<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""> Crispin cc stoves (being added back in)</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>1. Let me try again. I said: "<i class="">How about picking two pages/equations here that you think has been done incorrectly? (No more than 2, please, at first.)” (from the site and the attachment).</i></div><div class=""><span class="Apple-tab-span" style="font-style: italic; white-space: pre;"> </span>I presume many on this list were waiting to see what you disliked the most in this sort-of official “bible”.</div><div class=""><i class=""><span class="Apple-tab-span" style="white-space:pre"> </span></i></div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>2. We agree on one thing. I have been arguing against the subtraction in the denominator (described below) for at least a decade. Not for your reason though. That approach under- (not over-) estimates the efficiency I want reported. (Not in your analysis below, because you threw away part of the char that I was trying to obtain - char of the size you want to forget about is “exactly” ready for the garden.)</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>3. Maybe we will agree if you show us your calculation of the various Inefficiencies (emphasis only on the “in” part) in your example. Where exactly do you see “wasted” or “non-useful” energy?</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>4. I’d rather not have hundreds of us waste time looking up the “<span style="font-style: italic; color: rgb(31, 73, 125); font-family: Calibri, 'Slate Pro', sans-serif, sans-serif; font-size: initial; text-align: initial; background-color: rgb(255, 255, 255);" class="">dreadful 2016 paper from BUCT and Kirk Smith</span><font color="#1f497d" face="Calibri, Slate Pro, sans-serif, sans-serif" size="3" class=""><i class="">” , </i>even though I am willing<i class="">. </i> Could you supply that cite please?</font></div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>5. To repeat, for emphasis, I am looking for specifics in the 2014 version of the “bible”. Especially the part about not reporting weights.</div><div class=""><br class=""></div><div class="">Ron</div><div class=""><br class=""></div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 25, 2016, at 12:42 PM, Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@outlook.com" class="">crispinpigott@outlook.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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Dear Ron</div>
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<span style="font-size:initial; text-align:initial; line-height:initial" class="">Thanks for the well-phrased questions. </span></div>
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No char-making stove I have seen has a high fuel efficiency. </div>
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The reason I personally brought the new Nurhuda stove to the group instead of waiting for him to say something is because of the relevance of the double-fuel design to the reporting of the fuel efficiency metric. </div>
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The metric for fuel consumption relates to the energy in it and what happens to it. The delivered energy, cooking or space heating or water heated in a low pressure boiler is the 'delivered energy'. That is the numerator of the efficiency metric. Energy contained
in char produced is not 'delivered', it is retained in the remnant solid fuel. Char is definitely 'produced' but the energy it contains is not. It was already there. </div>
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The energy in the fuel fed into the system needed to deliver the benefit (cooking or whatever) is the number in the denominator. The result is the efficiency expressed as a fraction or % if you wish:</div>
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<span style="font-size:initial; text-align:initial; line-height:initial" class="">Work done/input energy = efficiency</span></div>
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The error in the WBT is to deduct something from the denominator. This was never correct. The fuel fed is the fuel fed, not something less. Char produced as a co-benefit goes in the top line, not deducted from the bottom. </div>
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The efficiency of Nurhuda's stove is the same calculation done twice in sequence. That is, the efficiency as a char maker, then the efficiency as a char burned, then the combination. </div>
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If one chooses not to burn the char, the fuel consumption of the first operation is not 'increased' as a result.</div>
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As a practical example, the same in principle as I provided a few years ago, is:</div>
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Wood energy into Nurhuda's char maker with the larger fuel chamber: 10 MJ worth of wood pellets. </div>
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Delivered energy to the pot, 3.5 MJ</div>
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Efficiency 3.5/10=35%. </div>
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<span style="font-size:initial; line-height:initial; text-align:initial" class="">Char recovered after cooking: 4 MJ worth of char pellets. </span></div>
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<span style="font-size:initial; line-height:initial; text-align:initial" class="">Char energy not recovered due to its being too small and dispersed, 1.0 MJ which is a mechanical loss. </span></div>
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Char loaded into the small chamber and lit to continue cooking: 4 MJ worth of charred pellets. </div>
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Delivered energy to the pot, 2 MJ. </div>
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Efficiency, 2/4=50%. </div>
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As I have mentioned many times before, running two incompatible cooking operations means the efficiencies cannot be averaged directly because the denominators are different. Basic rule of math. This is another error in the WBT but I will ignore that for now. </div>
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The efficiency of the system evaluated as a 'pair of burns' is the total energy delivered divided by the total energy entering the system. </div>
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Session 1 energy gained plus Session 2 energy gained divided by the total energy going in. This treats the entire sequence as a single cooking event. </div>
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(3.5+2)/10 =55%</div>
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The fuel efficiency (which I prefer to call the energy efficiency in line with other devices) of the char making cooking operation is 35%, not 55%. The WBT reports the efficiency of Session 1 as </div>
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<span style="font-size:initial; text-align:initial; line-height:initial" class="">3.5/(10-4)= 58.3%.</span></div>
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I just checked to be sure. It is incorrect, obviously. 58.3 is more than 35.</div>
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The WBT would rate Session 2 as being perhaps 60% efficient, assuming there is some char left, for a total of 118.3% of the original energy, or some other crazy construct. </div>
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I believe in Christmas miracles but not that one. The reason it is so wrong is because of the double counting and the irregular subtraction from the denominator. </div>
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The error in the WBT formula is to deduct something from the denominator, is that now clear?</div>
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The efficiency of cooking in the Session 1 is 35%. The efficiency of retaining recoverable char energy during that session is 40%. The efficiency of cooking in the second event is 50%. All three of these results are determined by a number in the numerator.
That is how to calculate efficiencies. </div>
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At no time does one subtract a delivered energy value from the denominator. Suppose you measured the space heating energy and the cooking energy at the same time. Suppose the energy gained was the same for each: 3.5 MJ. The cooking efficiency is </div>
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3.5/10=35%</div>
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The space heating efficiency is </div>
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3.5/10=35%</div>
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The cooking efficiency is NOT found by dividing the 3.5 MJ delivered to the pot by (the energy in the fuel supplied minus the space heating energy). That would be ridiculous. Space heating is a co-benefit.</div>
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If the cooking was done inside the heated space, then the total delivered space heating energy is (3.5+3.5)/10=70%. </div>
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If you treat recoverable char as a co-benefit, it is considered in the numerator. It is not subtracted from the denominator. Char has well known properties of mass and specific energy content. It's production efficiency (however you assess the portion of it
as 'recoverable') is mass of char per unit of dry mass of fuel fed in. In the example above the yield I used is 20%. The specific energy content I assigned was 30 MJ/kg.</div>
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So Dr Nurhuda's new stove can be assessed as a char making cooking stove, or as a char maker, or as a char making, char burning stove treating the entire session as a single cooking event. All three are legitimate and the above formulas are what one needs to
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The highest efficiency I have seen for a char making stove is in the low 40's and the mass of char recovered is about 20% of the dry fuel mass fed in. </div>
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Incidentally, just to save time, the phrase 'energy credit for char' can be applied to these formulas. It goes in the top line, and is not subtracted from the bottom because the mass or energy of the char does not reduce the mass of raw fuel consumed. You could
create a 'cooking plus char energy' efficiency. Nothing wrong with that though it would be non-standard. Doing so would not raise the cooking efficiency, however. </div>
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You could also have a 'cooking plus space heating' efficiency. Perfectly legitimate, but adding in the space heating efficiency would not increase the cooking efficiency either. </div>
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Finally, if you wanted to know the <i class="">heat transfer efficiency</i><span class=""> as per that dreadful 2016 paper from BUCT and Kirk Smith, that is an internal metric referring to something happening within the stove and any similarity to the energy efficiency is purely
coincidental. Usually they are not similar for solid fuel stoves. The heat transfer efficiency for a char making stove is often twice the value of the energy efficiency. </span></div>
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Regards </div>
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Crispin </div>
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<div class="">Crispin and cc list:</div>
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<div class=""><span class="x_Apple-tab-span" style="white-space:pre"></span>I have just skimmed through a very lengthy document (found at: <a href="http://cleancookstoves.org/technology-and-fuels/testing/protocols.html" class="">http://cleancookstoves.org/technology-and-fuels/testing/protocols.html</a>) that
includes (the latest, 2014?) WBT protocols: </div>
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<div class=""><span class="x_Apple-tab-span" style="white-space:pre"></span>I presume you are still unhappy that this document gives a report that shows a TLUD making char can have a high efficiency?</div>
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<div class=""><span class="x_Apple-tab-span" style="white-space:pre"></span>I find the weight of the fuel being prominent - so don’t understand your statement below on this topic. How about picking two pages/equations here that you think has been done incorrectly?
(No more than 2, please, at first.)</div>
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<div class="">Ron </div>
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<div class="">On Dec 25, 2016, at 7:32 AM, Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@outlook.com" class="">crispinpigott@outlook.com</a>> wrote:</div>
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Dear Andrew </div>
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I wasn't implying either density or mental lethargy! I was really asking if the gravity of the implications of making flippant claims about stove 'impact' are apparent and accepted. </div>
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For ten years now, as confirmed by Dean Still, I have been raising a rukus about the multiple conceptual and mathematical errors still contained in the WBT. The gravity and implications have been widely accepted
<i class="">outside</i><span class=""> the immediate community of old timers but only minor corrections have been accepted in, particularly, the US-based stove community. By that, I mean ANSI, Aprovecho, Berkeley, Colorado, EPA, GACC. The ABCEG. </span></div>
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<span class="">Why this resistance to simple facts? There are very real, harmful consequences to this hide-boundedness. The current call for refugee stoves by the UN, to be shipped in batches of 10,000, demands they be tested using the WBT (the tender document
links to multiple versions of it) and the first criterion is 'E' which they believe is 'fuel efficiency', as in, the fuel consumed during the test. The WBT doesn't report the fuel consumed during the test! Nowhere on the form is there a place to enter the
mass of fuel consumed to perform the test. It lies. The tender document also specifies that the test used must be able to replicate results within 1/3 of the tier span, then calls for 'tier 4' performance. The WBT they insist on cannot replicate results within
that spec! It can't do it with 10 tests, nor 20, nor 100, so I am reliably told. There is no way a WBT can place a stove on tier 4 as any field test will show. </span></div>
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<span class="">This failure is being reported in paper after paper. Someone spending a lot of money is going to notice. The stove developing and promoting community is facing a loss of credibility of Clintonesque proportion. Many other organisations are going
to experience similar credibility problems once the gravity of the misrepresentations of the 'health impact' are grasped by those who are paying for these stoves. </span></div>
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<span class="">To make progress we have to have clear guidelines on how to create valid performance tests and potential impact claims, hence my questions put to Nikhil. It is becoming clear what we cannot claim. We should set a clear path to a believable future. </span></div>
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<span class="">Regards </span></div>
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<span class="">Crispin </span></div>
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<br class="">
<div id="x__originalContent" class="" style="">On 24 December 2016 at 23:30, Crispin Pemberton-Pigott<br class="">
<<a href="mailto:crispinpigott@outlook.com" class="">crispinpigott@outlook.com</a>> wrote:<br class="">
<br class="">
><br class="">
> I hope this is sinking in, not just for you but for the stove community in<br class="">
> general.<br class="">
<br class="">
I don't know about sinking in, perhaps I'm slow on the uptake or dense?<br class="">
<br class="">
I do think it's a meaningful discussion<br class="">
<br class="">
Andrew<br class="">
<br class="">
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