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<DIV><FONT face=Arial>Dear Marc</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=marcpare0@me.com href="mailto:marcpare0@me.com">Marc-Antoine Pare</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">Discussion of biomass cooking
stoves</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Cc:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">Discussion of biomass cooking
stoves</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, October 11, 2012 2:13
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] How to convert
thermal efficiency into fuelsavingsfigures</DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>Kirk Smith's "Short Primer on Stove Efficiencies" was the best
explanation of "efficiency" as it relates to stoves that's have encountered.
And only 2 pages!</DIV>
<DIV><A
href="http://stoves.bioenergylists.org/stovesdoc/Smith/Primer/Primer.html">http://stoves.bioenergylists.org/stovesdoc/Smith/Primer/Primer.html</A><BR></DIV>
<DIV><FONT face=Arial># Paul is trying to relate stove efficiencies to
savings. This paper does not help him much in that regard. This Paper
basically </FONT><FONT face=Arial>seems to be saying is that the
"...stove design and combustion efficiency are not as important as heat
transfer to the pot... to make a better stove, find better ways to get
the heat out of the hot gases and into the pot..."</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial># The definition of "Nominal Combustion
Efficiency" is not a good one, in that it does not recognize the importance of
"stack loss" resulting from excess air. </FONT></DIV></BLOCKQUOTE>
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<DIV>Careful in comparing stoves of different classes -- TLUD "efficiency" can
mean something quite different from Rocket "efficiency". For example: what do
you do with the leftover char? It probably depends on where in the world
you're talking about (even with the same stove!)</DIV>
<DIV> </DIV>
<DIV><FONT face=Arial># In the case where it is intended that the stove
function primarily as a "Cooking or Space Heating" stove, then the production
of charcoal as "unburned carbon in the ash" is a dead loss, and will result in
a very low "Stove Efficiency." On the other hand, if it is desired for the
stove to produce charcoal, (for use as fuel elsewhere, or for use as biochar),
then it is quite fair and rational to deduct it's energy content from the
energy content of the input biomass, when calculating "stove efficiency."
</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial># Equally, if a "space Heating stove" was also used for
cooking, its loss of heat to the living space is benefit, and not a loss, or
an inefficiency.To calculate the efficiency of such a stove system (ie,
cooking and heating), one could simply do a stack gas analysis, and knowing
the temperature of the stack gases, one could easily calculate a meaningful
efficiency. On the other hand, if shell loss from the stove was not desired
for space heating, then this method would not be relevant, in that it cannot
distinguish between the fraction of input energy doing "useful work" (cooking)
compared to the fraction that is wasted through the stove walls.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial># Stove efficiency, for stoves intended for use in the
tropics where the "heat leakage" is not desired or beneficial, can be improved
by reducing the "shell loss" with insulation.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Best wishes,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Kevin</FONT></DIV>
<DIV><BR></DIV>
<DIV>-Marc </DIV>
<DIV><BR>On Oct 11, 2012, at 9:13 PM, Kevin <<A
href="mailto:kchisholm@ca.inter.net">kchisholm@ca.inter.net</A>>
wrote:<BR><BR></DIV>
<DIV></DIV>
<BLOCKQUOTE type="cite">
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<DIV><FONT face=Arial>Dear Andrew</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>----- Original Message ----- </FONT>
<DIV><FONT face=Arial>From: <</FONT><A
href="mailto:ajheggie@gmail.com"><FONT
face=Arial>ajheggie@gmail.com</FONT></A><FONT face=Arial>></FONT></DIV>
<DIV><FONT face=Arial>To: "Discussion of biomass cooking stoves"
<</FONT><A href="mailto:stoves@lists.bioenergylists.org"><FONT
face=Arial>stoves@lists.bioenergylists.org</FONT></A><FONT
face=Arial>></FONT></DIV>
<DIV><FONT face=Arial>Sent: Thursday, October 11, 2012 5:02 AM</FONT></DIV>
<DIV><FONT face=Arial>Subject: Re: [Stoves] How to convert thermal
efficiency into fuel savingsfigures</FONT></DIV></DIV>
<DIV><FONT face=Arial><BR></FONT></DIV>
<DIV><FONT face=Arial>> [Default] On Wed, 10 Oct 2012 12:02:41 -0500,Paul
Anderson<BR>> <</FONT><A href="mailto:psanders@ilstu.edu"><FONT
face=Arial>psanders@ilstu.edu</FONT></A><FONT face=Arial>> wrote:<BR>>
<BR>>>Dear Stovers,<BR>>><BR>>>I do not know how to
convert thermal efficiency into fuel savings
figures.<BR>>><BR>>>I hope it Is a linear
transformation. 10% TE wastes 90% of fuel,
<BR>>>while 40% TE wastes only 60%? But I suspect it
is more complicated <BR>>>than that.<BR>>><BR>> <BR>> I
hope Kevin's answer didn't confuse you as much as it confused
me!</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT size=4 face=Arial># My apologies for a confusing explanation. If
you could point out where my explanation was confusing, I will attempt to
clarify.</FONT></DIV><FONT size=4 face=Arial></FONT>
<DIV><BR><FONT face=Arial>> <BR>> If we take the efficiency figures as
being correct and that they are a<BR>> measure of how much of the
fuel energy liberated is delivered into<BR>> the pot then a 15% efficient
3 stone fire will burn 3.7 times as much<BR>> fuel to do the job compared
with a very good stove with 55%<BR>> efficiency.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=4># That is only true in the limited cases
where the stated efficiencies are correct, and where there is no benefit
from the heat that does not actually enter the pot. If I burn wood in a
stove to heat my cabin, what is the stove efficiency, if I do not have a pot
on the stove making stew?...</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>---> Is it 0% Efficient because I
have no pot to measure its heat gain?...</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>---> Does it suddenly attain
some degree of efficiency if I set a pot of something on it to
cook?</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=4># Consider the example of Rocket Stoves,
and TLUD's venting into the living space, and a box stove with a
chimney that vented the products outside the living space, that are used in
different applications:</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>1: a thatched hut in a Tropical Jungle
Setting, </FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>versus</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>2: an application (eg, in Mongolia
or Northern Canada requiring both space heating and cooking capabilities),
where the same stove is used for both space heating and cooking.
</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>compared to</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4>3: A box stove, intended for both space
heating and cooking, having a chimney that vented outside the living
space.</FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT size=4></FONT></FONT> </DIV>
<DIV><FONT size=4 face=Arial># In comparison of Case2 and Case
3, the Rocket stove would probably show much better pot boiling rates
than the box stove, but total system efficiency and annual fuel savings
would probably be far greater with the box stove. We don't see Rocket Stoves
or TLUD's that vent their products of combustion into the living space being
used for space heating applications in temperate or cold climates, because
the need for excess ventilation will require much greater fuel quantities to
heat the cold fresh replacement air required for health and safety. In Case
1, a TLUD may win over a Rocket, in the instance where the person
wanted to make a quick pot of coffee, but the Rocket may win, in
the instance of where the person wanted to simmer a pot of stew for 1
hour.</FONT><FONT face=Arial><BR>> <BR>> At these higher levels of
efficiency the heat exchange interface with<BR>> the pot will be more
significant then the completeness of combustion.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=4># How are these "levels of efficiency"
actually attained? Are the real benefits of "heat loss to the room"
included, when relevant? </FONT><BR>> <BR>> Given that the mass flow
through the stove and above the pot should<BR>> be the same then a
quick calculation using the temperature just above<BR>> the flame and at
the exit from the pot will give a relative figure for<BR>> heat exchange;
the ratio of heat supplied to heat rejected. Note at<BR>> higher
efficiencies this will decrease more noticeably as the pot gets<BR>> hot
because heat transfers to the pot depends on delta T between the<BR>> hot
gas and the pot contents.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=4># This is not really "stove efficiency",
but rather, it is more like a determination of "efficiency of coupling
between a heat source and a heat sink." It is like drawing a graph with a
suppressed zero... a picture is painted but it is not necessarily the
correct, meaningful, or important picture. </FONT></FONT></DIV>
<DIV><FONT size=4 face=Arial></FONT> </DIV>
<DIV><FONT size=4 face=Arial># My fundamental concern is that stated stove
"Efficiencies" and "Savings" can be very misleading and are prone
to being used out of context. The only way to get a fair and true comparison
of efficiencies is to do a "Mass and Energy Balance" on situations that do
indeed have a true basis for comparison. "Good figures never lie, but Good
Liars often figure. ;-)</FONT></DIV>
<DIV><FONT size=4 face=Arial></FONT> </DIV>
<DIV><FONT size=4 face=Arial>Best wishes,</FONT></DIV>
<DIV><FONT size=4 face=Arial></FONT> </DIV>
<DIV><FONT size=4 face=Arial>Kevin</FONT></DIV>
<DIV><FONT face=Arial><FONT size=4></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT size=4></FONT></FONT> </DIV><FONT
face=Arial></FONT>
<DIV><FONT face=Arial><BR>> <BR>> AJH<BR>> <BR>>
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