Cover Image
close this bookBoiling Point No. 05 - September 1983 (ITDG, 1983, 20 p.)
View the document(introduction...)
View the documentAcknowledgements
View the documentNews From Shinfield
View the documentOctober/November Stove Meetings
View the documentBP No 4 ...
View the documentTN No 3 ...
View the documentStoves Training Course
View the documentNews from Fondation de Bellerive
View the documentCharcoal Stove Testing at Dian Desa, lndonesia
View the documentAprovecho Internships
View the documentPottery Stove Production in Sri Lanka, India, and Indonesia
View the documentHotel Cookstoves in Mangalore, India
View the documentMud: Rice Husk Stoves of Indonesia
View the documentImproved Stoves in India
View the documentChimneys
View the documentBook Reviews
View the documentITDG Stoves Project Recent Publications

(introduction...)

IT Intermediate Technology

Acknowledgements

Technical Editors:

Stephen Joseph


Yvonne Shanahan

Artwork:

Jenny Trussell

Production:

Sandra Conn

Contributors:

Siddhartha Bhatt et al


Stephen Joseph


Brian MacGarry


A Mandal


Waclaw Micuta


Rajendra Prasad


Yvonne Shanahan


Aryanto Soedjarwo


Bill Stewart

(Readers wishing to enter into correspondence with any of the authors may obtain full postal addresses from the Stoves Project address given opposite)

ISSN 0263-3167

'Boiling Point' is the newsletter of the Intermediate Technology Development Group Stoves Project. Contributions are welcome in the form of articles of not more than 700 words with line drawings, simple graphs, etc. where appropriate. Copy date for the next issue is 1st December 1983.

All correspondence should be addressed to: 'Boiling Point', ITDG Stoves Project, Applied Research & Section, Shinfield Road, Reading, UK, RG2 9BE.

Opinions expressed in contributory articles are those of the authors and not necessarily those of the ITDG Stoves Project.

News From Shinfield

Since the issue of the last 'Boiling Point' in which we announced Stephen Joseph's impending departure from England, we have had many letters wishing Stephen good luck and expressing regret at his departure. As explained in issue No 4, Stephen has been making regular inputs to the Stoves Project as its Principal Consultant since April this year, but we did not clarify the continuing relationship between ITDG and Stephen. In 1984 Stephen will be based in Australia but he will not be giving up on Stoves. He plans to continue as our Principal Consultant for approximately four months a year, and spending about three months of this time in Reading. He will still be very much part of the IT Stoves team and a major resource in an expanding ITDG Biomass for Energy Programme.

Since April this year Yvonne Shanahan has been Acting Manager of the Stoves Project. She is now preparing to become the Chief Field Officer when she makes way for the new Project Manager, Mrs Yvette Stevens, who will be joining the team in October.

Yvette is a Sierra Leonan electrical engineer, trained at the MOSCOW Power Engineering Institute, and at Imperial College, London. For the past three years she has been working in Ajit Bhalla's Technology and Employment Branch at the International Labour Organisation in Geneva. Her main activities there related to income and employment creating projects in rural Africa.

October/November Stove Meetings

The Food and Agriculture Organisation is holding a three day consultation meeting in Rome during the last week of October, 'to provide a preliminary assessment of the impact of wood burning stove programmes, particularly in terms of fuel economy, acceptability of stoves, and speed of diffusion, of time requirement and scale of action'. It is hoped that this preliminary evaluation will 'ultimately provide planners and policy makers with some concrete indications of the real potential of wood burning stove programmes'. The purpose of the consultation 'is not to discuss the technical problems involved in stove design, dissemination and evaluation, but to examine the complex inter-action of technical, socio-economic, institutional and political aspects which influence the impact of such programmes.'

A small number of knowledgeable experts from Africa, Asia and Latin America have been invited to attend, and they will each present a paper on their programmes. Stephen Joseph has prepared a background paper for presentation at the meeting.

Several of those attending this meeting will then travel to Holland for the International Workshop on Woodstove Dissemination. The organising committee for this meeting is A Caceres (CEMAT, Guatemala), N Islam (Bangladesh University), Stephen Joseph, Madame J Ki-Zerbo (CILSS, Sahel), and K Krishna Prasad (Eindhoven University).

The specific aims of the workshop are to:

a) review and synthesise selected on-going woodstove projects;

b) develop a set of plausible dissemination strategies that

i) can contribute to superior domestic environment, and
ii) can make a dent on fuel consumption at the macro level;

c) initiate follow-up work to identify the relative effectiveness of the strategies considered in b);

d) draw up a range of options for the design, assessment and implementation of stove programmes consistent with the scale of the problem.'

The initial meeting in October will be followed by field projects in 1984 in six countries focusing on possible strategies for large scale dissemination of stove technologies.

A final meeting will be held towards the end of 1984 or early 1985.

ITDG Stoves Project personnel are closely involved in these meetings the outcome of which will be reported in the next issue of Boiling Point.

BP No 4 ...

SOLAR COOKER FROM ZIMBABWE


We must apologise to Brian MacGarry ('Alternative Cooking Stoves - Zimbabwe in BP No 4) for misinterpreting two separate drawings he sent us of the solar cooker, and combining them to arrive at a cooker with a door too small for the pot inside! We had assumed the cooker was a 'top loader' but the traditional African dish of sadza or ugali must be stirred about 30 minutes before serving, and to remove the pot through the lid to do this would lose too much heat from the cooker, so the side door is necessary.

Mr MacGarry bases his choice of cooker sizes on the requirement of 1,000 sq cms of glass 'window' in the top for each litre capacity of the pot. This is on the assumption that, at that latitude, a flat plate inclined at 25 degrees to the horizontal, and facing north, will receive between ' and 6KWh / day / sq m all the year round.

So the popular 3 litre enamel cooking pot requires a cooker 'window' of 55cm by 55cm, and the door is 20cm square which will not admit a larger sized pot. A 2 litre size pot requires a 'window' of 45cm x 45cm, and a door 17 cm high by 18 cm wide.

Mr MacGarry points out that for most climates in many inhabited areas of the world, the cooker would need to be even larger relative to the pot. He provided us with brief details of his glass area calculations, which we will be pleased to supply - or which could be obtained from him in greater detail.

TN No 3 ...

THE ZIP STOVE

We have continued our correspondence with the ZZ Corp about the Zip Ztove on which we presented a Technical Note (No 3) issued with BP No 4. We hope to include some further discussion about the stove's performance in the next issue.

The ZZ Corp informs us that the Woodburning Stove Group at Eindhoven University has increased the efficiency of the Zip Ztove from 31% to 40.25%. New operating instructions are now available for the stove, from the ZZ Corp, 10806 Kaylor St, Los Alamitos, California 90 720, USA.

Stoves Training Course

Mr Ozer Belir and Mr Mustafa Tumerdirim, Foresters from Turkey, attended a three week training course at Shinfield during May. Their study tour was sponsored by the FAO, and before coming to Shinfield they visited the Woodburning Stove Group in Eindhoven, and went on to spend a week with Waclaw Micuta in Switzerland.

Metal stoves for wood burning are used extensively in Turkey, and legislation is now being drawn up to prohibit the manufacture of stoves with a thermal efficiency below a prescribed level. Low interest credit has been offered to village families living in or near forest lands to purchase improved wood burning cooking and heating stoves.

According to the 1980 census 56X of the population of Turkey lives in rural areas, and consumes 60% of the firewood burnt in Turkey. It is estimated that 60% of the total heating energy required in Turkey (both urban and rural) is obtained from wood-burning.

Mr Belir and Mr Tumerdirim are shown testing a metal stove which they designed as part of the course, and which they helped to construct. They were aiming at producing an efficient wood burning stove, with an oven, which could be adapted during the cold season to provide room heating. It was also desirable that the stove be relatively simple and cheap to manufacture (in Turkey).

The initial test results showed that the stove was 75% thermally efficient when used for heating. The heat transfer to the hot-plate was good, but was poor from plate to pot. One method to overcome this would be to use various sized removable rings to sit differing sized pots over the firebox instead of on top of a hot-plate, but there was not time during the course for the Foresters to make and test this modification.

In parallel with the training course run specially for the needs of the Turkish foresters, another course was held which included the construction and testing of a small charcoal burning metal stove, and also mud and ceramic stove design, construction, and testing. This course was attended by two University of Reading students from Africa (Zambia and Tanzania, - studying for the M. Sc. course in Alternative Energy for Developing Countries), one of the lecturers for this MSc course, and an engineer from another section of ITDG. Many of the lectures in basic theories, for example on heat combustion, and stove design, and the workshop exercises, for example in metal work, were attended by the participants of both courses.

In the students' evaluation of the course they said that a longer period of time, that is, 4 weeks or more, would have been preferable in order to develop more of the practical and analytial skills required for implementing stove programmes.

News from Fondation de Bellerive

'MODERN STOVES FOR ALL' by Waclaw Micuta is currently being revised and is expected to be published in the near future. m e revision has keen commissioned by the French organisation GRET/GERES. m e principal modifications are the inclusion of a new chapter devoted to 'cooking methods', and extended sections on the preparation of clay materials and stove testing. A new Kenyan Jiko charcoal stove is included, and a chapter on the use of charcoal. In addition, the specifications of the 'Pogbi', 'Polish', and 'Crescent' stoves have been improved in the light of field experience.

COMMUNAL STOVES

During a trip to Kenya earlier this year Mr Micuta, and his colleague Emil Haas, developed 'communal' stoves to meet the needs of schools, dispensaries, hospitals, and similar institutions.

Two versions are described. Both are constructed according to the same principles and techniques, only the dimensions differ. As can be seen from the drawings, they are based on the 'Polish' and 'Crescent' models. m e first is a universal version equipped with a 42 litre pot for all purpose cooking. The second has been modified for 'Ugali' preparation, which requires a sturdy, relatively shallow pot, with a large diameter. m e clay and brickwork involved presents no major difficulties for trained masons. Once all the materials have been prepared, one mason working with 2 helpers should be able to construct a plinth and stove within 2 days.

The firewood economy achieved was considerable. For example, the cooking time for dry beans was reduced from 4-5 hours to 15-30 minutes. This dramatic reduction in cooking time is also due to the fact that the beans were pre-soaked.


FIGURE

In use it is not necessary to put more wood in the stove after the food has boiled. Instead the door should be closed and a bag of hay placed over the covered pot. The stove then acts as a hay box. When any foodstuffs were pre-soaked the consumption of firewood needed to cook a meal of beans and dry corn could be reduced from approximately 50kg to 6kg.

Stove Testing in Kenya

In Cookstove News Vol. 2 No. 3 Stephen Joseph outlined the results of 'Ugali' cooking tests carried out on a range of stoves at Ruthgiti in the Karai District of Kenya. Since then a series of follow-up tests have been carried out by Joseph Ngugi. Joseph Njoroge and Janevah Wanijiku, trainees of Waclaw Micuta (Fondation de Bellerive). The cooking tests were carried out with maize and beans to establish the performance of the stoves for a meal that takes up to 3 hours. A mixture of half each of maize and beans was cooked with water in Pot 1. Unfortunately, uniform quantities of food and water were not used in testing each stove. However, a consideration of the Specific Fuel Consumption ratios allows reasonable deductions to be made on performance.

The cooking test was carried out on the following stoves

- open fire
- Pogbi (2-pot chimney stove)
- a shielded open fire
- two modified Tungku Lowon stoves (I and II in the Table) - 2 pot chimneyless stoves.

It should be noted that only the open fire, the Pogbi and shielded fire were previously tested with 'Ugali'.

The Table below shows the results obtained.

Summary of Conclusions

It can be seen that the new stoves cook faster than the open fire, even when taking into account the differing quantities of food processed. When only Pot 1 is considered, it appears that the modified Tungku Lowon models used significantly less wood than the open fire. If the second pot is considered then both the Pogbi and the chimneyless stoves are far more fuel efficient than the well tended open fire.


FIGURE

Charcoal Stove Testing at Dian Desa, lndonesia

Charcoal is a widely used and sold fuel in Java, the most populous island of Indonesia. It is usually made in the mountainous forest areas and then brought down to the main markets in the cities and towns. It is rarely used in rural areas. Most charcoal is sold by the kilogram, often packed in 1 kg plastic bags. The price in Yogyakarta in February 1983 was £0.10/kg (£1 = Rp1000). Kerosene, on the other hand, was only £0.075/kg in 1982, increasing to £0.125/kg in January 1983. The higher energy content of kerosene (44 MJ/kg vs 29 MJ/kg) and the higher efficiency of kerosene wick and pressure stoves, compared to charcoal stoves, make it cheaper to use than charcoal. For use in cooking however the bad smell of kerosene, the after taste it leaves, the heavier and more expensive stove it requires, and the inability to use it for grilling, means that there still is a large market for charcoal.

There are a few metal charcoal stoves produced but the vast majority are made of pottery. Charcoal pottery stoves 'anglos' are one of the major products of potters near Yogyakarta. The one piece anglos (Figure 1) sell for £0.075 in the potter's village and for up to £0.15 in a store, for the medium size stove. Under heavy daily use (eg. food vendors, and restaurants) they last less than two months.

In 1980 and 1981 Dian Desa made a number of new prototype charcoal stoves, but whilst they were faster than the traditional anglo they could not be made easily or cheaply by local artisans so no further work was done.

In 1983 Aryanto Soedjarwo and Bill Stewart began some new experiments with charcoal stoves. A simple prototype was made by lining a traditional anglo with cut pumice stone - the most easily available refractory insulation. m e pumice is mined in East Java and is widely available in hardware stores across Java. Its main use is for scrubbing stones, so the pumice available is in the form of 6-10 cm diameter balls. It costs £0.30/kg when purchased in small quantities. The balls were cut with a hacksaw and wedged into the stove to form a layer of insulation -about 5cm thick. The pieces were held in place by a cement mortar. The cement will crack under prolonged heat and a new production procedure is necessary to produce long lasting stoves. For the purpose of the testing this was not a problem. About 300 gm of pumice were used in the stove. Initial tests showed that there was not enough air flow through the grate because the insulation had blocked some of the holes. These holes were bored out to increase the air flow. The following table shows the grate areas for the three stoves tested.

STOVE

Hole Area

Total Grate Area

Holes


sq cm

sq cm

%

Traditional Anglo

27

176

15

Pumice lined Anglo

23

133

17

Thai bucket

8

154

30

Test Procedure

me stoves were filled to capacity - 300 gm for the traditional anglo and Thai bucket, and 250 gm for the pumice lined anglo. A few pieces of charcoal were immersed in 10 gm of kerosene and placed back on the bed of charcoal and lit. Aluminium pots, 25 cm diameter, with lids were filled with 2 litres of water, brought to the boil, and boiled for 30 minutes (BP S30). None of the stoves had doors and all. The stoves were fanned to increase burning rates. Four tests were done on each stove. Results previously reported in Boiling Point No 4, for a traditional Kenyan charcoal stove and a Kenyan charcoal cement-vermiculite stove are shown for comparison (Table on following page).


FIGURE

Test Conclusions

1. The traditional Indonesian ceramic charcoal stove is 20X more thermally efficient than a traditional Kenyan metal charcoal stove. Apart from small differences due to the variations in test conditions, such as quality of charcoal, the improvement in thermal efficiency may be attributed to the higher charcoal bed temperature achieved as a result of the difference in stove wall material, ie metal v. insulating pottery.

2. The pumice-insulated stove consumed less fuel than the traditional ceramic stove. Overall it was 22% more thermally efficient.

3. The Thai bucket consumed slightly more fuel than the traditional ceramic stove, but the evaporation rate was significantly faster. Overall it was 19% more efficient.

4. Given the high cost of charcoal in relation to the stove cost (1.5 kg charcoal costs the same as one stove) a stove that gave significant savings in fuel should be potentially attractive to consumers.


FIGURE


FIGURE

Aprovecho Internships

The Aprovecho Institute has several positions open in its internship programme, and is seeking strongly motivated individuals who demonstrate a commitment to apply learned skills in a Third World setting.

The internship will begin with a month of intensive introductory study into the world firewood crisis, theories of combustion, heat transfer, food transformation in cooking, and fireless cookery, as well as a treatment of working in developing cultures. The remaining 5 months will involve more self-motivated learning including weekly seminars by our staff, daily consultation with specialists, hands-on stove construction projects, and opportunities for individual research and publishing. Instructors will include Ianto Evans and Michael Boutette (co-authors of 'LORENA STOVES').

Instruction will be at the Aprovecho Rural Centre near Cottage Grove, Oregon. Accommodation is available. Interns are encouraged to arrive up to two weeks early to arrange housing and acquaint themselves with the community.

The internship fee is US$ 1, 900 for six months including tuition and residence. In cases where the fee presents a real hardship, Aprovecho can advise on scholarship sources. IF INTERESTED, please write to Aprovecho giving details of yourself and your plans.

Aprovecho Institute, 442 Monroe Street, Eugene, Oregon 97402, USA.

Pottery Stove Production in Sri Lanka, India, and Indonesia

In recent years a great deal of attention has been focused on the use of pottery to make improved fuel efficient stoves. In many countries traditional pottery stoves are widely available in market places and traditional potters and stove designers have made new stoves from pottery because of its low cost, resistance to heat, and flexibility in terms of design and production. Potters in different parts of the world use substantially different techniques in choosing and mixing the raw materials, making objects, and firing them, so it is not possible to define the best way to make a pottery stove. The examples on the following pages, from Sri Lanka, India, and Indonesia illustrate three different methods used by potters who produce hundreds of stoves per month. All the stoves are made for wood and agricultural wastes and have one firebox and two pot-holes.

In all cases there are a number of similarities. me proportion of sand in the clay used for making stoves is higher than in the clay used for making pots to increase thermal shock resistance. Pre-measured sticks instead of judgement are used to check measurements. A mixture of turning, coiling and slab techniques are used. The stoves are made over a period of days with different operations being done on different days. The stoves are fired in the traditional kilns or bonfires. The stoves are installed permanently by encasing them in mud to protect against mechanical and thermal shock.

In each case the method used for making the improved stoves is different from the method for making traditional pottery stoves. However, the new methods are based on the broad range of pottery techniques used and are the result of the interaction of the skills and ideas of the potters and those of the outsiders who introduced the new designs. This process of interaction between the potters and the outside designers must be undertaken if new pottery stoves are to be produced successfully.


FIGURE


FIGURE


FIGURE

Hotel Cookstoves in Mangalore, India

Siddhartha Bhatt Central Power Research Institute, India and S Narvekar, R Kulkarni, & R Sunderesan Karnataka Regional Engineering College, India

INTRODUCTION

It was decided to undertake cookstove studies in hotels because it is easier to bring in new stove technology in the commercial enterprise sector, rather than the domestic cooking sector. A survey was conducted in the Mangalore area. About 45 hotels were visited, and 130-140 stoves were studied in detail. These details, covering stove materials, construction, lifetime, operation, costs and fuel used, are available on request from ITDG or the author. The main findings, problem areas and recommendations for improvement are summarised.

SUMMARY

45% of the hotels surveyed used stoves that were both inefficient and inconvenient to operate. m e conditions of the cooks operating these stoves were harrowing.

35% of the hotels had stoves constructed either by the cooks or by masons. They had in some cases tried to imitate improved designs and in other cases used their own ideas and experience. These stoves did not do much to improve efficiency or overcome pollution problems.

20% of the hotels had built stoves with chimneys, interconnections, fuel feed doors, air regulators, and exhaust hoods, etc. designed to simplify operation and reduce inconvenience, fire hazards, and pollution. In this respect they were superior but were not optimised from the stand point of energy conservation. Their overall efficiencies were low and they wasted most of their heat.

The Figures show a sample of the designs encountered in hotels of this region.


FIGURE

It was not possible to measure the efficiency by conventional tests (eg. PHU) because the owners did not allow intrusions. me owners had an idea of total daily fuel consumption, but not for each stove (no hotel had less than two stoves). m e efficiencies were assessed by noting the temperature rise of water (placed in a pan appropriate to the stove size) for 2 minutes. The input was determined by a rough figure of firewood consumption per day as reported by the operator.

STOVE PROBLEMS

The following sections refer to woodstoves, as these were the majority. The problems of charcoal and husk burning stoves are similar.

Pollution and Inconvenience

Some of the problems found were

1. Stoves were often located at ground level, so that the cooks had to bend down to place and remove vessels, collect ash, control the fire, and feed fuel.

2. No chimney, instead, vessel mounts are used and smoke enters the room causing irritation to eyes and lung problems for operators.

3. Stoves located in rooms so small that there is hardly any circulation of fresh air.

4. Exhaust fans or ventilators are not installed in some hotels.

5. Fuel feed openings too big in most stoves, the radiation causing uncomfortably hot conditions to the workers.

6. Where vessel mounts are used, it also causes uncomfortable heat and releases carbon monoxide.

7. The vessel mounts also result in a greater area of vessel getting exposed to the air cooled flame, causing soot deposition.


FIGURE

Life and Repairs

1. Use of non-fire resistant materials, improperly tamped materials, non-optimum proportions of constituents of bonding materials, lack of sufficient curing of the structure before use.

2. In brick stoves, the life depends to a great extent on whether the bricks are hand- or machine-made, sun- or kiln-dried, laterite or mud. Stoves of machine made firebricks show maximum life.

3. Cement plastering is not desirable because it regularly cracks due to heat.

4. Many stoves are frequently damaged around the pot opening due to the weight of the vessel. Stoves which use iron frames or pottery pieces around the pot openings show reduced frequency of damage.

Performance and Efficiency

Some of the defects which affect the performance are

1. Vessel mounts for exhaust gas outlet reduce efficiency.

2. In stoves with chimneys, these were ill designed with respect to their diameter, length and height.

3. No grates for ash removal, no front dampers for control of air flow rate, and no back dampers for control of fuel burning rate.

4. Height of combustion chamber and log size did not match.

5. Volume of combustion chamber and fuel burning rate not matched.

6. Unnecessarily large fuel feed opening

7. No iron skeleton and hence increased heat transfer to the walls.

8. Pot size and pot opening not matched.

9. Absence of secondary pot openings which utilized the flue gases from the combustion chamber for heating additional vessels.

10. In stoves which had secondary pot openings, the distance between them and the main combustion chamber was too large.

11. Cookstoves in hotels need constant load control, because the rate at which customers come fluctutes and in the absence of such control, the efficiency drops to a low level.

IMPROVED STOVES

Designs of improved stoves must aim at solving some of the above problems.

Optimum System Efficiency

Heat transfer to the vessel is of two types - radiant and convective. In the former there is direct contact between the flame radiation and the pot, while in the latter the flue gases transfer neat to the pan. Both these modes of heat transfer depend on the area of contact and the surface temperature of the heat source. This relationship gives rise to two opportunities for optimisation

1. Maximise the surface area, ie the area of contact between the vessel and the flame, or between the vessel and the flue gas,

2. Adjust the height between the vessel bottom and log top to such a value that the heat transfer is maximum.

Devices for Improving Performance

1. Baffles to direct the flow of hot exhaust gases.

2. Dampers to vary the burning rate by the control of air flow at the inlet, outlet, and intermediate points. Dampers also prevent radiation losses from the front.

3. Chimneys to vent away the exhaust gases and also induce draught which aids combustion.

4. Grates to remove ash from the combustion zone, to improve combustion efficiency, pre-heat air drawn from below, minimise bottom radiation losses, and keep the flame at the central part of the combustion chamber.

5. Use of hand operated blowers to further increase the fuel burning rate at times when excess heat is needed.

6. A metallic lining improves the performance of cookstoves (1). The lining increases the combustion chamber temperature by virtue of the air gap (bad heat conductor) between the lining and the stove wall.

References:

(1) Jayaraman S 'Notes on High Efficiency Wood Burning Stove' 1982, Central Power Research Inst. Bangalore 560012, India

Mud: Rice Husk Stoves of Indonesia

Aryanto Soedjarwo
Dian Desa, Yogyakarta, Indonesia

In some parts of Indonesia a unique type of cooking stove is made of a mixture of mud and rice husks and has the following advantages.

1. It can be made from locally available resources in rice-growing areas.

2. A knife is the only tool needed for construction.

3. The stoves can be built in the kitchen or at a workshop and then transported.

4. The stoves last up to five years before they disintegrate, and can be moved around the kitchen even after a few year's use.

5. me material is strong enough so that it could be adapted to a wide variety of stove designs.

The typical stove seen is a boxlike structure with two potholes with the door in line with the potholes. The second pot is raised so that smoke can escape at the back of the stove. There are no tunnels, baffles or dampers.

Construction

The basic method of construction is the same for building one stove or many stoves, the differences are in the type of moulds used and the drying process. Larger stoves than the one illustrated can be made with the same method.


FIGURE

First a sandy clay that does not shrink much when it dries is mixed with rice husk (2:1 by volume). The clay is usually dug up from the rice paddies and the rice husks are collected from homes or small rice mills. A lot of water is added so the mix has the consistency of very wet mud mortar. One stove will require about 30 kg of wet mix. The mix is left to rot for about one week, by which time it has quite a strong odors. During this 'maturing' the clay particles have been broken down into smaller clay particles and more bonds have been created so the mix is stronger and more plastic. Without this the stove would crumble within a month.

The next step is to place the internal firebox mould, made of pre-cut wood pieces, banana stems, or some other filler, where the stove is to be built. Mud is packed around the sides and the rear.

After one day's drying, the mud for the top is laid on top of the form. Small bamboo pieces to support the arch sections are used in the owner-built method to prevent sagging, because the banana stems are not as stiff as the wooden mould. The potholes are roughly shaped at this time. The walls and top are about 7 cm thick. As the stove dries small cracks appear. These are removed by gently beating the stove with a coconut frond or a bunch of small branches so that the clay spreads out and closes the cracks. After one or two more days the form work is removed and the stove continues to dry. In the kitchens it dries in place, but in larger scale operations they are often made outside and the stoves are dried like bricks. They are dried flat, on one end and then on the other to promote even drying.


FIGURE

These stoves are strong enough and light enough (15 to 20 kg) to be carried by hand or even strapped to bicycles. In Indonesian villages these stoves can be bought for the equivalent of a day's pay for a rural worker, which means about

hours of semi-skilled labour was needed. These stoves are strong and often support pots weighing 10kg. Within a year a crack develops directly down the middle of the stove but it does not greatly impair the performance or strength.

The design could be improved by adding a baffle underneath the second pot-hole and reducing the size of the door and connecting tunnel. This would make it similar to the pottery Tungku Sae stove, which has saved about 40% compared to mud: rice husk stoves in a pilot village in central Java. However, the mud: rice husk stoves do save fuel and are more convenient than some other stoves as the following example shows.

An example of the Diffusion of the Mud : Rice Husk Stove in Indonesia

Indonesia consists of over 10,000 islands and migration from densely populated islands to lesser populated islands is common practice. In one area of south Sumatra a family from central Java brought their stove building skills with them and set up a small family industry to supply the mud: rice husk stoves to other migrants. They produce about 150 stoves every month throughout the dry season which amounts to nearly one thousand stoves per year. Without any outside assistance this family has been able to sell thousands of these stoves which are an improvement over the traditional stove since people are buying them. A traditional technology transferred via skilled craftsmen is proving to be a more efficient method of diffusion than most centrally controlled attempts at improved stove dissemination.

Improved Stoves in India

A Mandal and Dr Rajendra Prasad Indian Institute of Technology, New Delhi

Introduction

The following is taken from an article titled 'An Efficient Smokeless Wood Burning Stove'.

Efforts to improve the traditional methods of cooking over open fires began, in India, about a quarter of a century ago.

In 1953, Hyderabad Engineering Research Laboratories (HERL) designed a chulah which was a major improvement. This chulah is claimed to be extensively used and to save 40% of firewood compared to an open fire.

The Magan Chulah was developed in 1947 at Maganwadi, Wardha. The design accommodated the pot seats on the stove top so that their centres formed an equivalent triangle and utilised an indirect fire channel to the chimney.

In collaboration with the Research and Action Institute, Lucknow, NBO improved the Junagarh chulah whose efficency was reported as 24-72%.

The U P Water Development Corporation modified the Junagarh Chulah and though the height was found to be too low, several chulahs installed in a village worked satisfactorily.

The Gujrat chulah is a modified version of the HERL chulah. The Mada chulah design is based on the Lorena stove from Guatemala, and is being propagated in villages near Chandigarh under a Ford Foundation scheme.

Other smokeless stoves developed or being introduced in India are the Ghana, the New Nepali, and the Kathmandu chulahs.

Based on the results of these chulahs, and on experiments on open fires, a new chulah has been designed and tested at I I T. (Fig 1). The outer appearance is similar to the chulah developed at Jai Nigam, UP, though the dimensions are different and selected on the basis of experiments carried out at II T. It is a two pot chula and is made using moulds. Moulds have been introduced for constructing the firebox as well as the second pot-hole, and small pieces of cement pipes are used for providing the flue tunnels between the firebox and second pot-hole as well as between the pot-hole and chimney. At this moment wooden moulds are used, but several other materials can be tried. The moulds are shown in Fig 2. The chulah has a cement pipe chimney of 7.5 cm diameter with a smoke vent at the top. Between the second pot-hole and the chimney a heat controlling device - a cement damper - is provided to control the flue gases.


FIGURE

Another damper is provided in front of the fire box to control air inlet. The burning rate of fuel can be affected by suitable adjustment of the dampers. With the proper use of dampers more heat is available. The efficiency obtained is about 24%.

A major break through is the extremely simple technique of construction, which can be done to the exact dimensions required with no special skills or training needed.

This new chulah has been constructed in more than 15 houses in a labour colony near I I T. The chulah is highly acceptable to the poor people. They can clearly see a saving in their fuel. The new chulah gives an additional pot seat to cook on and at the same time saves the cook from smoke.

Chimneys

The installation of chimney stoves to remove smoke from houses has been one of the major objectives of many stove programmes.

Chimney stoves have advantages and disadvantages over non-chimney stoves. The main advantage is the reduction of pollutants in the kitchen. Chimneys can assist to ignite and burn low quality and wet fuels. In Nepal, chimney stoves are used successfully to burn maize and rice stalks.

Chimney stoves usually cost more than non-chimney stoves for the initial purchase, and there are greater recurrent costs. They also take longer to install. Low mass mud and ceramic stoves, with chimneys, provide less room heat since the flue gas cannot easily warm the room. It is more difficult to make use of the flue gas for drying the roof, crops, or fuelwood, unless a short chimney is used (ie an indoor chimney), or the pots are removed and the smoke allowed to escape through the pot-hole(s).

Unless chimneys are cleaned regularly the performance of the stove will decrease as the chimney blocks up and there is the possibility that tar formed in the chimney will ignite. This applies especially when agricultural residues are burnt.

Chimneys must be installed correctly otherwise they will not draw properly. Incorrectly installed chimneys can result in roofs (especially thatch) catching fire.

Chimney caps must also be carefully designed, and the chimney placed on the leeward side of the house if wind is not to blow down the chimney (ie backdraughts are to be avoided).

Children may easily block chimneys with dirt or stones if the exit is not protected, or placed out of reach.

It requires more effort to train people to install chimney stoves, and more intensive monitoring to ensure the quality of installation is maintained.

Hints on Designing and Installing Chimneys

1. Never make a chimney with a diameter of less than 10 cm and a height of 1 metre (for further details see Technical Notes No 2 'The Optimisation of Chimney Stoves', issued with BP No 4).

2. Make sure that a chimney is 1.5 metre below a ceiling or overhang (if placed indoors) or 0.5 metres above a roof (Figure 1). Never install a chimney under a thatch roof (Figure 2) as it could catch fire.

3. When putting a metal chimney through a flammable roof, install a sheet metal thimble, (Figure 3).

4. Always make provision for easy maintenance of the chimney. This can be achieved by

- leaving a 10cm well at the bottom of the chimney (Figure 4) so soot does not block the exit passage from the stove

- providing access at the base to remove the soot

- sloping the stove exit passage down so that soot can be easily pushed into the well

- regularly tapping the chimney to knock loose soot into the well

- if the chimney is taken out through the wall, providing a cap (Figure 5) at the bend to make cleaning easier.

5. Install a chimney cap as illustrated in Figure 6 if local conditions (eg prevailing winds) will cause backdraught problems.


FIGURE

Book Reviews

'RICE HUSKS AS A FUEL' Sekam Padi Sebagi Baha Baka
by Craig Thorburn, 1982

76pp, US $3.50 plus US $1.50 postage and packing.

This unique bilingual (English and Indonesian) book gives tried and true examples from Indonesia, Thailand and the Philippines of how to use rice husks for home cooking, hotels, food processing, brick and tile firing and even banana ripening.

All of the 17 processes described were developed by local people, drawing on their accumulated expertise which often represented appropriate solutions to needs in specific geographic, social and economic environments. Besides describing the different stoves and firing techniques the book illustrates the tools and techniques in sufficient detail so that they can be copied or altered to meet local conditions and needs. For anyone living or working in rice growing areas, this book will be of great value.

'TEKNOLOGI KAMPUNGAN : A COLLECTION OF INDIGENOUS INDONESIAN TECHNOLOGIES'

by Craig Thorburn, 1982

154 pp. US$ 5.00 plus US$ 2.00 postage and packing.

Using a similar approach to 'Rice Husks as a Fuel' Craig Thorburn has documented over 100 technologies from agriculture, fishing, post harvest processing, cooking utensils, water supply, transportation, architecture, small industries, and the informal sector. Not just a collection of drawings, it goes into great depth about the operations surrounding the technologies. The section on pottery cooking stoves should be of special interest to people working with stoves and nearly everyone will find some useful ideas in this excellent book.

Both books are available from the Appropriate Technology Project, Volunteers in Asia, PO Box 4543, Stanford, California 94305, USA.



FIGURE

ITDG Stoves Project Recent Publications


One or both of the following publications are being circulated with this issue of Boiling Point to certain of our readers.

'THE SARVODAYA STOVES PROJECT : A CRITICAL REVIEW OF DEVELOPMENTS 1979 - 82'

by M Howes, S Joseph, Y Shanahan, W Stewart and H Navaratne.

ITDG has been closely associated with the stove programme run by Sarvodaya in Sri Lanka. Bill Stewart was involved from the start of the programme as a VIA volunteer, before becoming the ITDG field officer and spending a large part of his time in Sri Lanka. Stephen Joseph and Yvonne Shanahan have also made several visits to Sri Lanka over this period to assist in all aspects of the programme, from testing and stove production, to monitoring and evaluation.


'A COMPUTER MODEL TO EXAMINE THE EFFECT OF COOKING METHOD ON THERMAL COMFORT LEVEL' by Stephen Joseph and Jeff Kenna.

It is claimed that massive mud stoves, once they have heated up, actually keep the house or kitchen warmer than an open fire. This claim has yet to be substantiated scientifically.

This computer model (in BASIC, suitable for microcomputers) was commissioned with two aims - to enable the determination of the likely change in comfort levels which would occur if a new stove was introduced; and to determine the room and radiant temperature experienced in the environment of an open fire, and of the following types of stove - massive mud, small mud and small ceramic.

Those who would like a copy should write to the ITDG Stove Project (address on front cover) and send £ 1.00* (for the Sarvodaya report) or £ 1.50* (for the computer model) to cover postage and packing.

* or US$ equivalent at current rate of exchange. Preferred payment by International Money or Postal Order.