[Stoves] Examples of results of simmer efficiency Re: [Ethos] Additional presentations at ETHOS 2015

Sat Feb 14 16:17:28 CST 2015

Dear Crispin,

I see the stove with higher heat transfer efficiency using less energy to
accomplish the same task. It will not have evaporated more water when both
stoves simmer the water at 97 C. The stove with poorer heat transfer
efficiency will use more fuel to do the same task and will have a lower
score. The important ability is Turn Down Ratio.

Best,

Dean

On Sat, Feb 14, 2015 at 11:52 AM, Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:

> Dean, consider two stoves that are exactly the same in every way except
> that one is slightly higher in heat transfer efficiency.
>
> They are operated in exactly the same manner ‎and start the simmer with
> exactly the same amount of water in the pot. They have exactly the same
> fire in them with exactly the same emissions.
>
> The only difference between them is that at the end, the more efficient
> stove will have evaporated more from the pot because it has a slightly
> higher heat transfer efficiency.
>
> Now calculate the output: Specific fuel consumption.
>
> Energy used of mass of fuel - you choose.
>
> Divide it (it is the same for both stoves) by the number of litres in the
> pots. The more efficient stove will have a higher specific fuel consumption
> because, and directly a result, of its HIGHER performance. So a designer,
> we're they to use this metric, would be led to believe, much against the
> reality that the more efficient stove is better, that it is fact worse than
> the other one.
>
> What could be a more useless metric than one that tells the designer they
> made. 'worse' stove when they have just improved it?
>
> In 2004 you wrote a brief paper on this very subject, explaining that a
> negative result for a better stove meant there was something wrong with the
> protocol. Well, the problem is still there in v4.2.3.
>
> There are several things wrong:
>
> The concept of 'water simmered' is defective because the volume changes
> constantly.
>
> The use of the final ‎mass is based on the concept that a 'better stove'
> will evaporate less water, contra-indicated by the above example.
>
> The simultaneous calculation if the 'thermal efficiency' ‎rewards the
> stove that evaporates more water as 'better'  even as the SFC punishes that
> same stove for being 'worse'.
>
> It is worse and better at the same time! How does that help the designer
> or tester?
>
> To get a "better result' the operator should raise the water to a boil
> with as little evaporation as possible so as to start off with the largest
> amount possible, so the water remaining is the largest possible so the
> divisor is as big as possible so the final SFC number is as small as
> possible.
>
> As the fuel needed to keep the pot only depends on the heat losses from
> the pot‎, not how much water is in it, the 'clever cook' beats the test -
> cheats as Sam calls it - and gets a better rating even if the stove is
> worse.
>
> Three stoves which produce exactly the same ‎mass of PM but which have
> different heat transfer efficiencies cannot receive three different PM/MJ
> (NET) ratings. The 'heat gained (MJ(NET)) is measured by the amount of
> water that is evaporated from the pot when simmering, even though there is
> no requirement to evaporate anything. Turning down the stove, as you
> suggest, to score high on the SFC metric, greatly increases the PM mass per
> MJ of heat that supposedly gets into the the pot.
>
> The entire low power section of the IWA, and now that the WBT has been
> modified to match it, is junk science. There is no other word for it. It
> stoves are variously rewarded and punished and rewarded and punished in a
> random manner that does not tell us which one is 'better', there is no use
> for the numbers.
>
> The whole purpose of my motivating for the creation of a Working Group
> specifically for conceptual review, metrics and definitions was to put an
> end to the flawed and error-riddled tests that were 'a good idea at the
> time' in 1985 but which have been shown to be lamentably defective.
>
> That 14 countries out of the 15 that voted for the creation of WG1 is a
> statement that such a thoroughgoing review is urgently needed. You can
> prepare and bring your numbers but you should bear in mind that the global
> stove community is moving on from the WBT. It does not and cannot serve our
> purposes.
>
> As Paul was at pains to point out, I don't think anyone had bad intentions
> - in the entire stove community - but we cannot pretend that the WBT is
> making legitimate calculations based on valid concepts.
>
> ‎The three low power metrics are invalid. The variables selected are
> inappropriately chosen. The calculated results are misleading and contrary
> to any claim they provide guidance for product development or selection. We
> have to move on.
>
> Regards
> Crispin
>   *From: *Dean Still
> *Sent: *Sunday, February 15, 2015 02:08
> *To: *Discussion of biomass cooking stoves
> *Reply To: *Discussion of biomass cooking stoves
> *Subject: *Re: [Stoves] Examples of results of simmer efficiency Re:
> [Ethos] Additional presentations at ETHOS 2015
>
> Dear Paul,
>
> To do well on the Low Power Specific Consumption metrics the stove has to
> have a good Turn Down Ratio. In other words, the stove has to have high
> power and low power.
>
> Specific Consumption is based on how much energy was used to create
> simmered water. If the stove only operates at high power there is more
> steam made and less simmered water remains so energy was used to create
> less product.
>
> I like Specific Consumption because it forces stove designers to make
> stoves that simmer successfully, not just boil water. For example, new
> TLUDs are better stoves because they have both high power and low power. In
> my opinion, the WBT 4.2.3 helped to create these more successful TLUDs.
>
> As Sam says, we are working on a paper showing characteristics of the WBT
> 4.2.3 for the ISO work. Knowing the characteristics lets folks evolve a
> perfect test.
>
> Sam is doing great work as he crunches all the data and gives ISO real
> numbers to work with in their discussions.
>
> Best,
>
> Dean
>
> On Sat, Feb 14, 2015 at 8:18 AM, Paul Anderson <psanders at ilstu.edu> wrote:
>
>>  Dear Tom H.,         and to all who are interested in proper testing of
>> stoves.
>>
>> Your reply about your experiences is helpful.   Sounds like you had
>> qualified testing center do the testing, in accordance with the procedures
>> that Crispin is questioning.   Please send to me the full details.   Could
>> be off-list, but this is sufficiently important that we will want the full
>> results known.
>>
>> I have a specific case of official testing of one of my stoves with
>> unfavorable results for Low-Heat Efficiency (simmering).   I will add that
>> into the list of examples and provide the details very soon.
>>
>> I invite anyone else who has something to report about simmering
>> efficiency to also send details of their experiences, either favorable or
>> unfavorable or neutral.
>>
>> The examination of the questionable methods about simmer efficiency might
>> take some days, maybe weeks.   But not the months or years that this debate
>> has been "simmering".
>>
>> Remember:  A testing center that properly conducts testing using an
>> endorsed but possibly flawed procedure is NOT a culprit.  The culprit is
>> the testing protocols, *IF found to be faulty.   *And we hope that the
>> testing center people (employees and leaders) who understand the technical
>> aspects of the calculations will be among those who can help resolve these
>> serious issues.
>>
>> Even those who developed protocols that are eventually shown to be faulty
>> are not culprits.   Mistakes can be made.    However, the culprits can
>> include those who advocate a protocol that he or she knows (or reasonably
>> suspects) to be faulty.
>>
>> Paul
>>
>> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
>> Email:  psanders at ilstu.edu
>> Skype: paultlud      Phone: +1-309-452-7072
>> Website:  www.drtlud.com
>>
>> On 2/14/2015 3:04 AM, T Hastings wrote:
>>
>> Hi Crispin (and all list members),
>>
>> Thanks for explaining the low fuel consumption Tier 4 rating of my own
>> tests on the Unity Charcoal Stove. In the simmer phase I used only a
>> tiny amount of fuel to maintain the simmer. With the pot pretty well
>> inside the stove and the EVA foam lid on the pot their would have been
>> little heat loss to the environment. Also the walls of the stove would
>> have been hot from the high power tests and radiating heat back to the
>> pot. I can see that virtually any other stoves that incorporate
>> insulated pot skirts would have the same results. It is pretty much as
>> you explained it with removing the pot and putting it away, then
>> continuing to maintain a minimum fire. (Its a bit more convenient for
>> the user if it stays on the stove of course!)
>>
>> Mind you, whilst it may be gaming, insulating the pot it is actually
>> achieving a lower fuel consumption and tangible benefits to the end
>> user. It helps in high power and low power tests.
>>
>> Anyway I do agree that having a flawed standard is of no help to
>> anyone. I hope that the new ISO standard will correct that.
>>
>> Best Regards
>>
>> Thomas Hastings
>> Unity Stove
>>
>>
>>
>> On Sat, Feb 14, 2015 at 3:26 PM, Crispin Pemberton-Pigott<crispinpigott at outlook.com> <crispinpigott at outlook.com> wrote:
>>
>>  Dear Sam
>>
>> Thanks for posting the presentation "How to Cheat on the WBT" addressing the
>> issue of low power performance measurement.
>>
>> The core of the problem is not that changing the mass of water changes the
>> result of the calculation, giving a different rating for the performance on
>> that metric. That was always true.
>>
>> The root problem is that metric 'Specific Fuel Consumption' for low power is
>> not valid in the first place. Please see
>>
>> KEY DIFFERENCES OF PERFORMANCE TEST PROTOCOLS FOR HOUSEHOLD BIOMASS
>> COOKSTOVES, Yixiang Zhang, Crispin Pemberton-Pigott, Zongxi Zhang, Hongyan
>> Ding, Yuguang Zhou, Renjie Dong
>>
>> DOI:10.1109/DUE.2014.6827753
>>
>> It is one of the issues discussed.
>>
>> It is remarkable to me that this has not been comprehensively addressed by
>> the US teams in the current environment of trying to improve the usefulness
>> of stove test results.  During the development of WBT 4.x the matter was
>> stonewalled, to everyone's disadvantage.
>>
>> Before we get into the details of the mathematics or the gaming of a stove
>> test, the metric has to have validity in the first place. It doesn't.
>>
>> Why?  Because there is no relationship between the heat needed to keep a hot
>> pot hot and the mass of water contained in it. Was explored at Eindhoven in
>> the early 80's. The SFC was rejected also by Rani et al in 1991, again in
>> 2014 by Zhang et al. Zhang's experiment was reproduced by Jim Jetter last
>> year re-confirming that the mass of water has no influence in the amount of
>> fuel needed. What value can there be in dividing one number by the other?
>> Why not divide by 8 instead?
>>
>> Accepting these multiple experiments, it is conceptually obvious that
>> changing the mass of water used to divide into the mass of fuel consumed (or
>> the energy number) renders the result meaningless.  Not 'less useful',
>> 'meaningless'.  Zhang's experiment just did the experiment very accurately
>> (four 9's). The Indians did it quickly and pointed out that it supported the
>> conceptual analysis that low power specific fuel consumption was not a
>> useful metric because it didn't tell us anything.
>>
>> Thank you for bring this to the attention of ETHOS. It has far-reaching
>> implications.
>>
>> All three of the low power metrics in the IWA are have no physical basis and
>> therefore have no value for predicting anything. Part of the inherent 30%
>> variability in the WBT is caused by the use of poorly conceived metrics that
>> report 'numbers'. One of the motivations for the creation of Working Group 1
>> under ISO TC-285 was to assure the use of correctly grounded metrics 'with
>> value' for regulation and performance rating.
>>
>> Debating how to influence the result of a SFC low power number is like
>> debating what colour to paint the hull of the Titanic.  The problem is that
>> of trying to assign an engineering performance number - energy per unit work
>> done - to a task that does not require the accomplishment of work - keeping
>> a pot hot.
>>
>> Consider this. When the simmering phase starts, take the pot off and put it
>> into a well-made retained heat cooker in the next room.  Keep the fire going
>> in the stove. Measure the emissions. After 45 minutes, divide the mass of
>> fuel used for the fire (or the energy released or anything else you want) by
>> the number of litres in the pot in the other room which is still hot, of
>> course. Do the same with another stove.  Compare the results. What have you
>> learned?
>>
>> The emissions from the stove are unaffected by the amount of water in the
>> pot sitting in the retained heat cooker. If it was still on the stove
>> instead of in the RHC, the number of litres would still not affect the pot's
>> 'need for heat'. The only 'need' is to overcome losses. Those losses are not
>> measured. Remaining hot is the only prescribed task.
>>
>> If the RTC is extremely well insulated, the heat loss would be zero. That
>> means the efficiency of a perfect simmer (which is what a perfect RCT
>> represents) is, according, according to the WBT, 0%.  The better the stove
>> and the more controllable and the fire, the lower the calculated final SFC
>> number. This shows the silliness of the metric.  A better result is supposed
>> to result in a better rating not a worse one. Where that number is on 'tier
>> 4' is meaningless.
>>
>> 'Simmering' is a task. 'Specific Fuel Consumption' is an energy efficiency
>> metric. They are not compatible. Calling it Low Power (as happened at the
>> IWA after the obvious was rejected) does not make it relevant to performance
>> rating. I hope you can convince some of your peers. This matter is
>> distracting us from far more important topics.
>>
>> Best regards
>> Crispin
>>
>>
>> -----Original Message-----
>> From: ethos-bounces at vrac.iastate.edu [mailto:ethos-bounces at vrac.iastate.edu <ethos-bounces at vrac.iastate.edu>]
>> On Behalf Of Samuel Bentson
>> Sent: Saturday, February 14, 2015 06:49
>> To: Anderson
>> Cc: ethos at vrac.iastate.edu; marchese at colostate.edu; Discussion of biomass
>> cooking stoves
>> Subject: Re: [Ethos] [Stoves] Additional presentations at ETHOS 2015
>>
>> Hi Paul,
>>
>> I chose that title to garner interest. It worked! The point is to show how
>> to better standardize the WBT, and in case that is not possible, to show how
>> to be aware of how the results can be manipulated or misunderstood. Here are
>> the slides I threw together in a few minutes after deciding not to do my
>> original talk. It's mainly just some headings. We're working on a paper that
>> goes into detail about the water quantity used, it also talks about the
>> temperature of the water during simmer, and the firepower used to bring the
>> water to boil.  You're right that the quantity of water influences the
>> emissions metrics. The current WBT does have some language about not
>> comparing tests that were conducted with different amounts of water, but it
>> is vague. I wasn't aware of it when I gave the talk and I don't think other
>> testers I have spoken to are aware of it.
>>
>> Sam
>>
>>
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