[Stoves] How to convert thermal efficiency into fuel savings figures

[ajheggie at gmail.com]

[Default] On Wed, 10 Oct 2012 12:02:41 -0500,Paul Anderson
<psanders at ilstu.edu> wrote:

>Dear Stovers,
>
>I do not know how to convert thermal efficiency into fuel savings figures.
>
>I hope it Is a linear transformation.     10% TE wastes 90% of fuel, 
>while 40% TE wastes only 60%?    But I suspect it is more complicated 
>than that.
>

I hope Kevin's answer didn't confuse you as much as it confused me!

If we take the efficiency figures as being correct and that they are a
measure  of how much of the fuel energy liberated is delivered into
the pot then a 15% efficient 3 stone fire will burn 3.7 times as much
fuel to do the job compared with a very good stove with 55%
efficiency.

At these higher levels of efficiency the heat exchange interface with
the pot will be more significant then the completeness of combustion.

Given that the mass flow through  the stove and above the pot should
be the same then a quick calculation using the temperature just above
the flame and at the exit from the pot will give a relative figure for
heat exchange; the ratio of heat supplied to heat rejected. Note at
higher efficiencies this will decrease more noticeably as the pot gets
hot because heat transfers to the pot depends on delta T between the
hot gas and the pot contents.

AJH