[Stoves] Differences in stove testing ---- was Re: ETHOS 2017 agenda and logistics

[Ronal W. Larson]

List and Crispin:

	The short quotation below won’t be clear to those not following this debate closely.  It is from my reply message at 9:58 on 31 Jan to Paul Anderson - in which I went a lot further reporting on the test experts I talked to at ETHOS - NONE of whom agreed with Crispin on the topic of this reply - the way to handle char in reporting efficiencies.  The “John” in this message is EPA’s John Mitchell, who I feel I can now quote as agreeing with my interpretation below.  John Mitchell supports the existing “denominator equation” - as does EVERYBODY I talked to at the ETHOS conference.  See a small qualifier in this 31 Jan message on misuse of the results - but those experts still did not find fault with the equation itself.
.
	Inserts below.


> On Feb 4, 2017, at 9:07 AM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> 
> Dear Ron
>  
> “When you report John saying “the testing protocols are now with some adjustments for char-producing and for ash-producing stoves”, this means that the efficiency number that Crispin prefers (zero credit for charcoal production; do not use the “denominator equation”) is there as well as the one that you and I prefer - which gives partial credit to char production - via this same “denominator equation”).”
>  
>  
> I think you should be very clear about what you want:
>  
> You want to increase the cooking efficiency metric number by deducting the energy content of the recovered char energy, is that correct?

	[RWL1:  I am agreeing with decades of usage to make the “cooking efficiency metric number" more accurate.  The ONLY accurate denominator is one with the char being subtracted - as the ratio is the heat into the cook pot divided by the total energy that COULD BE available for that measure of energy into the cookpot.  Energy that is in the char was NOT available to go into the cookpot.  It HAS to be subtracted to get a valid efficiency when you are running different tests with relatively arbitrary and unintentional amounts of char being produced.

	You are the only person I have heard say this is improper.  Your view has been dismissed by dozens of others - especially in “official”polling.

	I think the “denominator equation” formula undervalues (not overvalues) the energy in the char.  It says the inefficiency is larger than it is.  I accept  the formula only because the tier structure is based on its use.  I would have been happier with a tier structure based on overall efficiency, but I know that is impractical - especially at this late date.

>  
> This deduction raises the reported fuel efficiency.
	[RWL:  For small amounts of char it makes the reported efficiency more accurate.  It undervalues the overall (more than heat transfer) efficiency of stoves that are trying to make char.

>  
> Are you OK with that as the result?
	[RWL:  Marginally.   Only in the tier heat rating sense.
	
	Example:   If energy into the boiling water and charcoal each are one-third, then the sum of all inefficiencies MUST also be one-third.  You argue for a heat transfer efficiency of 1/3 (dropping all consideration of the char).  The “denominator equation” (used by everyone but yourself as near as I can determine) says the “heat transfer efficiency” is  (1/3)/(1-1/3) = (1/3) / (2/3) = 1/2.    I can live with this, but I also think it important to say that the inefficiency is NOT also 1/2.  The overall efficiency, when one is trying to produce char, is 1/3 +1/3 = 2/3.  This last is clearly NOT the “heat transfer efficiency”, but the overall efficiency should be reported as well if we are trying to promote more valuable stoves, and it is not being reported.

	Now the reverse question -  WHY are YOU so unhappy with the subtraction in the denominator?  Is it your opinion that this char production was an inefficiency?    You have expressed great unhappiness with the “denominator equation”, but I don’t recall ever seeing a reason.  The purpose of including a char term in the denominator is NOT to say anything about char - it is to get at the POTENTIAL heat transfer efficiency.  To repeat - too many will think that char-making stoves are much less efficient than they really are.

Ron

>  
> Thanks for clarifying
> Crispin
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