 | Boiling Point No. 04 - March 1983 |
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Focus on Testing
In December 1982 a meeting of stove testers from Asia, Africa, Latin and North America, Europe and Australia (Stephen Joseph!), was held in Washington at the head offices of VITA (Volunteers in Technical Assistance). The purpose of this meeting was to draw up a recommended procedure for the field testing of stoves (in draft form). The meeting was highly successful - agreement was reached on a procedure and a draft publication is being produced by VITA. Participants agreed to test this procedure over the next year and determine what changes may be necessary in the light of experience.
Discussions with the staff of Cookstove News are underway to produce a joint edition on testing methodology and practice.
In the last three months we have received two reports on testing, and a summary of these follows.
I COMPARATIVE WOOD CONSUMPTION IN 'IMPROVED' COOKSTOVES
by Stephen Connors, Peace Corps, Lenin
Stephen Connors (in Lenin, West Africa), carried out controlled boiling water tests on a 3-rock fire, a locally produced metal stove, a modified version of this metal stove (with sand insulation), and a SOTA stove (see REVIEWS).
The test procedure used was that described in Tim Wood's paper 'Laboratory and Field Testing of Improved Woodstoves in Upper Volta'.
The PHU values calculated from the test results were compared with those from tests carried out by Wood on an open fire and on four stoves built in the Upper Volta. He found that when compared with the 3-rock fire, the three stoves from Benin and the four stoves from Upper Volta show a decrease in wood consumption greater than 30%, and an increase of PHU of 40%. However, if the same comparison was made between the existing metal stove in Lenin and the other 'improved' stoves, only two of the latter, one from Benin (SOTA) and one from Upper Volta (CATRU-A) showed a decrease in fuel consumption of 20% or more, and an increase in PHU greater than 20%. Given that the CATRU-A costs over $30, and the existing Benin metal stove costs $1, he questions whether this is a viable alternative.
FIGURE
He concludes that it is necessary to consider not only wood fuel savings, but also economic and social factors when designing a stove.
II CHARCOAL STOVES AND THE POSSIBILITIES FOR IMPROVING THEIR EFFICIENCIES
by Michael Drohan, University of Bradford
Mr Drohan's report is of some of the work carried out at Kenyatta University College, Nairobi, as part of a research project on the efficiencies of charcoal stoves.
Two separate sets of experiments were carried out, on 8 charcoal stoves, using slightly different methods. Five stoves were tested using the first method, and one of these five (the traditional Kenyan jiko) and the remaining three stoves were tested using the second method. The two sets of results for the traditional Kenyan jiko therefore provided a comparison between the two methods.
In the first set of experiments, cooking conditions were simulated by using a fairly standard aluminium pot (diameter 25 cm) and a fairly standard cooking load of 3 litres of water. me water was heated from room temperature (approximately 20ºC) to 85ºC and was then discarded and replaced by a fresh lot of water. (The water was decanted at 85ºC to avoid complexities arising from high evaporative losses as boiling point is approached.) This process was continued until the charcoal load ceased to yield a rise in temperature of the water in the pot. The accumulated temperature rise multiplied by the mass of water and by its specific heat, was reckoned as heat effective in cooking. Heat used in raising the temperature of the pot was reckoned as heat losses together with convection and radiation losses from the sides of the stove and the pot.
For the second method a 40 litre container was constructed on the top of an ordinary aluminium cooking pot so that a normal load of charcoal (0.75 kg) would raise the temperature of its contents to between 70ºC and 80ºC. The reservoir built on the cooking pot was insulated with fibre-glass wool and covered with a coating of diatomite, leaving only the surface of the cooking pot uninsulated as in normal cooking conditions. The temperature was measured automatically by means of a thermistor, the output of which was fed into an operational amplifier and an electronic recorder.
The author points out that convection and radiation losses from the sides of the container would be much higher under normal conditions of cooking (as the pot contents would be brought to the boil, and then simmered or kept boiling more vigorously), but the experiments were designed to demonstrate the relative performance of various designs of stoves.
The heat of combustion of a sample of the charcoal used in the experiments was determined and the efficiencies of the stoves calculated from the heat outputs found in the tests. m e results below are taken from the report.
"Absolute Efficiencies of Various Charcoal Stoves"
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STOVE |
METHOD |
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First |
Second |
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Traditional Kenyan Jiko |
20.5% |
21.9% |
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Bellerive Model I |
18.0% |
-- |
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Bellerive Model II |
20.7% |
-- |
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Variant of Bell. Model I |
19.6% |
-- |
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Schmalzle Stove |
28.5% |
-- |
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Traditional stove with brick lining |
-- |
27.4% |
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Traditional stove with clay lining |
-- |
29.2% |
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Thai Bucket Stove |
-- |
34.2% |
The author concludes:
"The research and testing here reported revealed that modifications to existing charcoal braziers have produced improvements of the order of 50% on the existing ones without considerably increasing the cost of the stove. If universally adopted for charcoal burning, this technology could reduce the consumption of charcoal by one third. m us from the energy point of view, without consideration of afforestation and reforestation strategies, and more efficient methods of charcoal production, improvement in stove technology could make a considerable contribution to conservation of renewable energy resources. However, as pointed out at the beginning of this paper, this is only the technical dimension of the problem of renewable energy conservation and as such is incomplete without an analysis of the political economy of renewable energy."
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