[Stoves] [Ethos] Additional presentations at ETHOS 2015

[T Hastings]

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> 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]
> 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
>
>
> _______________________________________________
> Stoves mailing list
>
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>