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close this bookBoiling Point No. 19 - August 1989 (ITDG - ITDG, 1989, 36 p.)
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View the document‘Efficiency' Of Wood Stoves
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‘Efficiency' Of Wood Stoves

by F W Hottenroth of the ZZ Corporation, California

Lord Kelvin, an expert on heating and cooling, said: "When you can measure what you are talking about, you know something about the subject. Until that time your knowledge is of a meager and unsatisfactory nature."

Can the efficiency of stoves be measured precisely? Can the efficiency measurements of one stove be used to compare it to another stove? Are the standards for measurement adequate and the procedures clearly established?

Efficiency of electric, gas and kerosene stoves can be measured with reasonable accuracy. Test results can be used to compare one stove to another. This is not true in regard to wood burning stoves. Unlike other stoves, the efficiency of a wood burning stove depends greatly upon the way it is used.

A two pot stove may have a high potential efficiency when used with two pots each of which contains a specified amount of food, but the actual efficiency, under field conditions, will be much lower if only one pot hole is used by the family for much of its cooking.

It is important that the potential efficiency be determined as accurately as possible under clearly established standard conditions. The basic procedures set up by VITA and others for measuring efficiency of wood stoves are a good start. However, it seems important that the standards for measurement clearly spell out the dimensions and material of the pots to be used during the test and the quantity of water to be boiled.

Tests at ZZ Corp are made with a small pot and with a large pot. Results are comparable to field usage with small meals and large meals. Figure A shows an aluminium pot suitable for most cooking of small meals or sauces. The large pot is 23.0 cm x 30.5 cm x 1.5 mm thick. In the small pot, 4 litres of water are brought to aboil, and 12 litres in the large pot. Pots with these dimensions are readily available. We suggest they be used as standard.

Testing at ZZ Corp, is used mostly to compare one ZMART ZTOVE to another to evaluate the effect of proposed changes. Efficiency measurements of acceptable accuracy are obtained using a straightforward procedure to obtain the data to be filled in on a data sheet.

* There is no organization in the wood stove industry to promote standards. We urge the formation of a suitable society to coordinate the technical aspects of the industry with membership open to those in the industry who have suitable technical backgrounds.

Two organizations which have international prominence and competence in the wood stove industry are ITDG and the Wood Stove Group at Eindhoven University. Either of these or another equivalent organization could sponsor a technical society and foster its growth. The society could pull the woodstove industry together and restrain it from galloping off in all directions. Establishment of efficiency standards should be a top priority but there are many additional areas which would benefit from the coordinated planning of its cooperative members.

* This is the view of the contributor, a US engineer with long experience of stove work. They are not the views of the ITDG stove programme. What do you think?