Tamb - Bl/B 2) e-B2t (24) 

in which B 1 = (Qh - hSTamb)/woCpw (25) 

B2 = hS/mwocpc, 

(26) 

Substitution Eqs (19), (25), and (26) into Eq (24), and then rearranging 

the result of substitution, one gets 

T = T amb + y(* Ag - G - Rms - ms/D 2 ) (i e -B 2 t( 

hSH - (27) 

Eq (27) is used to estimate the time required to increase the temperature 

of water from the ambient value to its boiling point. 

Period of boiling 

At boiling, the water molecules begin to move turbulently and become 

loosely bound. Eventually, some of the water molecules with enough kinetic 

energy will be able to escape from the water surface in the form of vapor. 

If the rate of heat consumed in evaporating water is mvhfg, the overall energy 

balance is 

H (a*Ag - OG - em s - 6ms/D 2 ) - hS(Tboil Tamb) = 4hfg (28) 

in which kv is the rate of evaporated water and hfg is the latent heat of 

vaporization. 

If t 2 is the total time used in the experiment and t I is the time 

required in heating the water from its initial state to boiling, then the 

total heat consumed in boiling can be obtained by multiplying Eq (28) with 

t 2 - tl: 

[H (*Ag - - Em s - 6ms/D 2 ) - hS(Tboil - Tamb)] (t 2 _ t 1 ) 

= mvhfg(t 2 - t I ) (29) 

The results in parts A and B are used to estimate the efficiency of 

the stove. 

Efficiency of stove 

The heat utilization or the efficiency of the cooking stove n is 

defined as the ratio of the heat consumed in heating and boiling water to 

the total heat input into the system. Since the rate of combustion is not 

a function of the charcoal mass as seen in Eq (8), the efficiency q can be 

expressed as 

142

Qsens + khfg ( t2 

aA AH t 2 

l ) 

- t 

in which AH is the heat of combustion, and Qsens is the sensible heat of 

water in increasing the temperature from the ambient to the boiling point. 

The time required to increase the Lehiperature of water, in the experiment, 

is usually less than the time required to reach the boiling point. 

Although the difference between the heating time and the boiling time is 

not really insignificant, the sensible heat will be excluded from Eq (30). 

This action is done for two reasons: one, the mass of water is not taken as 

one of the variables in this work; two, including the sensible heat adds at 

least one more variable, which not only complicates the evaluation of 

parameter, but may also obscure the effect )f other variables. Furthermore, 

heat loss through the pot surface will be neglected in Eq (29). 

efficiency of the stove becomes 

Hence, the 

Y(a*Ag - $G - ems 2 

- 6ms /D ) (t2 - t1 ) (31) 

aA HAH t2 Eq (31) can be simplified where the constants are lumped together: 

t2 - t t2 - t1 a t2 -t 1 ms t2 - t1 = a 2H _ a2 AHt a3 ms( A2Ht2 ) -a4 2 AH (32) 

in which a, = y (33) 

a 2 

a 3 

a 4 

(30) 

= y /aAH (34) 

= ye/aAH (35) 

= y6/aAH (36) 

Eq 32 is actually linear with respect to the parameters. This fact 

can facilitate the method of evaluating the parameters. 

B. EVALUATION OF PARAMETERS 

Since Eq 32 is linear, the least square method or the method of 

multiple linear regression would be appropriate in evaluating the parameters 

al, a2, a 3 , and a 4 . However, with either method, Eq 32 has to be rearranged 

into the standard form: 

= alX 1 + a 2X 2 + a 3X 3 + a 4X 4 

in which X 1 = (t 2 - tl)/Ht 2 (38) 

x 2 

X 3 

(37) 

= X1G/Ag (39) 

= Xlms/Ag (40) 

= X 3/AgD 2 (41) 

143

The method of multiple linear regression, which can be found in many 

textbooks on Statistics (e.g. Walpole and Myers, 1972; Hoel, 1971), is 

adopted in this work. The input data of those physical factors described 

earlier are selected from the previous baseline survey which consists of 

thirty-six bucket-type stoves. All the calculations are done by an INTRA 

microcomputer; the program is written in BASIC. The correlation coefficient 

from the calculation vith boiling time of 30 minutes is found to be very 

small, indicating the fluctuation of the data. This fluctuation is believed 

to be due to the fact that the stoves, obtained from thirty-six different 

locations throughout the country, have variable properties and composition 

which violaces one of the assumptions. 

Another reason for poor fitting can be due to some of the assumptions 

used in developing the model. For example, e, which is the function of time 

and physical porperties of the stove, may have a severe effect on the stove 

behavior. This function is, however, difficult to obtain. The number of 

parameters in the model of the bucket stove, which is a complicated system, 

may not be sufficient; and some of the other effects such as the 

sensible heat excluded from the equation of efficiency may be required. 

But too many parameters obscure the effect of variables under investigation 

and can, in some situations, lessen the value of the model. Another violation 

of the assumptions is the nonuniformity of the wall thickness; the Thai 

bucket stove generally has its wall area thicker near the base than that near 

the top of the stove. 

An alternative approach for the application of the model is to group 

the stoves that have similar effects, such as a group that would give a 

correlation coefficient greater than 90%. This is done with the INTRA 

microcomputer, the grouping is carried out randomly. The result from this 

analysis shows that the maximum of fifteen stove combinations would 

compromise the requirement. One of such groups is shown in Table 1 for which 

the correlation coefficient is 94%; the values of al, a, a 3 , and a 4 are 

653.8 em, 5,717.01 cm 2 , 26.23 cm 2 /kg, and 5,282.13 cm / g, respectively. 

This group is LSed in the next step; i.e. studying the performance of the stove 

when one of the variables is changed while others are kept constant. 

C. MODEL APPLICATION 

The model developed in the preceding sections is kept as simple as 

possible; it requires minimum knowledge of the stove characteristics. In 

this section, the simulation of the model is carried out to investigate 

the effect of each variable on the efficiency of the stove. 

Prior to simulation, owing to the geometrical variation of the hand-made 

stoves sold in the Thai market, an ideal stove is required to represent the 

actual ones. The stove is simply idealized as being enclosed by two 

coaxial truncated cones as illustrated in Fig. 6.2; the stove thickness 

(i.e. the distance between the cones) is assumed uniform. When the concept 

of similar triangles is applied to the ideal stove (see Annex 3),the 

following relationships are obtained: 

144

% 

I' i I 

1i1 

- I I 

/ , :I' '1 

k- 'pe- 

I, 

Fig. 6.2 Geometry of the ideal stove: the dimension of the outer 

and the inner cones are respectively symbolized by 

capital and small letters.

m= 12 (Dt g) d3) - - d3)) (Ae + A 1 )D] (42) 

Dt = dt + 2D (43) 

D(dt - dg) 

Db = db + D - H (44) 

Dg = dg + 2D (45) 

in which Dt, dt are the respective outside and inside diameters of the stove 

at the pot stand, 

Db, db are the respective outside and inside diameters of the stove 

at the bottom, 

Dg, dg are the respective outside and inside diameters of the stove 

at the grate position, 

Ae is the gap area, 

Al is the area of opening for the inlet air. 

There are seven variables that completely fix the geometry of the stove; 

they are: the three inside diameters dt, dg, and db; the wall thickness D; 

the grate-to-pot distance G; the gap area Ae; and the area of the opening for 

the inlet air A 1 (the dimensions of D, H, Ae and Ai are shown in Fig. 61.). 

Among these seven varibles, A e and Ai are not the variables in the model. 

Therefore, they have to be related to other variables. Fig. 6.3 and 6.4 

illustrate the relationship between the air inlet area Ai and the grate hole 

area Ag, and between the gap area A e and the gap height G, respectively. 

When straight lines are drawn through these points, it is found that 

Ai = 0.82 Ag and Ae = 48 G. Substitution of these relationships in Eq (42) 

givesm = [2D D (D3 - dt) - (Db - 2 

d)} - (48G + 0.8 Ag)D] 

12(D t - Dg) P b b9 (46) 

The efficiency of the stove in Eq (32) also depends on the time tl 

required to heat the water to the boiling point. From Eq (27), the estimation 

of t 1 can be achieved if B 2 is known. This implies the necessity of 

evaluating B 2 . There are two ways that the value of B 2 caa be estimated: one 

way is to employ the relation in Eq (26), and the other is to utilize the 

available experimental data. The first method requires the values of the 

heat transfer coefficient h and the heat transfer area S; both values have 

to be estimated. To avoid such approximation of h and S, and in order to 

fully utilize the experimental results, the second method is chosen. 

Substituting t and Tw in Eq (27) by tI and Tboil, and then rearranging 

it, one gets: 

1 

(Tboil - Tamb) hSH 

t T2 [B y(a*Ag - 8G - ems - 2 ) ] 

(47) 

146

150 

100 

50 

4+ 

w + 

+ 

+ + +e 

+ 

0 5b 16o iA 

Grate hole area, cm 2 

Fig. 6.3 Relationship between the area of the opening for inlet air 

and the grate hole area. 

147

2001 

160" 

N 

U) 80-12 

0 

Fig. 6.4 

0~5 .0 1.5 2.0 2.5 3.o 

Gap height, cm. 

Relationship between exhaust area and gap height. 

148

With the relationships in Eq,(33) to (36) and the fact that a* = aAH, 

Eq (47) can be expressed as: 

x = (I = e-B 2 tl)/p (48) 

in which x = H/(alAg - a 2G - a 3m s - a 4ms/D 2 ) (49) 

p = (Tboil - Tamb)hS/a AH (50) 

Eq.(48) indicates that x increases from zero to 1/p as t, increases 

from zero to infinity. With the values of al, a a3, and a4 obtained in 

the section of parameter evaluation, x can be calculated for each pot in 

Table 6.1 and then plotted against the heating time tI . An exponential curve 

is drawn through the points as shown in Fig. 6.5; it appears to approach 

- 

the value of x = 3.5 x 10 4 when t, approaches infinity. Hence, 1/p equals 

3.5 x 10 - 4 . B2 , evaluated at t, of 1$ minutes, is found to have the value 

of 0.07; this value, according to Eq.(26), implies that in the heating 

period, energy stored in the water is much greater than heat lost through 

the pot surface. Since the time to heat water is usually less than the 

boiling time, energy used in heating would be less than energy used in 

boiling. Consequently, the loss of heat through the pot surface, in the 

period of boiling, is much smaller than the energy consumed in evaporating 

water. Neglecting the heat loss in deriving the equation of efficiency is, 

therefore, approved and acceptable. 

To estimate the mass of stove by Eq. (46), the density of the stove 

material, which is fired clay, is required. But, as the stoves tested in 

this work come from various places in Thailand, each stove would have been 

subject to particular and different treatment during the process of 

manufacture. This, of course, would cause a variation of density. Moreover, 

the stoves, after being tested, are still in good condition, so they are 

kept for further use. The density of the stove material, necessarily, has to 

be estimated from other clay products of similar make such as bricks. It is 

found that bricks have densities ranging from 103 to 128 lb/ft 3 (Perry and 

Chilton, 1973). As an illustration of model simulation, the density of the 

3 - 3 3 

stove material is taken to be 110 lb/ft or equivalent 1.76 x 10 kg/cm . 

The following dimensions are chosen to represent the standard 

dimensions of the stove: H = 10 cm, D = 5 cm, G = 1.8 cm, d = 15 cm, 

dt = 20 cm, db = 10 cm, and A = 80 cm 2 . These values are In the range of 

the dimensions of the stoves Investigated in the present work. The stove 

with this standard structure has the efficiency of 28.73% when boiling is 

kept for 30 minutes, the mass of 10 kg and the time to boil of 19.9 minutes. 

With the above standard values of geometrical dimensions, and the values2 of the parameters previously obtained (i.e., a = 653.8 cm, a2 = 5,717.01 cm 

1 

a3 = 36.23 cm 2 /kg, a4 = 5,282.13 cm 5 /kg, and B2 = 0.07), the simulation is 

carried out to study the effect of each variable on the efficiency, the mass 

of the s'ove, and the time to boil. 

149

Table 6.1 Group of stoves that have similar behavior 

Stove 

No. 

Time to Grate-to Grate hole 

Boil Pot Distance area 

Gap 

Height 

Stvoe 

Weight 

Wall Efficiency 

Thickness 

(min) (cm) (cm2) (cm) (kg) (cm) (%) 

2 21.7 12 112 2 12.2 6.3 24.96 

3 22.3 12 112 1.8 8.7 3.9 25.7 

4 18.8 12.2 112 1.5 12.8 6.3 28.19 

6 18 12 69 1 8.6 6 28.83 

8 27 9 48 1.5 8.1 4.5 24.07 

12 22.6 9 65 2 7.2 4.8 29.02 

15 24.6 9 65 2 10 6 27.21 

19 23.8 11 94 2.5 10.5 6.8 23.94 

22 23.3 11 85 0.7 9.5 3.3 28.11 

28 20.1 10 74 2.3 12.2 4.5 25.1 

29 20 11.5 74 2 13.2 6 25.85 

31 16.7 12 94 0.5 11.8 6 32.39 

33 18.3 12 94 0.5 6.7 3.3 30.51 

35 20 10 70 1.9 10 4 27.7 

36 17 9.7 57 0.9 8 4.5 33.35 

150

6. 

5. 

X X O-4 4. 

V.x O 4 3. 

2 

1. 

0 

0 10 20 30 40 50 60 70 80 

Time, min. 

Fig. 6.5 Relationship between variable X, defined in Equation (49), 


X ....Experimental data; solid line ..... fitted curve. 

151

Effect of the grate-to-pot distance Y 

When the distance between the grate and the pot increasei, the model 

predictsa rapid drop of efficiency, increases of stove material and time to 

boil Fig. 6.6. As previously mentioned, the decrease in efficiency (curve n) 

when H increases, can be explained with the concept of view factor. As 

H increase the view factor decreaEas, causing the reduction of radiative 

heat being intercepted by the pot from the fiame; most of the heat is lost 

when the charcoal is very far from the pnt. Since the rate of heat supplied 

to the water in the pot is reduced due to the increase of H, the water in the 

pot will require a longer time to reach the state of boiling (curve tl). 

Geometrically, nny increp nf the diqtance between the grate and the 

pot, while keeping other characteristics unchanged, results in a comparatively 

larger increase in the total height of the stove. This implies a bigger 

size of stove; consequently, more stove material is required as predicted by 

the model (curve ms). The increase of the mass also affects the efficiency 

of the stove: more energy would be accumulated as heat in the stove material 

when the mass increases. Moreover, with the constant wall thickness, it 

means larger heat transfer area for the conduction; hence, more heat is lost 

to the environment. This effect, in addition to the effect of the reduction 

of view factor, further lessens the efficiency of the stove. 

Fig. 6 gives another impression that the model is improper at low values 

of H where the efficiency appears very high. However, such a condition is 

not likely to happen in practice, since a low H implicates a small combustion 

chamber, which, if too small, cannot hold sufficient charcoal to run the 

test. Hence, reality will set the limitation of the model. 

Eff2ct of the stove wall thickness D 

As illustrated in Fig. 7, an increase of wall thickness, up to a certain 

value, tends to improve the performance of the stove (curve T). Further 

increase in the thickness causes a slight reduction of the efficiency. Heat 

loss due to conduction across the wall is high in the stove with thin walls. 

Increasing the thickness hinders the conductive heat transfer, but, at the 

same time, promotes the loss of energy to be stored in the wall material. 

These two phenomena work simultaneously and antagonistically. The initial 

increase in wall thickness in Fig. 1.7 indicates the reduction of conduction 

is greater than the increase in energy stored in the material. As the 

thickness is increased, the relative rate of heat conduction is lower than 

the rate of energy being accumulated, resulting in the drop in efficiency. 

The choice of wall thickness not only helps improve the stove 

performance, but it will also help in savi'ig raw material which, in this case, 

is clay. The increase in wall thickness r:eans more clay is required in 

making the stove (curve ms). An increase of the wall thickness from 2 to 

10 cm causes the mass of the stove to increase from 5 kg to more than 45 kg: 

an increase of wall thickness by 5 times induces an increase of the mass 

by about 10 times. I the wall thickness is kept at 6 cm instead of at 

10 cm, two stoves can be manufactured instead of one. Moreover, the two 

stoves with the thickness of 6 cm have higher efficiency of performance 

than the one stove with the thickness of 10 cm. 

152

40- 16 100- 

m I 

30 12 55 -- /0 

0 8 45 

0- 4- 25- 

4 60 12 14 

Height from grate to pot, cm. 

Fig. 6.6 Model prediction of the effect of grate-to-pot distance 

on the stove efficiency (n), stove mass (ms) 

to boil , and 

(t8). 

time 

153

5j 50 - 30" 

40- 40 

S 

'.44 

25 

30 20 

' 

20 'n 20- 

10510 

1 10 

]. 

" 

/°3 

iss I 

" 

IIII 

2 4 6 8 

Wall thickness, cm. 

I 

t 

s 

10 12 14 

the effect of wall thickness on 

Fig. 6.7 Model prediction of 

the stove efficiency (), stove mass (ms ), and time 

to boil (t1 ). 

154

Curve t 1 shows the change of time as the thickness of the wall changes. 

The increase of the thickness from 1 to 4 cm reduces the time to boil from 

36 to 20 minutes. A slight increase of time to boil is seen when the wall 

thickness is larger than 6 cm. This behavior can be explained by the 

concept of antagonism between the heat conduction across the wall and the 

heat accumulated in the wall material as described before. 

Effect of the inside diameter of stove at the bottom db 

As the inside diameter of the stove at the bottom db increases, the 

model predicts only a slight increase in efficiency, a slight decrease in 

time to boil, and a reduction of stove mass (see Fig. 6.8). Geometrically, 

the change of only db will mainly affect the ashing compartment without having 

any effect on the combustion chamber, which is the major part of the stove 

supplying heat to the water. An increase in db reduces the ashing chamber 

and, consequently, the stove mass. When db increases from 7 to 15 cm, the 

stove weight decreases from 15.9 to 14.3 kg (curve ms) - about 1% decrease 

in mass. The change of efficiency in this case is, conclusively, caused by 

the change in the amount of energy stored in the mass of stove. 

Although the increase in the inside diameter of the stove at the bottom 

lessens the raw material, the choice should depend on the structural strength 

and the area of the opening for the inlet air. 

Effect of inside dicaneter of the stove at the pot stand dt 

The model prediction of the effect of inside diameter of the stove at 

the stand dt on the stove performance, the mass of stove, and the time 

required to increase the water temperature to its boiling point is illustrated 

in Fig. 6.9. When the inside diameter at the pot stand is slightly greater 

than the grate diameter (d = 15 cm), the efficiency is low (curve n), the 

mass of the stove (curve m) and the time to boil (curve tl) are high; at 

this value of dt, the distance between the bottom and the grate is very large, 

resulting in high requirement for raw material and, as a consequence high 

accumulation of energy in the stove material. The high loss of energy from 

the combustion due to the stove material causes the reduction of energy 

supplied to the stove; hence, the time required to boil is high. The increase 

in dt will reduce the distance between the grate and the bottom, which 

simultaneously reduces the stove material. Consequently, less energy is 

stored in the stove material and the time required to boil is less. 

Effect of Gap Height G 

The model prediction in Fig. 6.10 indicates that as the gap height G 

increases, the efficiency n (curve n) decreases linearly at first and more 

rapidly at a later stage. The decrease of efficiency implies the increasing 

loss of energy carried out by exhaust gases due to the process of free 

convection. The larger the gap height, the larger the gap area, and the 

greater the loss of energy through convection. However, this loss is 

counteracted by the loss of energy accumulated in the mass of the stove, which 

decreases linearly wit' the increase of 6 (curve ms). The rate of change of 

155

16" 32 

• 30- ".s 

20- t 

5 

o- 

0 

- 

0 

15- A 28c;" 

. 

- 

 

. . . 

o 0 0 T -426 

141 21 

II I I I 

2 4 6 8 10 12 14 16 

I-iside diameter of stove at the bottom, cm. 

Fig. 6.8 Model prediction of the effect of inside diameter of 

stove at the bottom on the stove efficiency(q), stove 

mass (ms), and time to boil (tl). 

156

50 

50 _ 

40 40 - 

30 

*d30 0 30- '\% 

4 Ca 

g~ 2 20 22o 

1 

10 10 14- 

,10 1 

Fig. 6.9 

-- 

1. ] 

S 

16 18 20 22 24 26 28 30 

Top diameter, cm. 

Model prediction of the effect of inside diameter of 

stove at the pot stand on the stove efficiency (r), 

stove mass (ms), and time to boil (t 1). 

157

60 

50 

1( 

50- . 40 

30- 

o 1> . 

" 

u 

20 

20" 1 

14 -- 1 

II 

0 1 2 3 4 

Gap height, cm. 

Fig. 6.10 Model prediction of the effect of gap height on the 

stove efficiency (n), stove mass (ms), and time to 

boil (tI). 

158

these losses is relatively constant at small G; but at large G, the natural 

convection becomes dominant and causes the rapid drop of the efficiency. 

Since loss of energy increases when G is inacreasing, the time to boil under 

these conditions will increase with G (curve tl). 

Effect of grate diameter 4i 

Fig. 6.11 illustrates the effect of grate diameter on the stove 

efficiency, stove mass, and time to boil. At the grate diameter of 10 cm, 

the effic 4 .ency is about 32% which is approximately 3% greater than the 

efficienc of the standard stove; the efficiency drops slowly from 32% to 

28.7% when the grate diameter increases from 10 to 15 cm (curve n). As d 

is greater than 15 cm, the efficiency rapidly diminishes to 20% at dg =1 cm. 

The change in efficiency can be explained in relation to the change in 

mass (curve ms). When the value of dg is 10 cm, the stove mass is small, 

about 18 kg. At this value of dg the volume of the ashing compartment is very 

small, and in effect it represents a stove without an ashing compartment. 

This results in the fresh surrounding air coming into direct contact with the 

flame. The efficiency is improved not only by good-combustion, but also by 

the reduction of energy stored in the stove material. Providing the area of 

the opening for the inlet air has no effect on the air supply to the flame, 

an increase in grate diameter will increase the size of the ashing chamber 

and consequently, the stove mass is increased. Energy accumulated in the 

stove material increases. Moreover, the increase in material causes the 

increase in heat transfer area, which promotes heat loss due to conduction 

through the wall. These effects reduce the efficiency of the stove and at 

the same time increase the time to boil (curve ts). 

Effect of rvau;c i avea Aa 

The grate hole area,according to the assumption in modelling, controls 

the rate of air supply to the combustion. An increase in grate hole area 

thus improves the air supply which results in better combustion and, as 

consequence, good performance of the stove (curve q in Fig. 6.12). The stove 

mass decreases as Ag increases. This reduces the energy stored in the stove 

material (curve ms). Due to good heat supply to water, the time to boil 

decreases (curve tl). 

It should be noted that the grate hole area cannot be increased without 

limit. The grate diameter, and the strength of the grate are factors that 

will constrain the grate hole area. Since the diameter of the grate of 

standard stove is 15 cm, the maximum area provided by the grate is about 

176 cm 2 ; the value of Ag greater than 176 cm 2 would be impractical. If the 

strength of the grate is considered, the grate hole area will be much less 

2 

than 176 cm . 

The comparative study, illustrated in this simulation, is based on the 

assumption that the flow rate of air depends only on the total area of grate 

holes; this, of course, implies that Ag increases because of the increase in 

the number of grate holes without altering the hole diameter. If the hole 

159

40- 40- 401 

30 _ 

• 

S2CL 0 20- 

30 3 0: 

0 .8 

2Q_ 

I1 

S 

IuI 

6 

Iu 

8 10 12 

Grate diameter, cm. 

t - 

- 

/ 

/' 

14 

Iu 

19 2d 

Fig. 6.11 Model prediction of the effect of grate diameter on 

the stove efficiency (n), stove mass (ms), and time 

to boil (t 1). 

160

16 

40-50 

E30/20"-\ 

40 

14-220 t 

I I I I1 

60 80 100 120 140 160 180 

2 

Grate hole area, cm 

Fig. 6.12 Model prediction of the effect of grate hole area on the 

efficiency(n), stove mass (ms), and time to boil (t 1). 

161

diameter changes, the resistance of the hole to the air flow will be affected; 

the parameter in Eq (8), therefore, has different values at different hole 

diameters. This point should be noted in comparing any stove efficiency. 

D. DISCUSSION AND EVALUATION 

Many assumptions have been introduced in developing the model and the 

bucket stove in this section. These assumptions are proposed to simplify the 

mathematical complexity and to relate major factors that are studied 

experimentally. As a consequence, the model prediction deviates from 

observation under some experimental condltions. This preliminary model, in 

the future, will be modified to provide a more detailed eyplanation. 

The process of combustion is very complex; the composition of the 

combustion products and the heat of combustion are strongly affected by the 

amount of air supplied to the stove. In the model, it is assumed that heat 

of combustion and the composition of the exhaust gas are not changed--regardless 

of any variation in air supply. This assumptioa is valid only when combustion 

is complete. Such complete combustion, however, in achieved only if sufficient 

air is provided to the stove. If air is undersupplied (which is caused by a 

small total grate hole area) heat of combustion is reduced and efficiency is 

also reduced. But if the grate hole area is too large, the air to 

oversupplied. Although the combustion is complete for this condition, a large 

amount of energy generated by the combustion is lost in increasing the 

temperature of the excess air. Consequently, a drop of efficiency is expected. 

As the model does not account for this effect, the predicted efficiency keeps 

on increasing with the grate hole area. A detailed study of the combustion 

mechanism in relation to the grate hole area is necessary for any modifications 

of the model. 

In modelling the stove, the effect of the grate diameter on the view 

factor has been neglected. It has already been mentioned that the view factor 

between two circular discs with equal diameters varies with both the diameter 

and the distance between the discs. Since radiation is the major energy 

supply for cooking, the inclusion of the grate diameter into the equation for 

view factor estimation might stress the importance of the grate diameter on 

the efficiency. 

Another point that needs to be considered in improving the model is the 

energy required to increase the water temperature to its boiling point. The 

present model assumes that the time to boil is small and hence not much 

energy would be utilized in this process. However, the model predicts that 

the time to boil in some cases is large, indicating that a massive amount of 

energy has been consumed. For example, if the time to boil and the boiling 

time are 20 and 30 minutes, respectively, providing that the rate of heat 

supply from the combustion is constant and heat loss is small, then the 

ratio of heat used in heating up water and in boiling is 2 to 3. With a 

long time to boil, it is important to include heat consumed in increasing 

the water temperature when efficiency is being calculated. 

162

Although the present model is based on many assumptions, it can shed 

light on theunderstanding of interactions among the stove characteristics 

that influence stove performance. This model should give some basic idea 

of how the stove would perform. For example, the model predicts that the 

grate-to-pot distance, which contributes the major part of efficiency, 

strongly affects the performance of the stove. If it is large, the 

efficiency decreases, but if it is small, the stove will perform better. 

However, result from the experiment show that this is not exactly true: the 

performance becomes poor when the grate-to-pot distance is smaller than a 

certain value. This is mainly due to radiative loss through the gaps. 

The thickness of the stove wall also strongly affects stove performance. 

If the wall is too thick, the efficiency is reduced. The same effect is 

predicted if the wall is too thin. The stove will exhibit the best 

performance at a particular value of thickness. 

With a large grate hole area, the stove performs better than 

that with a small grate hole area. This is due to the assumption that 

air flows into the stove at constant velocity; hence, the volume or mass 

flow rate of air is proportional to the grate hole area. The model, however, 

neglects to take into account the insulation effect of the grate. A 

large grate hole area implies a high loss of radiative heat from the combustion 

chamber to the ash chamber. As a consequence, a stove with a 

grate hole area larger than a certain value could perform poorly. The 

insulation effect of the grate should be considered in the model improvement. 

Conclusions 

The model, although based on many assumptions, can give us an understanding 

of the interactions of stove geometry on the performance. The 

dependence of stove efficiency on the grate-to-pot distance can be explained 

in terms of radiative heat obtained by the pot. Increasing gap height 

causes a poor stove performance, indicated by the model as the result of 

high convective heat loss through the gap. Conductive heat loss, predicted 

by the model, is severe in the case of insufficient thickness of the stove 

wall; the stove would perform better if wall thickness is increased. However, 

if the wall is too thick, the model indicates that a large amount of 

heat is stored in the stove material, resulting in a drop in stove efficienc). 

As already discussed, the model can be modified to yield better predictions. 

The modifications should be performed according to the recommendations 

in the previous section. 

163

Chapter 7 

Stove Models Developed

STOVE MODELS DEVELOPED 

This chapter presents the results of improvement of five generic types 

of biomass household cooking stoves. 

Based on commercial stove testing and analysis of results, experience 

gained during stove collections, stove construction and.modifications in the 

laboratory, and numerous contacts with stove users and manufacturers, the 

general requirement for the improved cooking stove concept, particularly 

within Thailand, can be stated as follows: 

a) That the improved stove shall be designed to accommodate as many 

various sizes and shapes of pots and pans as possible. 

b) That the improved stove shall reduce the time duration of cooking 

or at least keep it constant. No stove with prolonged cooking time can be 

accepted, no matter how fuel efficient it may be. 

c) That the improved stove shall be made to have longer service life 

or durability. 

d) That the improved stove's portability, and construction with a single 

pothole, are desirable components. 

e) That the improved stove shall consume less fuel or at least equal 

amounts to the existing good models. 

Z) That the improved stove operation shall be conducted with ease and 

safety, including the stove's ignition, frequency of attendance, heat output 

control, refueling and fire extinguishing. 

Development then strictly followed such requirements. The design, testing 

and production of improved prototypes have yielded hardwares whose features 

and performances are presented in following sections. 

A. IMPROVED STOVE'S TERMINOLOGY 

In previous chapters, numerous discussions were made in reference to 

various stove terms. In order to avoid misunderstanding and to promote 

future stove development and standardization, drawings illustrating 

terminology are presented in Fig. 7.1 to 7.5. The five types are the charcoal 

stove, wood stove without chimney, wood stove with chimney, rice husk stove 

without chimney, and rice husk stove with chimney. All stoves, however, are 

of the single pothole type as desired by most Thai users. 

167

Pot Diameter 

r------28 cm. 

.. ..... / Bucket Handle 

S- 

- Pot Rest 

Firing Chamber 

- Stove Body 

-Grate 

Refractory Lining 

4-' Insulator 

Primary Air Inlet And 

Ash Removal Port 

Gulvanized Bucket 

Bucket Support Ring 

Figure 7.1 Drawing of improved charcoal bucket stove showing 

various parts'of the construction and terminology. 

168

Pot Diameter 

-2.4 cm. 

4-28 cm. 

.Lifting Handle 

Exhausted Gap - Pot Rest 

.4-Insulator 

--- Refractory Lining 

4.-- Stove Body 

! --- Firewood, Feeding Port 

- - Grate 

Primary Air Inlet 

And Ash Removal Port 

-Galvanized Bucket 

Figure 7.2 Drawing of improved nonchimneyed wood stove 

showing parts of the construction and terminology. 

169

Adjustable Air 

Valvet" 

e Chimney 

40 

Horse sho-, 

Contro < 

Pot #24 cm. 

Stove Body 


Aape bSmoke Cap 

Wood Fuel 

Grate 

Primary Air Inlet Port 

Figure 7.3 Drawing of developed chimneyed wood stove prototype 

showing the construction and terminology. 

170

000 0000 

000 C 

00o 

0 0 0 L 

-- -24 

Pot Diameter 

cm. 

_Pot Rest 

_ 

- 

- 

- 

Exhaust Flue Outlet 


Rice Husk Filled Chamber 

Stove Body 

Insulator 

Rice husk Flow Gap 

Tripod Base 

Air Inlet Hole 

Wooden Leg 

Outer Cone Metal Sheet 

-- _ - Ash Removal Port 

Figure 7.4 Drawing of improved nonchimneyed rice husk stove 


171

o N 

0N 

Chimney 

Rice Husk $ 

44 4JoD 0 Refractor 

Rice Husk 

Tray ' ' '. 

I Restricte Flu Exi 

Iron Grate combustion , 

' ",.Chamber'." 

Ash Removal Port A4.404 .lJ ' Lifting 

o . Hole 

Concrete Body ' ,".' -. . , , . 

. -...... .... ...... . . .. 1 

Figure 7.5 Drawing of improved chimneyed rice husk stove 


172 

N

B. IMPROVED CHARCOAL STOVE MODEL RFD-1 

The physical dimensions and characteristics of the latest improved 

charcoal stove called "RFD-l" can be described as follows: 

a) Stove weight, fired-clay body only 5.9 kg. 

fully fabricated (with bucket included) 10.1 kg. 

b) Stove height (no bucket) 25.0 cm. 

c) Top diameter (no bucket), outside 30.0 cm. 

inside 26.5 cm. 

d) Bottom diameter (no bucket), outside 19.0 cm. 


e) Vertical height from grate top to stove rim 15.0 cm. 

f) Vertical height of the pot rest portion 6.5 cm. 

g) Pots accommodation, pot diameter 16-32 cm. 

h) Firing chamber capacity after refractory lining, 

normal full charcoal load 1,240 cm., 

extra charcoal load for large cooking 2,000 cm? 

i) Grate, diameter 17.5 cm. 

thickness 4.0 cm. 

weight 0.7 kg. 

hole diameter (taper up) 1.2-1.4 cm. 

number of hole 61 

hole area 94 cm 

hole area/grate area 39 % 

j) Average thickness of inside refractory lining 1.0 cm. 

k) Exhausted gap (for flue gas outlet) 1.0 cm. 

1) Air inlet port, 5 x 11 cm. 55 cm 

m) Average stove wall thickness (including insulation 

and bucket 5.2 cmi 

n) Bucket weight 1.1 kg. 

The relationship of physical characteristics to external variables such 

as pot size, charcoal load, pot position relative to the top rim is shown 

in Table 7.1. 

173

Table 7.1 Physical characteristics of RFD-l charcoal stove relating to 

external variables 

Pot 0 Grate-to-pot Charcoal Charcoal top Exhausted Pot position 

cm distance, cm loadl gm layer-to-pot area, cm2 relative to the 

distance, cm stove rim, cm 

16 7 250 2 43.5 -7.0 

18 7.5 310 2 45.7 -6.3 

20 9 390 3 48.0 -5.5 

22 10 440 3 52.0 -4.3 

24 11 480 3 58.5 -3.2 

26 12 550 3 62.0 -2.2 

28 13 690 3 67.5 -1.0 

30 14 740 4 75.5 +0.6 

32 15 770 5 75.5 +1.0 

* the load based on high density mangrove charcoal prepared to the average 

size of 5 cm in length and 2 cm in cross-sectional width. 

Test results of developed charcoal stove (RFD-I) are shown in Table 7.2. 

Table 7.2 Average test results of RFD-l charcoal stove under different use 

conditions* 

Pot 0 No. of Charcoal Initial Charcoal Average Time to 

cm test load, g water remained burning rate boil HU % 

wt gm gm gm/min 

16 3 130 1,180 16.7 2.4 17 21.6 

20 6 240 2,190 34.0 4.2 19.5 25.4 

24 3 400 3,700 50.0 7.4 17.3 32.1 

28 3 640 5,920 90.0 10.6 22 34.2 

32 3 800 7,400 93.3 12.6 26 30.2 

* In this test, the ratio of charcoal load to initial water weight was kept 

constant at 1:9.25 based on standard tests where 400 gm of charcoal and 

3,700 gn of water were used. The water occupies approx. 3/4 of the pot 

capacity. Test durations are 30 minutes plus time to boil, all starting 

from a cold stove. 

174

From Table 7.2 the heat utilization efficiency is lowest when a very 

small load of charcoal (130 gm) is used. This should be expected because 

a large percentage of heat from charcoal input is absorbed by the stoves 

but even with such a small charcoal fuel, 1.18 liters of water can be brought 

to boil in 17 minutes. The HU begins to peak when operating the stove at 

400-640 gm charcoal, with a 24 - 28 cm pot diameter, and the amount of water 

between 3,700 - 5,900 gm. This particular range of operation represents 

the conditions used in cooking by most rural Thai families. Time to boil 

achieved by this stove based on standard comparison tests (pot #24, water 

3,700 gm, charcoal 400 gm) is 17.3 minutes which is equal to the best topline 

model in the market, as previously shown in Table 5.6. In those tests, 

the time to boil of existing commercial bucket stoves ranged from 16.7 - 32.0 

minutes and averaged 22.8 minutes. 

Regarding the stove durability, the RFD-l improved model is considered 

superior to all commercial models since the fired clay body is made of 

refractory material which can withstand thermal shock without cracking much 

better than commeicial models. For details of improved charcoal stove 

production please refer to Chapter 8. 

Recalling the six criteria of user's requirements stated earlier, it 

can be concluded with a high degree of confidence that the RFD-l improved 

model has met all those requirements. 

Fig. 7.6 and 1.7 are photo-illustrations of the sample stove made from 

actual production by a group of retrained local stove makers in Roi-et Province. 

C. IMPROVED NON-CHIMNEYED WOOD STOVE MODEL RFD-2 

This nonchimneyed wood stove, model RFD-2, has the designed purpose of 

overcoming weaknesses in physical features of commercia] wood bucket stoves, 

particularly its too wide exhausted gap, too small combustion chamber, too 

restricted firewood feeding port, and poor stove rim design to fit pots and 

pans properly. Besides, the improved design is intended to replace the 

three-stone stoves which are ranked second in popularity among rural Thai 

users. 

After a long process of attempting to make a dual purpose stove both 

for charcoal and wood, test results have indicated that such a stove 

would greatly compromise on charcoal fuel used and would make the operation 

more difficult when using firewood. This conclusion, therefore, has led to 

the development of a separate wood burning stove and charcoal burning 

stove. 

The improved nonchimneyed wood stove model RFD-2 was previously 

illustrated in Fig. 7.2. Its physical dimensions and characteristics can 


175

(a) 

Figure 7.6. Improved charcoal stove model"RFD-l"showing (a) fixeoor 

and (c) inside of 

resistant body,(b) with grate and 

fabricated stove. 

Prov o s IF 

(b) 

(c)

(a) 

Figure 7.7 Improved charcoal stove model"RFD-l"showing (a) stove 

external ready for use, (b) and (c) sectional views showing 

different pai s of construction. 

178 

(b) 

(c)

a) Stove weight, fired clay budy only 6.9 kg. 

fully fabricated 9.8 kg. 

b) Stove height 23.5 cm. 

c) Top diameter, outside 28.0 cm. 


d) Bottom diameter, outside 25.0 cm. 


e) Vertical height from grate top to stove rim 13.5 cm. 

f) Pots accommodation, pot diameter 18-32 cm. 

g) Firing chamber capacity 3,040 cm 

h) Grate, diameter 21.0 cm. 

thickness 3.0 cm. 

weight 0.9 cm. 

hole diameter 1.6 cm. 

number of holes 37 

hole area 60 cmi 

hole area/grate area 21 % 

i) Exhausted gap (for smoke outlet) 1.0 cm. 

j) Average stove wall thickness, body only 2.0 cm. 

with insulation and bucket 5.3 cm. 

k) Primary air inlet port (4 x 12.5 cm) 50 cm 

1) Firewood feeding port (9 x 12.5 cm) 100 cmi 

Test of the performance of the RFD-2 stove conducted in the laboratory 

(based on standard testing method as described in Chapter 4) are as shown 

in Table 7.3. 

Table 7.3 Test results of improved non-chimneyed wood stove model RFD-2 

with bucket. 

Test Firewood Charcoal produced Average fuel Time to boil 

run used, at end of test, burning rate mHU% 

no. gm gm gm/mmn 

515 820 20 18.2 15 27.4 

516 810 20 18.0 15 28.8 

517 750 20 17.4 15 28.1 

601 780 30 17.0 16 28.7 

604 790 25 18.4 13 28.9 

606 740 30 18.1 11 30.4 

average 781.7 24.0 17.9 14.2 28.7 

179

From the above Table, the heat utilization efficiency of RFD-2 is 

considered high when compared with all commercial model test results 

(previously presented in Table 5.7 and in Fig. 5.3 where the HU ranged from 

14.2 - 25.9% and averaged 19.8%). The time to boil of the RFD-2 seems to 

fluctuate somewhat; the average feeding rate for each run is almost the same 

(17 - 18 gm/min). This reflects the intrinsic characteristic of wood stoves 

where duplications of actual feeding are difficult. At any rate, the 

average time to boil of 14.2 min for this stove is very satisfactory when 

considering the burning rate figure. The RFD-2 consumed firewood only 17.9 

gm/min while that of commercial models ranged from 22.6 - 35.4 gm/min and 

averaged 28.4 gm/min (See Table 5.7). This means that the RFD-2 model would 

save approximately 59% of firewood over those commercial models on the 

average, while maintaining the same average time to boil (14 minutes). 

Figs. 7.8 and 7.9 show the RFD-2 stove from the actual production by a 

group of retrained local stove makers in Roi-et Province. Since the heat 

released from burning wood inside the combustion chamber is not so intense 

as in the case of the charcoal stove, the RFD-2 model can be produced either 

with or without a bucket and insulation restraint outside. This option shall 

be decided by consumers according to their ability to pay, preference for 

a neat appearance, together with ease of cleaning. The performance of RFD-2 

of both options is the same within 45 min of operation under the standard 

test. 

D. IMPROVED CHIMNEYED WOOD STOVE 

The second type of wood stove developed is the chimneyed wood stove. 

However, only three commercial models exist with one pothole as discussed 

in Chapter 5 and illustrated in Annex IlI. Even though the stove is not 

popular and finds very limited use in rural Thailand, it could compete 

with the charcoal stove in certain applications if it could be developed to 

attain the efficiency level of up to 20 - 25%. Recalling that heat 

utilization efficiency (HU) of the improved charcoal stove is 32% and the 

maximum efficiency in conversion of wood to charcoal is 60% (see report of 

charcoal improvement component), the absolute efficiency of the charcoal 

stove as calculated directly from wood raw material, therefore, is equal to 

19.2%. 

The development of the one pothole chimneyed wood stove has faced 

problems; namely, a) fitting of various sizes of pots and pans is not 

possible b) directing the flame toward the pots' bottom and around their 

side walI is very difficult. Too much draft and improper baffling will 

direct most of the flame toward the flue gas exit hole. On the other hand, 

too week a draft and too restricted a baffliLig will cause the smoke to come 

out from the firewood feeding port. 

A compromise was made on the above problems. Designs and various 

modifications were then made and tested. The prototype selected is shcwn in 

Fig. 7.3 and 7.10. Physical dimensions and characteristics are as follows: 

180

(a) 

Figure 7.8 Improved nonchimneyed wood stove model"RFD-2" 

(a) fire-resistant body with grate (b) fabricated model 

without bucket and (c) Sectional view showing parts of 

construction. 

181 

(b) 

(c)

Figure 7.9 Improved nonchimneyed wood stove model"RFD-2"showing : 

.(a) and (b) fire resistant stove fabricated model with 

bucket (c) sectional view showing parts of construction. 

182 

(a) 

(b) 

(c)

-II 

Figure 7.10 Prototype of developed chimneyed wood stove 

showing different parts of construction. 

183

a) Stove weight 7.9 kg. 

b) Stove height 23 cm. 

c) Pot hole diameter (fit best only one size) 24 cm. 

d) Firing chamber capacity 4,400 cm! 

e) Grate, diameter 23 cm. 

hole diameter 2 cm. 


hole area 60 cm? 

f) Grate-to-pot distance (pot #24) 13.5 cm. 

g) Average stove wall thickness 3.5 cm. 

h) Primary air port 50 cm 

i) Firewood feeding port (8 x 15 cm.) 120 cm 

j) Flue gas outlet hole (4 x 10 cm.) 44 cm 

k) Baffle, half-ringed length 30 cm. 

flue gas trough, height x width 3 x 1.5 cm. 

1) Chimney, diameter 10 cm. 

height 2.2 m. 

m) Adjustable external damper at lower end of chimney below the flue 

gas exit hole level. 

Test results of an improved chimneyed wood stove prototype are shown 

in Table 7.4. 

Table 7.4 Performance of the prototype improved chimneyed wood stove 

Firewood Rnn.burning Charcoal produced Average rate,H% fuel Time to boil 

Run no. use, gm at end of test, gm gm/min min 

494 1,025 25 20.1 21 19.6 

495 970 40 19.4 20 18.5 

496 950 20 18.6 21 18.5 

499 1,080 20 21.6 20 19.0 

503 1,130 20 21.3 23 17.3 

505 1,110 30 21.8 21 21.8 

average 1,044 25.8 20.6 21 19.1 

Prev2Qo opjz 

185

Test results from Table 7.4 indicate that 11Uincreased by approximately 

4.6% over the average existing models shown in Table 5.8, (that is, from 14.5 

to 19.1%). Time to boil increased from 17.7 to 21 minutes on the average. 

The major contribution of this prototype is that the firewood use is 

considerably less than the commercial models; i.e. 1,044 gm versus 1,583 gm 

or 34% less on the average. 

Since the original aim was to raise the efficiency of this chimneyed 

wood stove to 20 - 25% while maintaining at least the same time to boil, this 

prototype stove still has not met with requirements. Therefore, this stove 

should receive more improvement in the future before trial promotion or 

commission of the production. 

E. IMPROVED NON-CHIMNEYED RICE HUSK STOVE 

The nonchimneyed rice husk stove from Khao-I-Dang refugee camp (also called 

the "Meechai stove") is quite unique in its design and operating efficiency. 

Therefore, only a little improvement and modification need to be done. 

Possible modifications include the material of construction, air inlet hole 

size and number, the inner cylinder height and exhausted flue gas area, and 

the outer cone insulation. The final design has the following features: 

a) Outer cone, mild steel gauge 0.70 mm. 

upper diameter 45 cm. 

lower diameter 10 cm. 

cone angle 60 deg. 

vertical height 30.5 cm. 

b) Air inlet hole, diameter 0.9 cm. 


c) Inner cylinder, diameter 21 cm. 

height 19 cm. 

exhausted area 3(3 x 13 cm) 117 cm? 

d) Fuel flow, gap 2 cm. 

gap area 163 cm? 

f) Outer cone insulation thickness 0.5 cm. 

This improved model has the heat utilization efficiency of 19 - 20% and 

a time to boil of 11 - 13 minutes under standard tests. Rice husk used for 

one test (approximately 40 - 45 min operation) is 1.7 - 1.8 kg at 10 - 13% 

moisture content. The insulation of the outside cone with rice husk ash-clay 

mixture, eyen though offering only 1 - 2% increase in HU over the uninsulated 

one, has greatly helped in keeping the cone metal from repeated extreme heat 

exposure and rust. In so doing, however, the flow friction (the husk on 

clay mixture surface) is also increased. To correct it, the rice husk 

ash-clay mixture insulating surface must be made as smooth as possible to 

avoid rice husk sticking at the flow gap. Future development to smooth this 

186

surface should be tried, particularly with cheap glazing material such as a 

salt solution. The operation of this stove is only suitable for a wellventilated 

area such as around the yard. A container to receive hot rice 

husk ash from the ash port is necessary. In case of windy conditions, the 

stove will not operate well unless a shield is improvised. 

Fig. 7.11 shows part of construction and operation of this stove. 

F. IMPROVED CHIMNEYED RICE HUSK STOVE MODEL "RFD-3" 

The design of the RFD-3 chimneyed rice husk (and other residues of 

similar form) stove has the purpose of correcting the following weaknesses of 

commercial models: a) stove and chimney cracking because of an intense heat 

and flame generated in both cement and fired-clay constructions, b) poor 

conversion efficiency due to lack of baffling, too large flue gas exit hole 

and too far a distance from combustion zone to the pot bottom, c) too large 

a pot hole diameter so that the common family pot size (#22 - 36) cannot be 

used, d) weight of models (most are too heavy to be moved by two persons), 

and e) frequency of fire attendance during operations of some fuel efficient 

models. 

The development of the RFD-3 model has resulted in the design of physical 

structures and characteristics as follows: 

a) Stove weight, stove body only 68 kg. 

with insulation 75 kg. 

b) Stove height 33 cm. 

c) Pot hole diameter, no insulation 28 cm. 

d) Pot accommodation 22-32 cm. 

(only one size of pot has to be decided by users prior 

to insulation lining of the stove) 

e) Firing chamber capacity, no insulation 14,800 cm? 

with insulation for 24 cm pot 10,000 cm? 

f) Iron grate, slope 43 deg. 

rod diameter 6 mm. 

finished length 36 cm. 

g) Air inlet area 450 cm 

h) Ash removal port 60 cm 

i) Flue gas exit hole uninsulated 50 cm 

insulated 32 cm 

j) Base to pot distance for pot #24 19 cm. 

187

a b 

PrviOUS Paz 189 

c 

Figure 7.11 

Nonchimneyed rice husk stove, the 

"Improved Meechai" model showing: a) 

an insulated outsidc -one sitting on 

the steel ring with three wooden legs, 

the inside cylinder with three 

exhausted gaps for flue yas exit, and 

the ash removal port at bottom of the 

cone, b) the stove's top view before 

flue loading and c) the stove during 

operation.

k) Average insulation thickness 1.2 cm. 

1) Chimney, inside diameter 10 cm. 

total height 220-240 cm. 

length of refractory bottom portion 50 cm. 

Tests of the performance of the RFD-3 model (based on the standard method 

previously described) are as shown in Table 7.5. 

Table 7.5 Test results of improved chimneyed rice husk stove model RFD-3 

Rice husk Average burning Time to boil HU % Remarks 

use, gm rate, gm/min min 

142 2,830 61.5 16 10.0 Operated at the 

143 2,930 65.1 15 10.5 chimney height 

146 3,300 68.8 18 9.4 of 220 cm. 

151 3,310 66.2 20 11.6 

152 3,330 62.8 23 10.7 

average 3,140 64.9 18.4 10.4 

From Table 7.5 the heat utilization efficiency of the RFD-3 reached an 

average of 10.4%. This increase was quite considerable when compared with 

the original commercial models in Table 5.9 (where HU was only 4.2 - 7.1%). 

The time to boil for commercial stoves without any modifications ranged from 

18.5 - 27.0 minutes and averaged 22.4 minutes. The RFD-3 performance in this 

respect (average 18.4 min) is quite satisfactory. The fuel consumption of 

the commercial models ranging from 65.6 - 160.7 gm/min (with a mean of 

108.0 gm/min) was considerably higher than the RFD-3 stove which consumes 

only 64.9 gm/min. 

Regarding the stove cracking problem, the inside insulation lining using 

an inexpensive rice husk ash-clay mixture has proven to be very effective 

and also serves the purpose of fitting a particular size of pot to the stove 

well. This insulation application (including some repairs later) should be 

done by users, however. 

The reception of the chimneyed rice husk stove in certain areas of 

Central and Northeastern Thailand is, at present, quite good though still 

not as popular as charcoal and wood stoves. Based on trial promotions, many 

groups of village people seem to accept the RFD-3 readily and claim that 

its construction cost of 200 baht (excluding the chimney) is much cheaper 

than the price of commercial models. 

Fig. 7.12 shows the RFD-3 improved chimneyed rice husk stove from actual 

production by one rice husk stove manufacturer at Rangsit, Phatumtani Province. 

. .. . " 191

P9 0 

Figure 7.12 

re.,o s 

a b 

Improved rice husk stove with chimney, the "RFD-3" model: 

a) an example of installation during a demonstration with 

inside insulation for 24 cm pot diameter, two portions of 

chimney, a refractory at bottom and an ordinary drain pipe 

at top; b) cement cast body with uninsulated firing chamber, 

flue gas exit hole and tunnel, sloping iron-grate and ash 

removal port under; c) side view with sleeves and hole to 

reduce its weight. 

193

Chapter 8 

Improved Stove Designs and Production 

i 7(

IMPROVED STOVE DESIGNS AND PRODUCTION 

The design and construction of a cooking stove are critical. Factors 

that influence stove performance must be fully recognized. In producing a 

stove, therefore, the technical drawings, the construction instructions and 

the methods for mass production should be closely followed. 

A. TECHNICAL DRAWINGS OF IMPROVED STOVES 

Figs. 8.1 - 8.4 are the drawings of the 4 improved stove models 

developed within the framework of this study. They are the charcoal bucket 

stove, the non-Thimney wood stove, the non-chimney rice husk stove, and the 

chimney rice husk .tove. 

B. CONSTRUCTION 7NSTRUCTIONS 

In producing efficient cooking stoves (which will be used daily for at 

least 1,000 hours a year) long-term service and durability must be taken into 

account. In order to construct such a stove, the clay body must be chosen 

carefully, formed properly and dried and fired under the correct conditions. 

Further, the grate, the bucket, and the insulation must be fabricated and put 

together correctly. And, finally, the stove must be inspected for quality 

control at various stages in its production. 

Clay Material for Pottery Lined Stoves 

A refractory clay body must be used for cooking stove production since 

the operating temperature (particularly of the charcoal stove) can reach 

1,000 - 1,200 0 C. The project investigated a number of clay bodies and found 

a refractory clay body very suitable for charcoal and wood stove production 

in the Panomprai district, province of Roi-et. Local artisans have been 

using this kind of clay for limited wood stove production for at least one 

generation. The dark brown sedimentary clay from the central lowlands that 

is widely used for stove and pottery production is unfortunately not 

refractory. A stove made from this kind of material will normally crack 

the first or second time it is used because of thermal shock. Further 

operation will cause further degradation. Refractory clay bodies require 

a high alumina content as well as some amount of iron oxide to facilitate 

a lower firing temperature. Silica, a major component of the clay body that 

gives strength to the final fired-product, must also be present in the proper 

proportion to the alumina & iron oxide. Weight loss after firing indicates 

the presence of organic or humus matter in the clay body. (The humus matter 

creates the porosity necessary in the final product thac improves the stove's 

insulating properties and makes it light weight.) However, too much organic 

matter will greatly reduce plasticity and the handling strength of the wet 

19b

clay during forming. Table 8.1 shows compositions and fire-resistant 

properties of some local clay materials used for stove and pottery 

manufacturing. 

Clay Preparation 

Since the project mainly used clay for improved stove production from 

the source at Roi-et, the following discussion covers only this clay type; 

however, tie information is applicable to the preparation of clay for making 

stoves in other situations, given that a properly refractory clay body has 

been found. 

The dried clay raw material was soaked with water in a pit and left 

standing fo. at least 12 hours. After 12 hutirs the wet clay was separated 

into two parts (2 and J). Two-thirds would be used later as a main mix. 

One-third was further mixed with an equal volume of fresh rice husk and hand 

formed into biscuits. After air drying, these biscuits were open fired with 

fuelwood for 6-12 hours until all pieces were evenly baked. The baked 

biscuits were pounded into small granules (with the bigger size not more than 

1 mm in diameter). The prepared substance (or so-called "caking powder") was 

added to the main mix (two-thirds of the original clay) previously set aside. 

These two components were then mixed as thoroughly as possible with enough 

water added to ensure that the wet clay mixture would retain its shape during 

forming and/or throwing. 

Forming the Stove from Wet Clay 

In practice, forming a stove from clay is carried out using three 

different methods as follows: 

Using of potter'L wheel and external mold 

Using a potter's wheel with an external mold is the most popular method 

used in bucket stove making, particularly in !Xntral Thailand in areas such 

as Rajaburi, Nakorn Pathom, Pathumthani, and Chachoengsao. The clay is quite 

soft and can be formed easily on the potter's wheel with an external mold 

acting as a restraint shell. This method, at present, gives the highest 

production rate but yields poor accuracy of the critical inside dimensions 

of the stove. Therefore, it is not a suitable method for improved stove 

production. 

Using of wooden spatter and hand foming 

The wooden spatter and hand forming method is still practiced by Panomprai 

stove makers. By hand, the potters form the hard clay into the ihape of.the 

stove desired. Thereafter, a wooden spatter is used for beating around the 

outer surface to ensure final integrity and strength. This method is 

considered a very poor method for commercial Troduction since the production 

rate is low and there is poor control of the stove's dimensions. 

198

Table 8.1 

Compositions and fired resistant property of some local clay materials used 

for stove and pottery productions 

Clay source and/or Major clay composition % Fire resistance 

mixture Loss on SiO 2 Al203 Fe203 Others 0C 

ignition 

1. Pano,,prai Roi-et, an original 9.8 61.5 24.5 2.4 1.8 1632 

raw material sample 

2. Panomprai Roi-et. a final 8.6 61.7 23.8 2.6 3.3 1621 

mixture sample prior to 

throwing 

3. Banmor Mahasarakarm, a river 6.2 77.4 11.9 2.0 2.5 1501 

bed sample 

4. Pakred Nondhaburi, a dark 8.9 59.0 19.2 6.9 6.0 na 

brown central lowland sample 

5. Pakplee Prachinburi. a white 12.3 56.1 25.9 3.0 2.7 na 

clay or kaolin sample 

Source: Clay samples no. 1-3 wece analyzed and tested by Department of Science Service, Ministry of 

Science Technology and Energy. 

Data on compositions of clay samples no. 4 and 5 were obtained from Industrial Service 

Division, Department of Industrial Promotion, Ministry of Industry.

Using the internal mold in cooperation with a potter's'wheel and spatter 

Using an internal mold, a potter's wheel and spatter was a method 

developed by project personnel as a combined technique to improve the above 

two methods and control the stove's internal dimensions, integrity, and 

provide a reasonable production rate. A detailed production process is 

shown in the following photographs (Figs. 8.5 - 8.8). After the Pranomprai 

stove makers were trained briefly in this production method, the production 

rate, precision and stove quality greatly improved. Using this technique 

more than 3,500 charccal and wood pottery liner stoves were produced in 

three months (for the project's initial dissemination) employing four molds 

and eight workers from four families. 

Stove Drying 

Stoves newly formed from wet clay require shaded air drying for several 

days (approximately 3 - 5 days in the dry season and 10 - 12 days in the 

rainy season). During this drying stage, the clay stove form will shrink. 

Therefore, care should be taken to ensure uniform and gradual drying to avoid 

stove distortion and/or cracking. When the clay stove form has become 

"leather hard" it can be placed in the sun for a final i - 2 days of drying. 

Stove Firing 

After stoves have been properly dried in both stages, a quality check 

must be performed. Stoves with severe defects such as cracking, distortion, 

and dimension discrepancies (due to excessive shrinkage) will be rejected. 

(The clay can be re-wet for r6jse as raw material in another batch.) Firing 

of stoves is carried out in an old-fashioned manner. Local stove makers 

employ an open-firing technique. Open-firing requires that a level ground 

area of 8 - 10 sq meters be laid with dried rice straw approximaterly 3 - 4 cm 

thick. Dried firewood sticks (approximately diameter 3 - 4 cm) are placed 

horizontally as the first layer on the straw bed. Then the second layer of 

firewood (slightly larger in size, approximately 5 - 10 cm) is horizontally 

stacked on top, with the length perpendicular to each other. Altogether, 

3 - 5 layers of firewood are required to make the pile approximately 40 cm 

high. The amount of firewood required for this size of a pile is 700-800 kg 

(at 12 - 15% wood moisture content). This pile will accommodate 100 stoves 

per firing. 

Stoves to be fired are carefully placed on the firewood pile as close 

to each other as nossible in one single layer. The rice straw around the 

pile is then ignite.- After the first layer of firewood starts catching 

fire, the operator will throw rice straw on top and around the pile, As the 

straw keeps on burning it will release heat and provide insulation to the 

top and sides of the stove pile. The firewood inside will continue burning 

for approximately 2 - 4 hours. Then the pile will be left alone for self 

curing and cooling for 12 - 15 hours more. Stoves are normally unloaded 

from the pile the following day. 

200

Figure T.ec ica) aing of te Io 

U- 

L sJr4LY4:4 

S---..I 

K'~~~S 

I iiI . . . . . 

-A i~IT 

,/' U,.,, ': 1 -'"... r _ . . 2- 

0 

'- - -....... - 4 

Figure 8.1 Technical Drawing of the Improved Charcoal Stove

\Ix FL 1 '1-, 

4LI7I7f-4771 

* . -- 

SegK SODY VaW) A '4t 

. 

0 • 

000 0 

00u0t 4444 

I * 

I--..'-4-- 

... . 

- iwF-bi 

GRA'rE S'"I 

8.2 1 ISO 11fm11S 

Figure 8.2 Technical Drawing of the Improved Wood Stove

-a0G 0----* - - 

&. 

-------- , -. 

_ _ _ _/ 

- . I I, 

-itl 

lioi i1 

*,.1 

Figure 8.3 Technical Drawing of Improved Rice Husk Non-chimney Stove 

RK FOeS1 .- Th oo 

.en-

41 

. .. 

1Iihrn:tR,-', - 

K,, --gnu4 

. . eI 

,1,4 i__O/ - 

Figure 8.4 Technical Drawing of Improved Rice Husk Stove with Chimney

Figure 8.5 Preparation of biscuits and firing to be later used 

for clay mixture. 

Figure 8.6 Production of charcoal stove on the potter's wheel 

using the internal mold. 

205

Figure 8.7 Disassembling of the internal mold from a newly made 

charcoal stove. 

Figure 8.8 Improved charcoal and wood stoves after finished 

firing and ready for further fabrication. 

206 

k.

Stove's Quality Inspection 

Even when firing is carried out by experienced local stove makers, some 

defects may occur due to non-uniform heat and cooling at certain spots in 

the pile. The final inspection will reject the stoves that are underfired, 

cracked and distorted. Normally, however, our results show a rejection of 

less than 7%. 

Stove's Grate Making 

Pottery liner stoves, as well as charcoal wood stoves, need grates for 

efficient combustion. However, the design for each is slightly different. 

See their detailed dimensions in Figs. 8.1, 8.2, 8.9. The clay composition used 

for making the grate is different from the clay mixture used to make the 

stove body. The rice husk ash content is higher in the grate body to reduce 

shrinkage during production and to enable the grate to withstand high thermal 

stress during use. 

The normal composition of a thick charcoal grate is approximately 2-parts 

clay to 3-parts refined white rice husk ash by volume. The grate is handformed 

in a ringed-mold and hand-punched by a tapered tube with the help of 

a hole template. After air drying for approximately 15 days, this type of 

grate need not be fired since it becomes cured during use and has enough 

initial strength to withstand a charcoal load. 

A wood stove grate, on the other hand, is thinner and larger in diameter. 

Therefore, prior to use, it must be fired first to become strong. In 

addition, a wood stove grate is made with a rougher clay body 1-part clay 

body and 3 parts black rice husk ash (which has not been refined and/or 

sieved). 

Stove Bucket Making 

Long term servicability and heat conservation within the stove rely 

heavily on the outside bucket. A good bucket is designed to fit the stove 

properly, so that the gap for packing the insulation between the stove and 

the bucket is 1.5-2.0 cm around the tapered wall. The bucket height will be 

0.5 cm shorter than that of the stove to facilitate insulation filling and 

sealing with cement. A standard galvanized iron sheet of 0.3 mm gauge is 

considered the suitable size for the prototype stove. This material can 

withstand the alkalinity of rice husk ash insulating material reasonably 

weli; it can withstand external rusting due to moisture and other factors. 

A handle is an essential part of the bucket and must be able to withstand 

the normal stove weight of 10 - 12 kg in long-term service. A good quality 

bucket can be ordered in quantity (and therefore at less cost) from a water 

bucket manufacturing plant. 

207

35-40 MM 

Figure 8.9 Grate hole design for charcoal stove hole 

6 

170 

diameter 1.3 cm.,with 61 holes in 5 shells 

around the center hole. 

208

Stove Fabrication 

Essentially, pottery lined stoves (wood and charcoal) consist of four 

separate components as follows: 

" The fired clay body; 

" The grate; 

* The bucket; and 

* The refractory and insulation linings. 

The composition of material for the interior refractory lining is 5 - 6 

parts common rice husk ash and one-part clay. That for exterior insulation 

lining is 12-parts ash and 1-part clay. Both must be thoroughly mixed. 

The fabrication is completed by first pouring the insulati.ca mix into 

the bucket bottom (about 1.5 cm). The stove body is then positioned inside 

the bucket. More insulation mix is added to the gap and then is tightly 

packed inside the gap between the stove body and the bucket. The stove's 

top rim and the edge around the air inlet door are then sealed off-by cement 

mortar (3 parts fine sand and 1 part Portland cement). The grate is then 

positioned and fixed with refractory mix inside the stove body in such a way 

that the bottom edge of the grate is in line with the upper rim of the air 

inlet door. Finally, the refractory mix is lined around the combustion chamber 

approximately 1 cm thick to seql the edge between the grate and the stove 

body. The whole stove is thun aiL-dried for at least 24 hours before use to 

avoid cracking of the refractory lining. 

C. A MASS PRODUCTION SCHEME TO MAKE CHARCOAL AND 

WOOD STOVES USING THE HYDRAULIC PRESS 

In the section on "Forming the Stove From Wet Clay" three forming methods 

were discussed. However, these methods cannot meet the stove production 

criteria of high production rate, precision of internal and external stove 

dimensions, and high uniform forming pressure of hard clay to withstand high 

thermal stresses. In order to meet all three requirements, it is envisaged 

that a hydraulic press with an internal mold and an external mold would 

provide a better method for long-term commercial production. The need for 

this kind of simple equipment for local production cannot be overemphasized 

if the "improved stove promotion program" hopes to see the quick replacement 

of 5 - 6 million poor charcoal and wood stoves throughout rural Thailand. 

The prototype of such a hydraulic press in forming the clay bucket 

(includif.g molds) has been designed and individual parts have been made. 

Fabrication and testing of this machine are underway at the present tf-e. 

It is hoped that this device will work out well and out-perform those stove 

manufacturing techniques presently employed in Thailand. A detailed sketch 

of the hydraulic press for stove molding is shown in Fig. 8.10. 

209

20 

Figure 8.10 100-ton Hydraulic Automatic Press- 

Machine for Charcoal and Wood Stove. SCALE 1-5 

210 

B.SRISOM 

JANUARY 84

Chapter 9 

Improved Stove Promotion

IMPROVED STOVE PROMOTION 

Laboratory research and development df highly efficient biomass cooking 

stoves were carried out for approximately 2 years. As a result, four types 

of improved biomass cooking stoves were proposed for trial promotion. They 

were the: charcoal bucket stove, the wood stove without a chimney, and the 

rice husk stove with and without a ch:nney. The four improved types gave 

satisfactory performance. Tneir absolute efficiencies increased approximately 

5 - 7% on the average. Furthermore, performance tests on durability (long 

service life), ease of opetation (easy to start up the fire and continuously 

give high heat output with equal or little attendance), accommodation of 

various pot sizes (one stove fits pot diameter from 16 to 32 cm), and 

portability (light weight) were satisfactory. Only the wood stove with a 

chimney requires further improvement of efficiency and to accommodate a 

variety of pot s:izes. 

Any problems that arise during stove development can usually be solved 

in the 'aboratory. However, problems dealing with the introduction of the 

newly developed stoves to users need to be solved in the field. Stove 

promotion is a most important project task. The work involved in research 

and development will have been wasted if improved models are not accepted 

by users. Hence,the promotion of improved stoves is one of the main 

concerns of this project. 

This chapter presents some activities and field work involved in 

introducing improved stoves to rural families. 

A. OVERALL TARGET OF STOVE PROMOTION 

The population of Thailand is approximately 50 million. The avcrage 

number persons in a family is 6 persons. Approximately 80% of Thai families 

live in rural areas. Thus, there are roughly 6 million biomass cooking stoves 

used by rural families. This presumes that each family has only one cooking 

scove. (In fact, a large number of rural families have 2 - 3 stoves in their 

possession). The main problem of promotion then becomes how to get all of the 

stoves replaced within a certain time frame. If Thailand were to replace 

all 6 million Inefficient stoves within say, 5 years, approximately 1.25 

million improved stoves must be produced. The activity involved in 

producing this many improved stoves is tremendous. It is not possible for 

a government agency to carry on such a heavy task alone. Stove manufacturers 

throughout the country must be involved in the production process. However, 

to begin this implementation program, the government must initiate and 

stimulate stove promotion activities so that stove replacement time will be 

shortened. 

This project had only 6 months to begin the campaign. Stove promotion 

and training schedules have been established. There are two projects under 

the same component leader: Charcoal Improvement and Stove Improvement. 

, ... . . 2 13

Therefore, both projects have been combined into one promotional campaign. 

Each promotion activity generally takes 5 - 10 days. Improved stoves are 

introduced during the first 1 - 2 days and charcoal production is demonstrated 

during the remaining time. The subjects present in the promotion activity 

depend on the level of education and the capability of participants. For 

representatives of government agencies and rural development associations, 

promotion activity elaborates both theoretical and practical details (since 

this group is more knowledgeable and is directly responsible for carrying out 

this development program in rural areas). Another group of participants 

consists of people who live in the villages. Hence, the promotion activity 

is less technical, and emphasizes only the practical, specific features of 

good stoves and their proper care. A prepared time-schedule for promotion 

activities is presented below: 

1. The first trial promotion of the charcoal and stove improvement projects. 

Place: Regional Energy and Technology Center for Rural 

Development 

Muang District, Mahasarakarm,.Northeastern 

Date: 9 - 16 December 1983 

2. Technology of charcoal production and introduction of developed stove-the 

first official training course for government and rural development 

agencies. 

Place: Charcoal Research Center 

Muang District, Saraburi, Central 

Date: 9 - 20 January 1984 

3. Improved production of charcoal and introduction of developed stoves to 

rural families--a training course for villagers and officials of the 

Mobile Military Development Unit. 

Place: Mobile Military Development Unit #32 

Pannanikorm District, Sakolnakorn, Northeastern 

Date: 1 - 11 February 1984 

4. Improved ?roductionof charcoal and introduction of developed stoves to 

rural families--a training course for villagers. 

Place: Regional Energy and Technology Center for Rural 

Development 

Muang District, Pitsanulok, Northern 

Date: 5 - 9 March 1984 

5. Technology of charcoal production and introduction of developed stoves 

to rural families--the second official training course for Government 

and Rural Development agencies. 



Date: 13 - 23 March 1984 

214

6. Improved produntion of charcoal and introduction of developed stoves 

to rural families--a trainig course for villagers. 

Place: Khao Hin Sorn 

Educational Development Center, 

(under H.M. the King's direction) 

Panomsarakarm District, Chachoengsoa 

Date: 16 - 20 April 1984 

7. Improved production of charcoa:. and introduction of developed stoves to 

rural families--a training course for villagers. 

Place: Ban Thatoom Secondary School 

Muang District, Maharasakarm, Northeastern 

Date: 30 April - 4 May 1984 

8. Technology of charcoal production and introduction of developed stoves 

to rural families--the third official training course for the Mobile 

Military Development Unit. 



Date: 14 - 25 May 1984 

9. Improved production of charcoal and introduction 

to 

of 

rural 

developed 

families--a 


training course at the Mobile Military Development 

Unit. 

Place: Mobile Military Development Unit #22 

Poa District, Nan, Northern 

Date: 3 - 10 June 1984 

To achieve this project goal, it must be 

of 

emphasized 

newly developed 

that the 

stoves 

promotion 

is not just to distribute 

variety 

the stoves 

of aspects 

to users. 

must 

A 

be considered. For 

fabrication, 

example, stove 

repair 

production, 

and maintenance, 


and criteria 

from 

for 

the 

selection 

markets 

of 

should 

good 

be 

stoves 

included in promotional 

of this field 

workshops. 

work is, 

The 

therefore, 

intention 

to educate users on 

well. 

the above 

In fact, 

subjects 

trainees 

as 

are required to participate 

They 

in 

install 

stove fabrication. 

the stove grate, prepare insulating 

refractory 

materials, 

part, 

line the 

fill 

inside 

the stove bucket with insulation 

rim. Overall 

and seal 

promotional 

the stove 

activities are summarized in the subsequent section. 

B. CREATION OF PUBLIC AWARENESS 

In order to distribute 1.25 million improved stoves to rural families 

throughout the country (in additioi, to promotional activities carried out 

by this project), the government must step in to initiate various kinds of 

campaigns such as press conferences, radio interviews, distribution of 

leaflets and posters, etc. 

The first introduction of cooking stoves (and related subjects) to the 

public was conducted by the National Energy Authority on 3 - 4 August 1983. 

Cooperating closely with the Stove Improvement Project, the meeting included 

215

a seminar, demonstration, and exhibition of cooking stoves. The participants 

consisted of representatives from government institutions such as universities, 

the Agricultural Department, the Rural Development Department, the Welfare 

and the private sector such as 

Department, the Ministry of Education, etc., 

the Population and Social Development Assoication, VITA company, Appropriate 

Technology Association, and a number of stove manufacturers, etc. The purpose 

of this campaign was to bring together the researchers, users, and 

manufacturers to join in a panel discussion in order to share points of view 

on several aspects of the project such as standard methods of stove testing, 

special features of highly efficient stoves, experience in stove manufacturing, 

marketing, and quality control. 

Another promotional effort was the press conference on newly dereloped 

biomass cooking stoves which was held in February 1984 at the Ministry of 

Science and Technology. Representatives from radio and television stations 

the meeting. 

and representatives from various newspapers were invited to 

a user's guide on stove maintenance 

Leaflets, posters, T-shirts as well as 

and repairs were distributed. 

It should be emphasized that the work involved in promoting improved 

stoves to users and manufacturers is extensive and should be continued with 

the support of various government agencies. 

C. INTRODUCTION/TRAINING ON EFFICIENT STOVES 

improved stoves for local rural develoment 

The introduction/training on 

officials, school teachers, village leaders, etc. has been carried out 

The training 

following the program described in section A of this chapter. 

activities include: 

1. Instruction on the five proposed types of biomass cooking stoves on the 

fundamentals of stove design and construction (see Fig. 9.1); 

2. Efficiency test comparison between the developed stoves and the currently 

marketed stoves (see Fig. 9.2); 

3. Demonstration and trainee participation in installing the grate into the 

stove body, lining refractory material around the combustion chamber, and 

placing the insulating materials between the bucket and the stove body, etc. 

(see Fig. 9.3)/ and 

4. Distribution of the finished stoves (fabricated by traii. ;s)to those 

who have participated in building their own selected stoves (see Fig. 9.4). 

The training activities are discussed in the following section. 

216

Table 9.1 Comparison test for efficiency between developed and commercial staves in 

Mahasarakarm 

Condition Charcoal stove Nonchimneyed wood stove Chimneyed rice husk Nonchimneyed rice husk 

developed comm. I comm. 2 developed comm. developed developed 

(pranomprai) 

Fuel wt, gm 400 400 400 1,520 1,490 3,800 3,070 

Half time to boil (64'C), min 9 14 17 7 9 9 14 

Time to boil, min 17 27 27 12 14 29 22 

Water evaporated, gin 810 420 450 1,310 1,210 1,400 1,160 

Fuel remaining, gm 60 40 40 25;5701 45;330 550 1,050 

Fuel use, gmn 340 360 360 950 1,160 3,250 2,020 

Efficiency, % 31.01 20.59 21.27 24.90 19.90 9.60 13.67 

Note: 1. Charcoal remaining; wood remaining

The First Promotion Trial for the Charcoal and Stove Improvement 

Projects, 9 - 16 December 1984, Muang District, Mahasarakarm 

The purpose of this trial was to provide the trainers with experience 

in stove promotion training. There were 35 trainees, they included: 

5 Officers from the Regional Energy and Technology Center for Rural 

Development 

2 Officers from Lhe NEA Training Center 

4 Promotors and researcherl 

4 District agriculture offirs 

2 Sub-district development officers 

15 Village leaders 

2 Primary school teachers 

1 Public health reporter 

The training program consisted of the four activities described at the 

beginning of this section. The results of the comparison between the improved 

charcoal bucket stove, the improved non-chimneyed wood stove and the commercial 

ones are shown in Table 9.1. 

Thirty-two questionnaires were distributed to the trainees after the end 

of the program. The results are summarized below. 

Within this district in Mahasarakarm, the charcoal bucket stove was the 

most popular stove type. The non-chimneyed wood stove, the chimneyed wood 

stove, the non-chimneyed rice husk stove, and the chimneyed rice husk stove 

were less popular--in that order. 93% of the trainees said they knew more 

about the specific features of the highly efficient stoves as well as criteria 

for selecting good stoves after the training. 56% of the trainees increased 

their knowledge of building and designing good stoves. 84% of the trainees 

felt they had a better understanding of stove care and maintenance. However, 

only 50% of the trainees said they could transfer this training to others. 

Responding to length of training, 66% said the timing was convenient and the 

length of training was adequate. Other comments were personal that additional 

training on the method of making the.developed stoves for use was needed; more 

promotion and distribution of stove samples to other villages, more training 

should be offered to other private and government agencies as well as to 

interested outsiders; and there was a request for construction blueprints of 

the five developed stoves. 

Stove Promotion in Saraburi on 9 20 January 1984 

The stove promotion workshop in Saraburi was the first official training 

course and the opening of the Charcoal Research Center. The ceremony was 

witnessed by the following representatives: 

1 Representative from the National Energy Administration 

4 Chief engineers and officers from USAID office, Thailand 

2 Representatives from Food and Agriculture Organization, Asia and Pacific 

Region 

218

2 Representatives from the Forestry Department 

1 Representative from Kasetsart University 

1 Chief of a biogas development project 

1 Chief of a renewable energy project, from the support office 

2 Representatives from the Regional Forestry Office, Saraburi 

1 Representative from the Provincial Forest Office, Saraburi 

The trainees consist of: 

5 NEA officers from the Regional Energy and Technology Center 

2 Training officers from the National Security High Command 

4 Field officers from the Community Development Department 

2 Field officers from the Family Planning and Population Development 

Association 

2 Field officers from the Land Development Department 

The formal training program was carried out as outlined in the beginning 

of this section. The charcoal stove comparison was performed and the results 

are shown in Table 9.2. 

Since this training program was devoted mainly to charcoal production, 

stove promotion was only minimally presented to participants. Only the stove 

charcoal stove comparison was demonstrated. See Table 9.2. 

No stove questionnaires were distributed 

Table 9.2 

Comparison Test for Efficiency 

between developed and commercial stoves in Saraburi 

Condition Charcoal Stove 

Developed Rangsit Cholburi Boobparam 

Fuel wt, gm 400 400 400 400 

Half time to boil (64*C), min 11 12 13 14 

Time to boil, min 17 24 27 31 

Water evaporated, gm 790 450 410 400 

Fuel remaining, gm 40 35 45 35 

Fuel use, gm 360 365 355 365 

Efficiency, % 29.16 21.40 20.48 19.73 

'219

Stove Promotion in Sakolnakorn on 1 - 11 February 1984 

The participants consisted of: 

17 Training personnel from the Mobile Military Development Unit 

5 Officers from the District Development Section 

1 Teacher from the Nonroau school 


19 Villagers 

The training program was conducted as previously described. The results 

of the stove comparison between the developed models and the commercial stoves 

are shown in Table 9.3. 

The results were obtained from 45 questionnaires, From analysis of the 

questionnaire responses, the following can be concluded. 

Non-chimneyed wood stoves made up 68% of all stoves used by the trainees 

at home. Within this region, 56% of rural families used the non-chimneyed 

type. 88% of the trainees believed that they had learned more about the 

criteria for selection of good stoves by the end.of the training. 94% of the 

trainees improved their knowledge on proper care and maintenance of stoves. 

All participants (100%) agreed that the developed stoves performed better 

than the commercial ones. 

33% of the trainees preferred the charcoal bucket stove, 32% preferred 

the non-chimnened wood stove, 19% preferred the non-chimneyed rice husk stove, 

and 16% preferred the chimneyed rice husk stove. 

At the end of trainiL.g, each participant received a stove. The 

number of stoves distributed: 43 charcoal bucket stoves, 27 non-chimneyed wood 

stoves, 4 non-chimneyed rice husk stoves, and 15 chimneyed rice husk stoves. 

Out of the total number of stove distributed, 45 stoves were given to villagers, 

2 stoves were given to a youth group from Moungkai village, and 42 stoves 

were given to the Mobile Military Development Unit. 

Stove Promotion in Pitsanulok, 5 - 9 March 1984 

The Pitsanulok training was held at the Regional Energy and Technology 

Center. There were 33 participants involved; they are: 

5 Officers and workers from the Regional Energy and Technology Center 

4 Lecturers from the Educational College and teachers from the primary 

school 

9 Sub-district senior personnel and assistants, village assistants and 

leaders of village committees 

14 Farmers and people from the region 

The results of the stove comparison between the improved model and 

the commercial stoves are shown in Table 9.4. 

220

Table 9.3 

Comparison test for efficiency between developed and commercial stoves in Sakolnakorn 

Condition Charcoal stove Nonchimneyed wood stove Chimneyed rice husk 

developed commercial developed commercial 1 commercial 2 commercial 3 developed 

Charcoal wt, gm 400 400 1,100 1,050 2,275 1,240 2,800 

Time to boil, min 22 -1 14 15 22 31 19 

Water evaporated, 

gm 640 110 1,240 1,140 950 600 1,440 

Fuel remaining, 

gm 45 25 40;2302 25;0 265;170 50;365 300 

Fuel use, gm 355 375 870 1,050 2,105 865 2,500 

Efficiency, % 29.2 14.7 12.7 

Note: i. not boil (windy on the test day) 

2. charcoal remaining; wood remaining

The results of training are summarized below. The basic information 

on the type of stoves used among the trainee's families revealed that 75% 

had: charcoal bucket stoves, 8% had non-chimneyed wood stoves ana 17% had 

chimneyed and non-chimneyed rice husk stoves. 97% of the trainees chose 

the charcoal bucket stove as their preferred model. 38% chose the non-chimneyed 

wood stove as their second preference. All trainees gained confidence in 

their knowledge of how to select good stove. 50% of the participants were 

in favor of the present desing and the other 50% preferred the new design. 

All trainees agreed that they better understood stove care and maintenance. 

This training was highly successful. The trainees showed great interest 

and cooperated well during fabrication and discussion. At the end of each 

day, trainees gathered around the training site and discussed the problems 

that had arisen during the day. All 71 participants received a developed 

stove. 

Stove Promotion in Saraburi on 13 - 23 March 1984 

The March 1984 workshop was the second official training course at the 

Charcoal Research Center in Saraburi. 

A total of 11 persons from various government agencies and private 

associations participated in the stove promotion program. These included: 

3 Training officers from Military Central Security 

2 Workers from the Family Planning and Population Development Association 

4 Workers from Community Development Department 

1 Worker from the Land Development for Agriculture Division 

1 Worker from the Thai-German Center, Welfare Department, Lopburi 

The training course was carried out according to the program previously 

mentioned. The stove comparison for efficiency is shown in Table 9.5. 

Evoluation of this training from the responses on the returned 

questionnaires can be summarized as follows: 82% of the participants used 

charcoal bucket stoves and 18% used gas stoves. All trainees (100%) said 

they had a better underscanding of the criteria for selecting a good stove. 

82% of the trainees (moderately) believed that they could transfer their 

stove knowledge to rural people. 

Stove Promotion in Chachoengsoa on 16 - 20 April 1984 

The training in Chachoengsop was set up at thu Khao Hin Sorn Educational 

Development Center under His Majesty the King's direction in Panomsarakarm 

district, Chachoengsoa Province. There were 36 participants; they included: 

6 Agricultural workers from th2 Land Development Division, Khao Hin Sorn 

Development Center 

2 Field officers from the Community Development Department, Khao Hin Sorn 

Development Center 

222

3 Field officers from the Forest Nursery Plant Center, Forestry Division 

9 Students from the Rachaburi Agricultural Institute, Rachaburi 

16 Villagers from Khao Hin Sorn region and nearby 

The results of comparison between the improved model and commercial 

stoves are shown in Table 9.6. 

At the end of the training program, 34 questionnaires were distributed 

to participants. The results are presented below. 

The charcoal bucket was the most popular types of stove. 71% of the 

participants chose it as their preference. The other choices were non-chimneyed 

wood stove--18%, non-chimneyed rice husk stove--5%, chimneyed rice husk stove- 

3%, and chimneyed wood stove--3%. 

All participants (100%) agreed that their knowledge about selecting highly 

efficient stoves had increased significantly. 977 -tated that their 

undersvanding of stove use, care, and maintenance .J also increased;41% of 

the participants have confidence in their ability to transfer their stove 

knowledge to others. In addition, many participants requested more elaborate 

details for stove making. 

At the end of training, 24 charcoal bucket stoves, 9 non-chimneyed wood 

stoves, and 4 non-chimneyed rice husk stoves were given to participants. 

Another 18 stoves were donated to the Land Development Center, the Forest 

Nursery Center and representative students from the Agricultural Institute 

for future u in stove promotion activities. 

Stove Promotion in Mahasarakarm on 30 April - 4 May 1984 

56 people participated in this training: 

2 Teachers from Ban Thatoom school 

1 Teachers from Ban Dotangarm school 

1 Teacher from Ban Napangdonhi 

2 Offi ers from the Regional Energy and Technology Center 


1 Assistant village leader 

44 Villagers 

2 Observers from the External Educational Center 

The results of the comparison between the improved stoves and the 

commercial ones are presented in Table 9.7. 

From the responses on the questionnaires, it was determined that 67% of 

the participants used charcoal bucket stoves and 29% used non-chimneyed wood 

stoves at home. 73% preferred charcoal bucket stoves while 21% preferred 

non-chimneyed woo.k stoves. 97% of the participants believed that their 

knowledge in selecting good stoves had increased, as had their ability to 

repair and maintain stoves in good condition. 50% believed that they 

could transfer this knowledge to other people. There were also many requests 

for complete instructions on how to make the stove for one's own use--starting 

223

from nothing. The training course only lets each participant place a 

pre-shaped and fired stove body into a bucket. He then places the geate, 

lines it with the refractory material, and fills it with insulating materials. 

This request is similar to other previous training course. However, the metilod 

of making stove body is rather complicated, time-consuming, and requires high 

skill; hence, this function needs to be performed by stove manufacturers. 

Instead it was suggested that the participants take the stove samples to stove 

manufacturers in their villages for trial production. 

There were altogether 137 stoves distributed at the end of training. 56 

stoves were given to participants, 81 stoves were given to Ban Thatoom school. 

The distributtA stoves included 80 charcoal bucket stoves, 50 non-chimneyed 

wood stoves, 5 non-chimneyed rice husk stoves, and 2 chimneyed wood stoves. 

Stove Promotion in Saraburi on 14 - 25 May 1984 

The May 1984 training took place at the Charcoal Research Center in 

Saraburi. There were 19 participants; they included: 

3 Military officers from the Central Security Division 

5 High-ranking military officers from the Mobile Military Development Unit 

6 Noncommissioned officers from the Mobile Military Development Unit 

5 Participants from the Regional and Voluntary Self-defense Association 

The results of the stove comparison are shown in Table 9.8. 

Questionnaire evaluation showed that 88% of the participants used charcoal 

bucket stoves and 6% used gas stoves at home. Their increased ability to 

identity and seiect highly efficient stoves was reported to be 94%. The ability 

of participants to transfer this training knowledge to other people was 50%, 

and the trainer's capability of interpretating and monitoring the stove 

training course was 72%. 

At the end of the training program, participants received 19 newly 

developed charcoal stoves. 

Improved Stove Promotion in Nan on 2 - 8 June, 1984 

This prnram was the last training course of the project. The training 

was coordinated by Colonel Dusit Menapothi, Chief of Training division, Central 

Security High Command and Special Colonel Padej Anwong, Commander of the 

Military Mobile Development Unit #22, Nan. There were 54 participants. They 

included: 

2 Training officers from the Military Mobile Development Unit #21, Uttaradit 

20 Training officers from the Military Mobile Development Unit #22, Nan 

4 Field officers from the Battalion Cavalry , Nan 

3 Workers from the external Education Center, Nan 

4 Noncommissioned officers 

21 Villagers 

224

Table 9.4 

Comparison test for efficiency between developed and commercial stoves in Pitsanulok 

Condition Charcoal stove Nonchimneyed wood stove 

Developed Commercial 1 Commercial 2 Developed Commerical 

Fuel wt, gm 400 400 400 - - 

Time to boil, min 241 (17) _2 24 11 13 

Water evaporated, gm * 720 460 540 1,340 1,240 

Fuel remaining, gm 30 20 25 20 15 

Fuel use, gm 370 380 375 890 1,160 

Efficiency, % 29.5 22.1 24.5 26.8 19.1 

Note: 1. The value is somewhat higher due to trainees' lack of skill in lighting the fuel. The same test 

was repeated on the next day and a new time to boil was quoted in the parenthesis. 

2. Not boiling.

01 

Table 9.5 

Comparison test for efficiency between developed and commercial stoves in Saraburi 

Condition Charcoal stove Non-chimneyed wood stove 

Developed Commercial Developed Commercial 1 Commercial 2 

Fuel wt, gm 400 400 - _ 

Time to boil, min 19 23 20 27 18 

Water evaporated, gm 610 510 1,310 1,210 1,000 


Fuel use, gm 360 370 1,030 1,170 1,020 

Efficiency, % 28.4 24.5 23.8 19.7 19.2

Table 9.6 

Comparison test for efficiency between developed and commercial stoves in Chachoengsoa 

Condition Charcoal Stove Nonchimneyed Wood Stove 

Developed Commercial Developed Commercial 1 Commercial 2 

Fuel wt, gm 400 400 

Time to boil, min 17 32 17 16 15 

Water evaporated, gm 620 410 1,130 1,100 1,250 


Fuel use, gm 360 355 820 920 1,210 

, Efficiency, % 26.33 21.64 24.86 21.75 18.0 

* Very windy condition during the test day 

- 

- 

-

Table 9.7 

Comparison test for efficiency between developed and commercial stoves in Mahasarakarm 


Developed Commercial 1 Commercial 2 Developed Commercial 1 Commercial 2 

Fuel wt, gm 400 400 400 1,390 1,410 1,570 

Time to boil, min 24 26 _1 14 19 19 

Water evaporated, gm 560 480 60 1,260 960 1,140 

Fuel remaining, gm 65 65 110 505 720 635 

Fuel use, gm 335 335 290 885 690 935 

Efficiency, % 31.14 28.79 22.15 25.06 23.97 21.28

The results of the comparison between the improved models and the 

commercial stoves are shown in Table 9.9. 

54 questionnaires were returned. The. result are summarized below. 

The most popular type of biomass cooking stover trainees was the charcoal 

bucket stove; used them at home 68%. The next popular type was the nonchimneyed 

wood stove accounting for 29%, and the chfmneyed rice husk stove 

3% ccounting for all participants received a stove. 

At the end of the training, 54 developed stoves were distributed. 

D. INTRODUCTION AND DISTRIBUTION OF SAMPLE STOVE 

TO HOUSEHOLD USERS 

The trial promotion and training course in improved stoves should 

include free distribution of stove samples to rural villagers under the 

condition that the promotors follow up and record the results. Thus, any 

problems that may arise during the application of the new models can be 

addressed and improvements made. Free distribution of sample stoves must be 

supported by the government, particularly in the trial promotion and monotoring 

phases. 

E. ORGANIZATION OF STOVE MANUFACTURERS TO PRODUCE 

IMPROVED DESIGN STOVES 

Introduction to manufacturers of the improved stoves is a very difficult 

task because of iack of concern and cooperation among local stove manufacturers. 

These problems are believed to exist because they: 

* Have little credibility with the government agency; 

w Believe that the stoves they are making are best (due to lack of 

scientific knowledge); 

* Believe that the stove making profession is doomed because of strong 

competition from gas stoves and their LPG fuel government subsidies. 

a Believe that Thailand is running out of wood and charcoal. Many state 

that riiey will give up stove manufacturing when there is no more wood. 

Hence, government agencies should focus on educating local stove 

manufacturers to better understand Thailand's precious, indigenous and 

reproducible source of unargy--wood--and t)y providing them with guidance and 

useful scientific knowledge on improved stove technology. This can be 

achieved by the following government efforts: 

1. Publication and distribution of documents describing the important 

features of good stoves. 

229

D 

Table 9.8 

Comparison test for efficiency between developed and commerical stoves in Saraburi 



Fuel wt, gm 400 400 400 1,670 1,710 1,500 

Time to boil, min 20 21 26 14 22 i6 

Water evaporated, gm 360 345 360. 950 710 1,020 

Fuel remaining, gm 40 55 40 40;7201 55;1,000 35;480 

Fuel use, gm 730 550 440 1,360 920 1,260 

Efficiency, Z 30.32 27.50 23.52 26.23 28.33 

Note: 1. charcoal remaining #; wood remaining 

22.83

Table 9.9 

Comparison test for efficiency between developed and commercial stoves in Nan 

Condition Charcoal stove Non-chimneyed wood stove 


Fuel wt, gm 400 400 400 

1 

1,440 1,460 1,440 

Time to boil, min - 

- 

- 

Water evaporated, gm 600 410 - 1,280 1,060 1,020 

Fuel remaining, gin 40 35 - 40;300 60;190 50;215 

Fuel use, gm 360 365 - 1,140 1,410 1,225 

Efficiency, % 27.7 22.6 - 20.7 14.9 16.6 

Note: 1. not recorded 

2. charcoal remaining; wood remaining

2. Methods of selecting stove materials such as fire resistant clay, 

insulating material, etc. and how to improve such materials. 

3. Government development and provision of the stove mold for mass 

production of the improved stoves. 

4. Government advertising campaigns to boost sales and marketing of the new 

stoves. 

5. Providing awards and incentives to cooperative manufacturers. Stove 

competitions and awards to manufacturers producing the most efficient 

stoves are highly recommended. Stoves that pass a standard test for 

efficiency and ruggedness should be given a government guarantee 

certificate. This will give the users confidence enough to buy and 

motivate manufacturers to produce good stoves. 

232

Figure 9.1 Introduction of developed stoves to participants 

Figure 9.2 Stove contest for efficiency comparison between 

commercial stoves and developed models 

233

Figure 9.3 Trainee participation in installing stove's parts 

Figure 9.4 Distribution of developed stoves to all participants 

234

Chapter 10 

Conclusions

CONCLUSIONS 

As a result of the implementation of the Improved Biomass Cooking Stove 

Component, many activities and achievements took place. Accomplishments can 


1. As a part of institution strengthening, the component has succeeded in 

establishing a cooking stove testing laboratory at the Forest Products 

Research Division, Royal Forest Department, Through project f.,nding, the 

laboratory was equipped with invaluable, basic test instruments and 

facilities--including a microcomputer system for future applications. 

2. Long-term training of project personnel to increase their future 

capabilities was minimum because time was short (30 months) and they were 

needed on site to carry outi.project tasks. Therefore, all technical personnel 

were indispensable for project implementation. They could not be spared for 

long term training. 

3. The component has produced five generic types of improved cooking stoves: 

namely, the charcoal bucket stove, wood stoves with and without chimneys, and 

rice husk stoves with and without chimneys. The absolute heat utilization for 

charcoal and both types of wood stoves increased up to 7% over that of the 

average commercial models. Further, an increase of 5 and 3% was achieved 

with rice husk stoves with and without chimneys respectively. In terms of 

comparative efficiency increases, the charcoal stove reached a 26% increase 

over the average commercial models, while for wood stoves with and without 

chimneys they were 58 and 35% respectively. The increase for the rice husk 

stove with chimney was 100%, or double the efficiency of the average 

commercial models. The rice husk stove without chimney had the least 

increase--15 - 16%. 

4. The investigation conducted on existing commercial stoves revealed that 

fuel efficient cooking stoves for charcoal, wood, or rice husk are rare. The 

laboratory tests have led to the identification of the stoves' critical 

physical parameters. They consist of stove weight; exhausted gap/area; 

combustion chamber capacity; rim design for proper fit of variously-si7ed 

pots and pans; grate-to-pot distance; grate parameters such as hole area, hole 

size and distribution, and thickness; height of chimney, and flue gas baffle 

(for chimneyed stoves). Other strong factors also influencing stove 

performance are external variables--fuel load or fuel feeding rate, amount of 

water to be boiled, and the wind factor. The information obtained was later 

used for redesigning the improved stove models. 

5. Good quality clay material suitable for stove manufacturing has been 

identified and a production technique has also been developed for small-scale 

and home industries. Local stove manufacturers in one district of Roi-et 

Province were trained without any difficulty in this technique of stove 

production. Improved stoves, particularly charcoal and nonchimney wood models, 

are heat refractory and can withstand thermal shock much better than present 

237

commercial ones. In addition, the application of the internal mold has 

greatly improved the precision necessary to control the critical internal 

dimensions. This metnod was found to be superior to the traditional one 

using an external mold which hardly controlled the internal dimensions. 

6. The production cost of the improved models as described in (2) above 

presently is approximately 2.5 times more than the cost of the poorer quality 

commercial models. However, when compared with top quality charcoal bucket 

stoves sold in the market, the improved models' cost is 25 - 30% lower, 

Therefore, in long-term commercial production, the improved models will be 

competitive when production increases and more improved stoves reach the 

market. 

7. So far, nine improved stove promotion and training programs have been 

carried out among villagers at various places around the country. The 

reception for the charcoal bucket and the non-chimney wood stoves was very 

good, while the good reception of the rice husk chimneyed stove was limited 

to a few localities where only rice husk is available. The chimneyed wood 

and non-chimneyed rice husk stove are of less interest to rural users than the 

c&arcoal bucket and the non-ehimneyed wood and the rice husk chimneyed stove. 

It is believed that with good follbw-up and promotional effort, some of the 

improved developed models will witastand harsh use and serve users well in 

rural kitchens. However, these long-term results are yet to be seen. 

8. Because of time constraints, the project had a limited time to approach 

manufacturers on a large scile. However, among a few large manufacturers in 

the Central area, the response to the idea of mass production of the 

developed models was not enthusiastic. This lack of enthusiasm is perhaps 

a result of stove manufacturers being accustomed to the production of their 

rough products and being reluctant to manufacture stoves with which they have 

little or no experience. Moreover, they probably want to see the market for 

high quality, efficient stoves develop first before committing their resources 

to their production. Therefore, more time and more education are needed for 

them to change their attitude and adapt their production techniques. 

238

Chapter 11 

Recommendations

RECOMMENDATIONS 

On the basis of the overall work of this project, some recommendations 

are presented below: 

1. Because stove development and promotion involve the social customs and 

habits of millions of people in Thailand and around the world, it is highly 

recommended that stove research and development be carried on to further 

improve present designs and find more alternatives for users. 

2. Stove development should ,mphasize each generic type of stove; namely, 

charcoal, wood with and without chimney, and agriresidue stoves with and 

without chimney so that users have choices. 

3. Stove research and development must not only emFhasize the good 

conversion efficiency, but it must also facilitate ease of use and other 

cooking functions, without causing undue change in people's cooking habits. 

4. Stove promotion is a most difficult activity. It will take a groat 

deal of time and resources. Therefore, continuous effort must be made for 

at least five years with reasonable financial and human resource support in 

order to see a real impact among 6 million rural users. 

5. In Thailand there are quite a few researchers and interest groups working 

on stove development and promotion. Unfortunately, all lack guidelines and 

coordination. For national stove programs to be directed toward this common 

goal, leading government agencies are needed to provide close coordination. 

6. During the course of stove development, many contacts were made with 

experienced stove manufacturers. It was found that, regardless of their 

long experience, their basic understanding of good stove configuration, design 

and its performance was very much lacking. This problem was also manifested 

in the presence of a large majority -I poor quality and less efficient 

commercial stoves in the market. 'nerefore, it is strongly recommended that 

concerned government agencies take an initiative toward arranging formal 

training programs for the promotion of the essential, scientific knowledge 

required among stove manufacturers. Incentives or approaches such as offering 

a certificate and/or reward to manufacLurers of efficient stoves would be 

a highly motivating factor. 

7. The lack of understanding among users on the criteria for selection and 

use of efficient cooking stoves was also evident. Therefore, the concerned 

government agency should establish a long-range,adequately funded educational 

campaign program for efficient stoves--particularly through primary and 

secondary school systems. 

8. The cost of improved design stove production is still high. If simple 

hydraulic molding can be developed and employed at the village level, 

production costs can be greatly reduced. Under these conditions stove 

dimensions wil be more precise and the production rate will be increased 

significantly. 

241 

7~

9. Selection of clay raw material and improvement of the clay mixture and 

firing to attain a product with fire resistant charicteristics (particularly, 

the charcoal stove body) are essential to a stove's long service life. The 

weight of the stove also needs further reduction (to achieve peak performance 

with even lower charcoal loads). 

10. The improved non-chimneyed.wood stove is quite efficient for the present 

developed model. IL can conveniently be used to replace three-rock stoves. 

However, the same problems exist in its mass production techniques as exist 

for the charcoal stove. 

11. Smoke in the kitchen is a problem inherent in non-chimneyed wood stoves 

including the three-stone and open fire. Research should be carried out in 

Thailand to determine whether smoke from undeveloped and even developed stoves 

(which noticeably gives less smoke over the undeveloped ones), has any 

significant effect on long-term health of users. 

12. Up to the present time, the one hole chimneyed wood stove has attained 

an efficiency up to only 18-19%. In addition, there are problems fitting 

pots and pans to this stove. Therefore, it is recommended that development 

on this type of stove be continued in order to improve both heat utilization 

efficiency and comparability with various pots and panb. Moreover, the stove 

material (as in the case of the non-chimneyed wood stoves and the charcoal 

stove) should also be investigated. 

13. Even though, at present, the chimneyed rice husk stove is still not 

popularly used in Thailand, the chance for this stove to become popular in 

certain regions is high. This is because it can use granulated fuels other 

than rice husk (such as sawdust, peanut shell, seed waste, household biomass 

scraps, etc). There are several further improvements that need consideration. 

These include the improvement of the stove's configuration to fit various 

pots and pans and reduction of its weight so that sometimes it can be moved 

around the house (yard) when needed. For two people to carry the stove, the 

weight should not exceed 50 kg. 

14. The experience gained from the stove promotional campaigns among rural 

users, even in its short duration, strongly indicated that the-! is a good 

chance of success in replacing relatively inefficient stoves ax..ng 6 million 

rural Thai families with efficient stoves. It is, therefore, recommended that 

the government support a nationwide efficient stove-promotional campaign for 

users and manufacturers as soon as possible. 

15. Since better biomass cooking stoves, in part, mean better living 

for millions of rural families around the world, the idea of 

continuous development to attain even better performance than the present 

developed models should be the challenging subject among applied research 

scientists and cuncerned institutions. 

242

ANNEX I 

Commercial Charcoal Bucket Stove Investigated

A ! 

wI 1/2 

245 

Stove No. 1/2 (Charcoal & wood) 

Name Heng Siem Lee 

Pot hole diameter 19, 23 cm 

Weight 12.2 kg 

Exhaust gap 2 cm 

2 

Exhaust area 96 cm 

2 

Grate hole area 112 cm 

Grate: grate hole area 1:0.46 

Fuel chamber size 2426 cm 3 

Time to boil 21.7 min 

HU 24.96 %

m J Jt(AIl 

~~~~~7 

- ,': W. . .. .- ...... 1 

ZZ 

246 

S, yoe No. /3 (Non insulated) 

Name Ifeng Siem Lee 

[lot hole diameter 19,24 

We I It 8.7 kq 

xhaust gap ].8CHI 

Exhaust area " cr-" 

Grate hole area 112 CI112 


Fuel chamber size 2426 cjn 


625.70 

CI

Stove No. 1/4 

Name Rungsit 

Pot hole diameter 19,23.5 cm 


,xhaust gap 1.5 cm 

Exhaust area 76 cm 2 

Grate hole area 112 cm 2 


F'uel chamber size 2426 cm 3 

4 Time to boil 18.8 mil 

I7 28.19 

247

~-iII -mm 

MT 

5 11nT.I Stove No. 1/5 (Stainless bucket) 

- Name~i Rung Sit 

248 

Pot hole diameter 16,20 cm 

Weiqhlt 9.3 kg 

ExIl.lst oap 1.0 cm 

( Ia',t.L 

.,41 

. I e ar ,s;l 

80 

2 

Cm 

("1112 

r;ate: grate hole area 1:0.45 

Fuel chamber size 1575 cni 3 


H4 30.53 %

15 ,2 1/5 2 

Stove No. 1/5 

Name Rungsit 


Weight 9.3 kg 

V Exhaust gap 1.0 cm 

249 


2 



Fuel chamber sine 1575 cm 3 

Tine to l,n il 21.1 n i.n 

flU 30,53 %

1 /6 

.......... AL . 

6ir#rfv 

.7 Stove No. 1/6 

250 

Name Rungsit 


Weight 8.6 kg 

Exhaust gap 1.0 cm 






H 28.83 %

,". f u 

251 

5 

Stove No. 1/7 

Name Ayudthya 

Pot hole diameter 

Weight 

Exhaust gap 

Exhaust area 

Grate hole area 

Grate: grate hole area 

Fuel chamber size 

Time to boil 

21 cm 

6.4 kg 

2 cm 

63 "m2 

66 cm 2 

1:0.23 

-4 

1931 cm 3 

28 min 

2 5 .6 1%

1/8 

,%, .,;,M-_ Stove No. 1/ 

252 

Name unknown 

Pot hole diameter 18 cm 

Weight 8.1 kq 

Exhaust gip 1.5 cm 


Grate hole area 48 c2n 



Time to boil 27 min 

IlU . 

24.07

, - .- , .. 

Stove No. ]/9 

Name Chachernrsat 

lot hole dianeter 23 cm 

Weiqht 8.7 kg 


Exhiust area 66 cm 2 

Gr~ite hole qrea 94 cm 2 

Grt.e: grate hole area 1:0.28 

Ftel chaimber size 3232 cm 3 

Tire to boil 23 mill 

'7 H28.42 % 

253

1/10jrf 

i,~ 

-m • 

-W 

7 Stove No. 1/10 

254 

Name unknown 


weight 4.2 kg 



2 





HU 26.54 %

Stove No. 1/11 

Name unknown 


Weight 4.2 kg 

iExhaust gap 2 Cin 

255 

lIxi ,;astrea 80 111 

2 




HtU 26.52 %

A 


Name Booppararm 

Pot hole diameter 22 CM 

Weight 7.2 kg 

N Exhaust gap 2 cm 

256 

Exhaust area 8c cm 2 





flu HU29.02 %

--- 2 -r- :- .... ..... . 

1 kStove No. 1/13 

Name Samyakphicharg 

$ Pot hole diameter 22 cm 

257 








HU 26.12 %

258 




Weight 19 kg 

Echaust gap 2.5 cm 


Grate hole area 65 cm2 



Time to boil 27.2 in 

HU23.53 

flu %

low 


1 ! Name Banglion& 

259 

PoL hole diameter 20 cm 

Weiqht 10.0 kg 


Exhiius area 108 cm 2 

(:riLe hole grea 65 cm 2 

o(Irite: grate hole area 1:0.23 

Iuf chamber size 2865 Cm 3 

927.21 

'nto)boil 24.26 mi

260 

11M 

Stove NO. 1/16 

Name Ayudthya 


Weight 6.6 kg 


Exhaust area 45 cm2 

Grate hole area 59 cm2 

Gr,-te: grate hole area 1:0.2 

Fuel chambe ie 268cm3 

Time to boi.1 27.2 rain 

HIU 27.45 %

1/17 

261 


Name Cholburi 


Weight 5.9 kg 

E*:xhaust gap 

Lxhtu'L area 

rate nole .area 

(;rate: grate 

Fuel chamber 

Time to boil 

Hu 

hole 

size 

1.2 

50 

54 

area 1:0.31 

2013 

20 

32.30 

cm 

Cm 2 

C1m 

2 

cm 3 

mir 

%

262 

W.1 


Name Cholburi 


Weight 

l:xhausL t ap 

Exhaus t area 

Grate iole area 


Fuel 

Time 

chamber 

to boil 

21 ci 

7.2 

2 

96 

68 

1:0.25 

size 3202 

23.6 

IHU 26.85 

kg 

cm 

cm 2 

cm 2 

cm 

mill

4 ,4 


Name Samrong 




Exhaust area 105 

2 

cm 

4, 1I (;rate hole area 94 CHI 2 

263 


Fuel chamber size 3X42 cm 3 


flU 23.94 %

4 0 

4.4 1, 

V fe 

14Stove No. 1/20 

264 

Name Cholburi 


Weight 

Exhaust gap 

Exhaust area 


(;rate: grate hole 


Time to boil 

23 

10.2 

2 

102 

94 

area 1:0.30 

2516 

30.3 

cm 

kg 

cm 

c mn 

C1 2 

cmn 3 

mill 

flflu 24.49 %

'265 

265 


toe DaNo. 1/2 

Pot hole diameter 22.5 cm 


Ixhtus t caj 3 cm 

I.xhaust area 107 cm 2 

(Grcate hole grea 68 cm 2 

Grite: grate hole area 1:0.22 

uel cliamber size 2414 cm 3 


HU " 

24.13 %

266 


Name Barnponge 


Weight 9.5 kg 





Fuel chamber size 3155 cm, 

Time to boi.] 23.3 min 

flu 28.11 %

J/23i tr LJ UV 

Stove No. 1/23 (non insulated) 

Name Heng Siem Lee 


W; Weight 7.2 kg 

267 

: ull,-I St: qap 1 On 

Ix'hwA t o4trea 41 cmI2 

GtL, ti hole area 80 (:l 2 

(;rate: grate hole area 1:0.45 



IU 29.17 %

A Name Cholburi 

268 

Stove No. 1/24 (Charcoal & wood) 



Exhaust (lilt) 2.2 cm 

1.xh.iust aroa 112 cm 2 

Grate hole a rea 77 1i1 2 




flU 25.9 %

269 

Stove No. 1/25 Charcoal & wood) 

. Name .le~ Sie-m Lpe modified 

Pot. hole diameter 19,23 cm 

We I 13.2 kg 

.Xhmat yap cm 

2 

Exhast area 96 cm 

(;rate hole area 112 cmI 2 a 


1-'uel chamber size 2426 cm 

,ime to boil 11.8 min 

lu 26.59

i % 

I' 

g 

b 

", -Grate: 

S' 

:: i"Fuel 


Name Darnkwian 

, Pot hole diameter 

270 

Weight 

Exhaust1%";I 

gal 

Exhaust area 


grate hole area 

chamber size 

Grte 

oth grt ol o~ ra 

(non insulated) 

23 

66k 

1.5m 

90 

752m 

1:0.24 

270 0 

23 l24 

cm 

cm2 a 

cmm

L- A 

97ttv 


YName Sa Sua 

A'M 




2 


04at", +1Grate hole area 74 cm 2 

1 Q I,!IGrate: 

grate hole areal:0.24 

271 

3 

Fuel chamber size 4261 cm 

Time to hoti] 20.1 mi 

IU 25.10

272 


Name Sa Sua, modified 

Pot hole diameter 19 cm. 

Weight 13.2 kg. 

Exhaust gap 2 cm. 

Exhaust area 85 cm. 2 

Grate hole area 74 cm. 2 


3 

Fuel chamber size 3414 cm. 

Time to boil 20 min. 

HU 28.85

,:,1/30 So N 

Name Nakornchaisee 

Pot hole diameter 2(J,24 cm 

Weight 18 kq 

\Exhaust qap 1.5 cm 

... area 72 dir 2 

rs 

t;ra to he Ie area 111 cm 2 

(Grate: grate hole area 1:0.46 



.......... fu 24.25 % 

273

01. 

rr 

274 


Name nakornchaisee 


Weight 

Exhaust gap 

Exhaust area• 

(;rate hole area 

Grate: grate hole 


Time to boil 

SliU 

area 

17,20 

11.8 

o.5 

20 

94 

1:0.44 

9')50 

16.7 

32.3q 

cm 

kg 

cm 

C1112 

c1,12 

Cmn3 

rmin

~I 


Name NAkornchaisee 


Weiqht 8.2 kg 


2 



* (;rate: grate hole areal:O.46 

275 

3 


Time to boil 17.6 mill 

IfU 24.61 %

:%: 'S tove No. 1/33 

P, Name Nakornchaisee 

276 

[Pot hole diaueter 17,20 cm 

We iqht 6.7 kg 


Exhaust area 20 Cm 2 

Grate hole grea 94 cmn!l 

irat.e: grate hole area 1:0.41 

'utelchamber size 2550 cm. 

2u6 to bol 18.3 ii 

jIG 30.51

wnI 1/34 

SlU 

277 


Name Bang Sue 


Weight 

10.4 

Exhaust gqap 1.8 cm 

Exhaust area 103 

2 

cm 

Grate hole area 68 


luel chamber size 

2829 

kg 

2 " 

cm 

3 

Cm 

'Tillie to ho i 21.2 inin 

26.07

I Stove No. 1/35 

'Name Bang Sue 

278 

U- 


Weight 8 kg 

Exhaust qap 1.7 cm 

2 


Grate hole area 54 ctll. 


Fuel chamber size 2176 cm3 


IlU 27.22 

I1AJ

!Y'IfJ u I/36 

•. 

279 

.;Iw 

.~ ~..... .i ..... . 


Name Bang Sue 

IPot hole diameter 

weiht 

Ilxhaust 

Exhaust 

gap 

area 

15 

6.5 

56 

1.5 

cm 

kg 

cm 

cm 2 




area 1:0.31 

1568 cm 3 


Il u 30.67 %

37mm 

I- 

-iQj 

il O 

.0 280 

" 

280 



Pot hole di ameter 15 cm 

Weiht 

Exhaust gal) 

Exhaust area 



,uel 

Time 

1.U 

chamber size 

to boil 

6.5 

0.7 

30 

25 

1:0.14 

1140 

26 

28.07 

kg 

cm 

cm 2 

cm 2 

cm3 

rni1

., 

281 

1/3 1i/31 1 

1 , , 

Stoveinc'd1/38 

Name? unknown 

[loat hole 

weiqht 

Li:xhaust gap 

xhaust area 

(SaLe hole grA 

diameter 19,22 

grate hole 

1.*Iim-l chamber size 

10 

1.9 

12,cm 

70 

area 1:0.35 

2000 

cm 

kg 

cm 

2 

cm 2 

cm 1 

TL to boil 20 rain 

Ilu 

27.7

1/39 

.... ,Stove No. 1/39 

*cm 

-,,. Name Cholburi Dab.modified 

.4 ' Pot hole diameter 

Weight 

22.5 

8 

cm. 

kg. 

' Exhaust gap0. cm 

6 J "6. xhaust area 47 c~ 

282 

Grate hole area 57 cm./ 

Grate: grate hole area 1:0. 2 8 

Fuel chamber size 2800 cm. 3 

Time to boil 17 min. 

HU 33.35 %

ANNEX II 

Commercial and User Built Wood Stove 

Without Chimney Investigated

Stove No. 2/1 

Name Roi-et (Original) 


Weight 5.9 kg 


Exhaust area 25.3 cm 2 

Grate hole area - cm 2 

Grate: -trate hole area - 



flu 17.59 % 

285

Stove No. 2/2 

Name Thick dome, clay 

7A 




Lx h,ust- area 18.2 (:m 2 

raL' hole arca - c= 2 

Grate: grate hole area - 



fHU 19.25 % 

286

n n " 21,.3 1 r;.: i ii .. . -... 

Stove No. 2/3 

Name Thick horse shoe, clay 








Time to boil 13.7 rain 

HU 19.08 % 

287

Stove No. 2/4 

Name Morn Pakred, modified 


Weight 2.5 kg 



Grate hole area 160.9 

2 

cm 


Fuel chamber size 7440 

3 

cm 


fu 20.94 % 

288

Stove No. 2/5 

Name Morn Pakred, 


Weight 

Exhaust gap 

.twti;L i ea 

(Cl. .. hole ,reii 



Time to boil 

Ifu 

2/ ifIliIjln/ 

289 

small 

area - 

18 cm 

12 kg 

5.0 CM 

210 (Ml2 

2 

CII1 

3600 cm 3 

17 min 

23.27 %

Stove No. 2/6 

Name Tripod 

Pot hole diameter - cm 

Weight 0.7 kg 

Exhaust gap - cm 

Exhaust area - cm 2 



Fuel chamher size - cm 1 

T ime to h) i 1 16.2 rain 

flu 1.4.2 

290

Stove N''. 2/7 

Name Morn Pakied, largo 

PoL hole diameter cm 

Weiqht 3.3 kg 



2 

Grate hole grea - cm 

Grate: grate hole area 

L.u1 chimber size 7440 cin 3 

T ime to boil 18.7 1 in 

iU 15.39 

291

Stove No. 2/8 

II- 

Name Modified Roi-et, clay 

Pot hole diaweter 22 cm 

Weight 6.6 kg 

Exhaust gap 1 tm 

lxI,iu.L aera 

Crate holetare, 


2 

55.5 cm 

2 

99.6 Cni 

Fuel chamber size 4560 Cm 3 


ftU 20.92 

292

Stove No. 2/9 

Name Horse shoe, 

Pou hol.e diameter 

Weight 

Exhaust gap 

Exhaust area 




clay 

25 cm 

8.1 

2.5 

197.1 

area - 

- 

kg 

cm 

cm 2 

cm 2 

6380 cm 3 


flU 19.48 

293

2/10 Mlletu"41 

1"i 0 i0 w 

Stove No. 10 

Name Thin horse shoe, clay 


Weight 7.4 kg 


Exhaust area 77.6 CM 2 

Grate hole area cm7 


Fuel chamber size 4560 cm3 


IfU 16.77 % 

294


Name Dome, clay 


Weight 15 kg 



Grate hole area 160.9 cm 2 




flu 

295 

20.2

7j 

:.~~ ~~21 m It/6 :++ ,.. 


Name Pot shaped, clay 

Pot hole diawiioeer 22 cm 

Weicjht 10.3 kq 


2 

Exhaust area 86.4 cm 

Grate hole area - cm2 


3 



flu 14.37 % 

296

12/222 l-j~lbS 


211, 

Name Dome with cap, clay 





Grate hole grea 160.9 cm 2 

GraLe: grate hole area 1:0.34 

lue chamber size 6840 cm 3 


IIU 24.4 % 

297

Mi 


Name Modified Roi-et, clay 


Weight 14 kg 

E~xhaust q(q) 1.8 cm 

kxhIust ar a 86.6 cm 2 


Grate: grate hcle area 1:0.34 


Time to boil 14.5 mill 

IIU 23.2 % 

298

IA 

*:!2/24 irnitzrn 


Name Cylinder, steel 


Weight 3.7 kg 


Exhaust area 

32.2 

cm 

2 

Grate hole area 99.6 cm 



2040 

2 

3 

cm 


HU 25.93 % 

299

ANNEX III 

Commercial Wood Stove with Chimney Investigated

.L 

,Stove No. 2/11 

Name Saengpen, Narn 









HU 13.88 % 

S..303

304 


Name Samrong, Samutprakarn 







Fuel chamber size 4400 u,3 


flu 1UI].99 %

7." 

305 

• 

Stove No. 

2/15 

Name Ban Pong, Rajaburi 

Pot hole diameter 29.0 

69.5 

Weight 695 

Exhaust gap- 

Exhaust area 

(;rate hole grea 

23.8 

94.3 

cm 

kg 

cm 

cm 2 

cm 2 

GraLc: grate hole area 1:0.20 

l-'uelchambet size 5890 cm 3 

Tree to bo' 16.7 min 

IU 11.01

ANNEX IV 

Commercial Rice Husk Stove with Chimney Investigated

309 

VC,' 

Stove No. 3/2 

Name Ngo Gew Ha 

Pot hole diameter 32.0 cm. 


2 

Flue gas outlet area 78.0 cm 

3 

Fuel chamber size 19,000 cm 

Chimney height 240 cm 

Pot used, 24 cmHU 5.48%,TTB 20.0 mi

Stove No. 3/4A 

Name Thai charoen 

_VI Pot hole diameter 33.0 cm. 


Flue gaIs outlet area 47 cm 2 

Fuel chamber size 16,400 cm 3 

Chimney height 240 cm. 

Pot used, 24 cm,IIU 6.24%,TTB 23 min. 

Pot used, $ 30 cm,HU 9.26%,TTB 24.3 min. 

310

Stove No. 3/4B 

Name Thai Charoen 



2 

Flue gas outlet area 95 cm 

Fuel chamber size 12,600 cma 


Pot used, 0 30 cm,HU 8.53%,TTB 28.3 min 

Pot used, 0 24 cm,HU 7.23%,TTB 25 min. 

311

Stove No. 3/5 

Name Banglane 



, , Flue gas outlet area 113.0 cm 2 

312 


Chimney height 230 cm 

Pot used, 30 cm,HU II.14%,TTB 20.3 min. 

Pot used, 24 cm,HU 4.24%,TTB 28.5 min.

(o5 ~Flue % 

Stove No. 3/6 

Name Sayan 



gas outlet area 

2 

28.0 cm 

3 

Fuel chamber size 6,200 cm 


Pot used, 24 cm,HU 7.13%,TTB 27.0 min. 

313

314 

Stove No. GC2 

Name Sooksunt 

* , 


Weight 62 kg. 

Flue gas outlet area 71.0 cm 2 



Pot used, 6 24 cm,HU 9.23%,TTB 21.7 min.

ANNEX V 

List of Staff for Stove Improvement Component

ANNEX 3 

List of Staff and Personnel for Stove Improvement Component 

1. Dr. Aroon Chomcharn 

2. Mr. Arkom Vejsupasuk 

3. Mr. Songdham Jaikwang 

4. Ms. Malee Rungsrisawadh 

5. Mr. Piroj Uttarapong 

6. Ms. Pojanee Jongjitirat 

7. Mr. Banyat Srisom 

8. Ms. Nongluck Thong-in 

9. Mr. Wattanapong Woottha 

10. Ms. Sudarat Ngamkajohnwiwat 

11. Mr. Pratya Kanapoosed 

12. Ms. Kevalee Musikapong 

13. Mrs. Kunthon Santudkarn 

14. Mrs. Lek Ninmanee 

15. Mrs. Hame Krisangsri 

317 

Component leader, RFD 

Assistant comp. leader, RFD 

Project officer, RFD 

Project officer, RFD 

Project consultant, Kasetsart Univ. 

Project consultant, King Mongkut's 

Institute of Technology 

Project consultant, Temp. employee 

Project researcher, Temp. employee 


Piojcct researcher, Temp. employee 


Project coordinator, Temp. employee 

Supporting service, RFD 

Stove fabricator, RFD 

Stove fabricator, RFD

REFERENCES 

'', 

"1"'":'J':" '. 'IIi . : . .j\

REFERENCES 

Bennett, C., Myers, J.E., Moment'm, Heat and Mass Transfer, McGraw Hill 

International Book Co., Singapore, 2nd ed., 1974. 

Bird, R.B., Stewart, W.E., Lightfoot, E.N., Transport Phenomena, Wiley 

International Edition, New York, London, John Wiley and Sons, Tn-., 1960. 

Bronowski, J., The Ascent of Man, Little, Brown and Company, Boston, 1973. 

Bumroong, T., Economical Stove, Appropriate Technology for Education, 

Institute of Educational Promotion for Science and Technology, Ministry of 

Education, Bangkok, pp. 61 - 65, 1981. 

Catlyn, A., Joseph, S., and Shanahan, Y., Testing of the Zip Stove, 

Intermediate Technology Development Group, Stoves Project, Technical Notes 

No. 3, 1983. 

Chomcharn, A. et. al., Energy from Wood (5): Test for Efficiency of Fuel 

and Bucket Stove, Forestry Meeting Annual Report, Forest Products Research 

Division, pp. -29 - 254, 1981. 

Cookstove Bulleting, Priyagni: A New Stove from CPRI, Tata Energy 

Documentation and Information Center, Bombay, pp. 4 - 5, 1984. 

Cookstove Handbook, Pilot edition, Tata Energy Research Institute Documentation 

Center, Bombay, 1982. 

Deeammart, L., Economical Stove, A Report on Stove Testing and Evaluation 

Using Agriresidue, Military Research and Development Center, Supreme Command 

Headquarter, pp. 61 - 63, 1981. 

Dunn, P. et al., Traditional Thai Cooker, Energy from Biomass: 2nd E.C. 

Conference, pp. 748 - 752, 1982. 

Forestry Statistics 1982, Forest Statistics Section, Planning Division, 

Royal Forest Department, p. 9. 

Foley, G. and Moss, P., Improved Cooking Stove in Developing Countries, 

Earthscan, Energy Information Programme, Technical Report No. 2, ITED, 

London, 1983. 

Gupta, C.L., Usha, K., Energy Vol. 5, pp. 1213 - 1222, 1980. 

Hoel, P.G., Introduction to Mathematical Statistics, Wiley International 

Edition, John Wiley and Sons, Inc., New York, London, Sydney, Toronto, 

4th ed., 1971. 

Joseph, S., Stove Testing, ITDG, 1979. 

321 ''

Joseph, S., Shanahan, Y., Trussell, J., and Bialy, J., Compendiwn of Tested 

Stove Designs, ITDG Stoves Programme for the UN Food and Agricultural 

Organization, 1980. 

Kaufman, M., From Lorena to a Mountain of F,"' , A case study oi Yayasan Dian 

Desa's fuel efficient stove program 1978 - 1983. 

De Lepelaire, G., Prasad, K.K., and Verhart, P., A Wood Stove Compendiiun, 

Prepared for the Terhnical Panel of Fuelwood and Charcoal, UNERG, Nairobi, 

1981. 

Madon, G., L. DIOP and E. Lagandre, Leo Consommatione de Combustibles 

Domestiques au Senegal Sur Foyers Traditionnels et sour Foyers Areliorees, 

CERER, University of Dakpr and USAID, Undated. 

Meechai: Economical Stove, Papers from Family Planning and Public Development 

Association, 8 Sukhumvit Rd., BKK 11, undated. 

Noi, P., EconomicaZ Stove and Charcoal Fuel, Appropriate Technology for 

Education, Institute of Educational Promotion for Science and Technology, 

linistry of Education, Bangkok, pp. 115 - 129, 1981. 

Omar, K.J., Chula-Need for Improvement, Dept., of Chemical Engineering, 

BUET, Dacca, Bangladesh, Undated. 

Openshaw, K., A Comparison of Metal and Clay Charcoal Cooking Stoves, 

Division of Forestry, Faculty of Agriculture, Forestry and Veterinary, 

Science, University of Dar es Salaam, Morongoro, undated. 

Osuwasn S. and Booyakiat, K., Study of Varic-bles Affecting Charcoal Stove 

Efficiency, Journal of Chemical Engineering Food and Fuel Technology, 

pp. 5 - 95, Bangkok, 1982. 

Perry, R.H., Chilton, C.H., Chemical Engineers' Handbook, McGraw Hill C-., 

5th ed., 1973. 

Ponnoum, S., Wongopalert, A., Arnold, J., Jr., Stove Experiments and Cooking 

Observations, Meat Systems Inc., Thai Group, February, 1982. 

Prasad, K.K. , ;orwel Perfor iaen [oots on Open Firec and the Family Cooker, 

Woodburning Stove Group, Department of Applied Physics and Mechanical 

Engineering, Technical University of Eindhoven and TNO, Apeldoorn, 

Netherlands, 1980. 

Prasad, K.K., A §tud U on the Perfo2vwaicc of 'iso14etalovcs , Woodburning 

Stove Group, Technical University of Eindhoven and TNO, Apeldoorn, 

Netherlands, 1981. 

Prasad, K.K., S'ome Studleo on Open Fires, Shielded (0i HadeaO':" Stoves, 

the Woodburning Stove Group, Eindhoven University of Technology and TNO, 

Apedoorn, Netherlands, 1981. 

322

Sherman, M. and Srisom, B. et al., Thailand National Renewable Energy Project, 

Interim Report of 1982, Activity Stove Improvement Component, 1983. 

Singer, H., Report to the Government of Indonesia on Improvement of Fuelwood 

Cooking Stoves and Economy in Fueloood Constaption, Report No. 1315, FAO, 

Rome, 1961. 

Sooksant, S., Economical Stove for Rural Village, Appropriate Technology for 

Education, Institute of Educational Promotion for Science and Technology, 

Ministry of Education, Bangkok, pp. 71 - 89, 1981. 

Suwat, T. and Paitoon, M., Cooking Stove Using Agriresidues as Fuel, 

Department of Mechanical Engineering, Songkhla University, undated. 

Tata Energy Research Institute, Documentation Center, Bombay, 1979. 

Thomas, L.C., Fundcientalsof Heat Transfer, Prentice Hall, Inc., Englewood 

Cliffs, New Jersey 07632, 1980. 

Vita News, Report from Upper Vol-,,, New Direction in Wood Stoves, 

pp. 8 - 9, 1984. 

Walpole, R.E., Myers, R.H., P2,obability and Statistics for Engineers and 

Scientists, McMillan Publishing Co., Inc., New York, Collier McMillan 

Publishers, London, 1972. 

323

improved biomass cooking stove for household use - (PDF, 101 mb ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?