[Stoves] Efficiency of clean fuel

[Crispin Pemberton-Pigott]

Dear AJ and Philip

>....what you are measuring is the 
>heat supplied to the pot less the heat lost out of the sides of the 
>pot at 100C. If the same pot and routine is used then a comparison 
>can be made between fuels.

I describe this as the determination of thermal efficiency the way a boiler
is tested. Quite legitimate.  I do like to add that it should be tested at
different power levels because it can vary a great deal.  As the gas
velocity drops (assuming reasonable control over excess air) the efficiency
can rise by more than double as the gas residence time increases. I have
seen mid-70's with a paraffin stove.

I have been thinking of adding such a test to the coal stove test in UB.
Apart from the three dimensions I mentioned: combustion efficiency, stack
losses and emissions per kg burned, people do cook on the stoves so a
cooking efficiency test is warranted. Again it can be at different power
levels.

I have to be careful in reviewing tests that people are not comparing stoves
with water heating included in the 'efficiency' with those with no water
heating included.  My late friend and math advisor David Garcia says that in
mathematics this is termed 'cheating'.

Regards
Crispin

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