[Stoves] The need to continue the discussion Re: simmer efficiency

[Crispin Pemberton-Pigott]

 Dear Dean

It will be interesting to have people comment on what metrics show ‎that a stove is better, then to run some theoretical stoves through the calculations to see if 'better' is shown in the result. That is my test of the test.

I do not think we are moving a consensus forward. There is strong disagreement between the supporters of the old VITA-style metrics and those who long ago realised the are not mathematically defensible. All the low power metrics of the IWA are invalid because they express the answer in terms of the mass of water in the pot. The mass of water in the pot has no bearing on the performance of the variable being measured. Therefore there is no point in dividing the measurement by the number of litres in the pot, either the final number or the initial number as has recently been done with the WBT (check too see).

Using the initial water mass gives a number that is irrelevant to the performance. Using the final number as a divisor gives an even wronger answer. ‎Liking it does not validate it.

The target of 1.75 mg/min indoors is a number that can easily be achieved by putting a ‎chimney on the stove. The WHO assumes the smoke is emitted into the room. They are incorrect. In many places people cook mostly outdoors or under a shelter. There are no walls in many kitchens.

The WHO assumes there are walls and models the exposure assuming the PM is well mixed in that ‎room. KK Prasad showed 30 years ago that this assumption is quite incorrect. Smoke is NOT well mixed and assuming it is gives a very incorrect exposure result compared with measuring the exposure in a real kitchen. I have no faith in their model. It certainly is not applicable to almost all of Africa, India, Indonesia and south east Asia, which is about 2.2 billion people.

Next, the WHO assumes that if a chimney is used, 25% of the smoke will be emitted indoors which is ridiculous - there is no other word for it. I questioned the motive for making such a silly assumption on this list a few weeks ago.  ‎In short, they have no plan to measure emissions, they will assume that any chimney stove leaks 25% of the PM into the room and that it gets well mixed, thus overcoming the physics of chimneys and air mixing thermodynamics all at the same time.

Suppose you achieve the emission rate. For what size of stove? People use maybe 5 stove sizes here in Yogyakarta. From 1.5 to 25 kW. The WHO does not accommodate this reality with a fixed limit of 1.75. Even if the number is realistic, is it a practical approach?

The IWA at least recognised this issue and set an emission rate per useful amount of work done. For the high power tests it is at least a valid concept.

My interpretation of the WHO emission rate is that they are using a linear exposure and disease consequence model‎, itself difficult to justify, and an atypical room, and an unreasonable assumption that the obvious solution of adding a chimney 'won't work' (according to the document) because 25% of the emissions will be assumed to stay indoors. The conclusion reached is that only electric cooking and LPG should be allowed because everything else too smoky. That assumption is then used to rule out the use of all solid fuel for cooking at some point in the future.

It sounds like it was written by the LPG industry because everyone knows that electric cooking is many decades away for most people.

The strangest aspect of the WHO method is that they do not intend to ‎to measure actual exposure to emitted substances. Just the model. That is like modelling the emissions from a fire instead of measuring them. I mean, why build testing labs?

Good luck with making great stoves. Meeting the target is not impossible I think.

The Mini-Dul TLUD in Mongolia emitted 7.3 mg/delivered MJ which is 99% less than the baseline. That is quite a bit more than 1.75 mg/minute, but none of it entered the home. It has a chimney.

It is about half the PM allowed/MJ(net) in a 'tier 4 stove' when cooking. I can't compare for the Low Power because mg/min/litre is not a valid metric so we don't use it.

But the exposure of the cook to PM is zero.

The stove with the code PCB1-P was tested at YDD in September. It scores 10.3 mg/MJ(net) at a firepower of 2.4 kW. That translates to ‎0.76 mg/min at its average heat transfer efficiency of  ‎51.2%.

It happens that it meets the Tier 4 target (emits 1/4 of what is permitted) and meets the WHO emission rate with less than half what is permitted. Running at its peak PM efficiency (2.0 kW) ‎it emits 1/17th of the amount it emits on average which is 1.5% of what is permitted at Tier 4. The heat transfer efficiency in that condition is just over 60%. Pretty good competition, I'd say.

If they can do it, I am sure others can.

‎Greetings
Crispin


Dear Paul,

Crispin began this weekend of exchanges by talking about two stoves.

The stove with better heat transfer efficiency causes more water to be
boiled off in a simmering test.

So, he asks, is the "better" stove penalized?

No, says the ISO IWA metrics, only having better heat transfer efficiency
does not make a  "better" stove.

The IWA definition of a "better" stove also includes having a good Turn
Down Ratio.

When the better stove with both better heat transfer efficiency and better
Turn Down Ratio is tested

 it uses less wood than the stove with poorer heat transfer efficiency. It
keeps the water at a set temperature (say 97 C) using less energy.

New TLUDs can do this! Congratulations! Progress!

Older TLUDS had fantastic heat transfer efficiency but couldn't turn down
so well. The rice is burned, etc.

New TLUDs can boil at high power and simmer at low power. Less burned rice.


It's Monday morning and I'll try to summarize what I think is going on with
the simmering test.

Please remember that at least 30 experts in testing are volunteering
together to evolve by consensus a new ISO test for stoves.

No one is getting paid. It's an interesting mathematical problem.

Sam and I are crunching data from over 100 stove tests to give this big ISO
committee data.

The eventual test may be like the Chinese or Indian tests. The committee is
looking at everything.

Sam and I think that the Low Power simmering portion of the WBT 4.2.3 needs
to have a standard pot with a standard amount of water.

We think that the computer used with the emissions hood can track the water
temperature every couple of seconds.

Mathematically, at the end of the simmering test, the wood use would be
corrected as if the water had been maintained at a set temperature (say 97
C).


Water Boiling Tests are simple and complicated. (A great math problem)

These lively debates are part of the consensus process that slowly moves
toward shared truth.

As I said, Sam and I are writing up our findings and we'll post them here
as well as sending them to ISO.

I'm getting back to work trying to make a stove that meets another very new
standard by the World Health Organization:

Less than 1.75 mg/minute of PM 2.5.

Is this the new international test (mg/min)?

Best,

Dean



On Mon, Feb 16, 2015 at 2:01 AM, Paul Anderson <psanders at ilstu.edu> wrote:

>  Dear Philip and all,
>
> Thank you.   You have done something that was needed.   Your comments
> should be studied by everyone.   I am in agreement with you.   My goal is
> for ME to understand it sufficiently.   And you have helped greatly.
>
> My comments:
> 1.  For doing the work of Bringing to Boil, the MJ/(minimum Liters) can be
> seen as appropriate.
>
> 2.  But for the task of simmering (which is without work, or with "no
> increase in enthalpy"), the calculation of Specific Fuel Consumption (SFC)
> does not make sense.  Wikipedia tells me that:
>
> Enthalpy change accounts for energy transferred to the environment at
> constant pressure through expansion or heating.
>
> At first it looks like the heat (such as from a strong fire) that goes
> into the pot needs to be counted.   BUT that heat then exits the pot in the
> form of latent heat in the evaporated water.   Therefore, there is a net
> "no gain" in heat in the pot, hence no work or no increase in enthalpy.
>
> I hope I got that reasonably right.   Feel free to correct me.
>
> I hope that all readers feel free to agree or disagree with Philip.
> Please do not depend on me to get the questions clarified.   I would expect
> that someone who advocates the WBT usage of SFC for low power calculations
> will make a response.
>
> 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 2/16/2015 1:15 AM, Philip Lloyd wrote:
>
>  Dear Paul et al
>
>
>
> I said the simmering test was FUNDAMENTALLY wrong.  When something is
> fundamental, it is not something for which you need “time for discussion.”
> So let me explain the fundamental problem:
>
> 1.      To quote the definition “Specific Fuel Consumption  – This is a
> measure of the amount of fuel required to boil (or simmer) 1 liter of
> water. It is calculated by the equivalent dry fuel used minus the energy in
> the remaining charcoal, divided by the liters of water remaining at the end
> of the test. In this way, the fuel used to produce a useful liter of “food”
> and essentially the time taken to do so is accounted for.
>
> Specific Fuel Consumption is listed as the IWA metric for Low Power, which
> is reported in MJ/(min·L)”
>
> 2.      At constant temperature - the simmering temperature – there is no
> increase in the enthalpy of the water in the pot.
>
> 3.      All energy used is therefore used to make good [the] energy lost
> from the pot by radiation, convection and conduction, and to supply the
> heat required to evaporate some water. The last of these losses is
> determined by the surface area of the liquid in the pot and the lid
> tightness or otherwise.
>
> 4.      None of these heat losses is determined by the volume of water in
> the pot.
>
> 5.      As a result, the fuel consumption does not depend on the volume
> of water in the pot, and the “Specific Fuel Consumption” likewise is not
> determined by the volume of water in the pot, only by the geometry of the
> pot, the material of which it is made, and the tightness of the lid.
>
>
>
> If you can indicate to me which of these points is in error, I will be
> happy to debate that point, but until you can do so, I must maintain that
> the metric, and therefore the test, is *fundamentally* wrong.
>
>
>
> The thought experiment is to pour all the contents of the pot, once it has
> reached 3 degrees below local boiling, into a thermos flask. It will
> “simmer” (remain -3 to -6 degrees below boiling) for a long time and
> require no heat input at all. A “hot box” similarly is effective because
> the food is cooked with no external heat input. Neither the thermos nor the
> hot box efficiency depends on the volume of liquid, only on the
> effectiveness of the insulation.
>
>
>
> Over to you.
>
>
>
> Philip
>
>
>
> *From:* Stoves [mailto:stoves-bounces at lists.bioenergylists.org
> <stoves-bounces at lists.bioenergylists.org>] *On Behalf Of *Paul Anderson
> *Sent:* 16 February 2015 06:47
> *To:* Discussion of biomass cooking stoves
> *Subject:* [Stoves] The need to continue the discussion Re: simmer
> efficiency
>
>
>
> Dear Philip,      and to Dean and all,
>
> Philip wrote:
>
> I do not think we should waste much more time arguing about them – they
> are fundamentally wrong.
>
> It is precisely because things are (or might be) wrong that we need this
> time for discussion, even if it is a form of arguing.   To not press for
> clarification (and a possible reversal) of what Dean is so staunchly
> defending would be to yield to the status quo of the testing procedures.
>
> Crispin has been rather lonely as the outspoken critic of the status quo
> WBT.   It is interesting to hear such a solid support by you (Philip).
> It would be good to hear from others who agree with Crispin's comment:
>
>  The variables selected [for Low Power testing] are inappropriately
> chosen. ....
>
> But Crispin and you give an incorrect comment when saying:
>
>  ....  We have to move on.”
>
> The time is NOW to keep this discussion going until there is resolution.
> It might take a while, but as I see it, there are at least two CAMPS or
> lines of thinking about the Low Power measurements in the stove testing.
> Dean seems to present much of the thinking found in the USA, with some (but
> probably not all) supporters in the GACC and EPA.   Crispin suggests that
> at least some other countries and agencies are supportive of his line of
> reasoning (China, Indonesia, South Africa, World Bank).   But certainly
> that also is not 100% locked in.
>
> Perhaps there is a totally different method or two.   Perhaps the current
> method and an alternative are BOTH meaningful.   But I doubt that.   I am a
> stove designer, not an equation-using physical-chemical scientist.   So I
> will win when whichever testing methodology is found to be correct.   And I
> am VERY CONCERNED that in 2015 we still need this discussion and debate.
> But it must be resolved!!!!!!!!!!!
>
> Dean commented (and I think I did not take it out of context):
>
>  ... the new approaches are forged by consensus.
>
> "Consensus" will prevail (and there will be some who will never join the
> consensus).   But consensus is not to be based on democratic votes or even
> a slight majority number of nations adopting some set of standards.   What
> must prevail is the SCIENCE associated with the testing procedures.
>
> We should not be here trying to get votes like politicians.   We need to
> be hear sound scientific arguments.   So, my requests are:
>
> Philip, (and others) please help explain what is incorrect with the Low
> Power testing measurements and calculations.   Most specifically, the use
> of a variable called "amount of water boiled away during simmering" seems
> to be in question.  (also expressed as weight of water in pot at end of
> simmering time).
>
> Dean, (and others) please help explain how the boiling away of water
> during simmer time *has meaning in the calculations* .   We understand
> that evaporated water represents heat energy that exits the system.   But
> the system is about maintaining a boiling point (or slightly below), and
> that task is accomplished whether the evaporation is of 0 or 100 or 300 or
> 500 or more grams of water.
>
> AND we know the amount of fuel that was consumed.   What is important is
> the fuel consumption, and we do not need "weight of evaporated water " to
> know the fuel consumption.   There is no "work" in simmering except to keep
> the water in the pot from going below the minimum allowed temperature.
> And the water temperature cannot possibly go above the boiling point
> (unless in a pressurized vessel, which is not an allowed consideration).
>
> To all:  Please help us all to see the formulae (three of them, for
> efficiency, CO and PM) that are in the current version of the testing
> protocol.   The document is public and on the Internet.   Please help us
> find the right specific pages.    I will not pretend to understand such
> formulae, but with help, I want to boil it down to the issue of the
> evaporated water.  Does it matter?   Should it matter?
>
> I am most focused on the formula for efficiency, but all three with
> survive or fall together with the understanding of the impact of the amount
> of water that is evaporated during simmering.
>
> This is NOT the time to turn away from this discussion.
>
> 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 2/15/2015 1:43 PM, Philip Lloyd wrote:
>
> Dear Dean
>
>
>
> Crispin said it well:
> “The three low power metrics are invalid. The variables selected are
> inappropriately chosen. The calculated results are misleading and contrary
> to any claim [that] they provide guidance for product development or
> selection. We have to move on.”
>
>
>
> I have looked at the simmering metrics in WBT 4.3.2 and can only concur.
> That is why I do not think we should waste much more time arguing about
> them – they are fundamentally wrong. Yes, stove designers need to be
> concerned with simmering and turndown; no, the WBT simmering metrics do not
> provide them with guidance, and can be positively misleading, which is
> worse.
>
>
>
> Kind regards
>
>
>
> Philip Lloyd
>
>
>
>
>
> *From:* Stoves [mailto:stoves-bounces at lists.bioenergylists.org
> <stoves-bounces at lists.bioenergylists.org>] *On Behalf Of *Dean Still
> *Sent:* 15 February 2015 06:38
> *To:* Discussion of biomass cooking stoves
> *Subject:* Re: [Stoves] Examples of results of simmer efficiency Re:
> [Ethos] Additional presentations at ETHOS 2015
>
>
>
> Dear Prof Loyd,
>
>
>
> As I pointed out, when the stoves do the same work (hold the water at 97
> C, for example) the stove with greater heat transfer efficiency scores
> better. Simmering tests are important and simmering is an important part of
> cooking.
>
>
>
> The ISO process is creating new history and approaches to old problems.
> Whatever emerges will certainly be defensible as the new approaches are
> forged by consensus.
>
>
>
> Best,
>
>
>
> Dean
>
>
>
> On Sun, Feb 15, 2015 at 12:58 AM, Philip Lloyd <plloyd at mweb.co.za> wrote:
>
> I am concerned that this is turning into a very fruitless discussion.
>
>
>
> On fundamental grounds the simmering test does not provide anything
> meaningful.  Crispin has demonstrated that rigorously, and others have
> pointed out that the test can score an efficient stove poorly and an
> inefficient stove well, so it does not provide any useful measure.  To go
> on defending the indefensible does not make sense, even if it did
> accentuate the need for turndown – but that need was always there, it was
> not the product of the WBT.
>
>
>
> We need defensible measures of stove performance.  Can we please turn our
> attention to developing those, and leave the indefensible to history?
>
>
>
> Prof Philip Lloyd
>
> Energy Institute
>
> Cape Peninsula University of Technology
>
> PO Box 652, Cape Town 8000
>
> Tel:021 460 4216
>
> Fax:021 460 3828
>
> Cell: 083 441 5247
>
>
>
> *From:* Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On
> Behalf Of *Paul Anderson
> *Sent:* 15 February 2015 02:26
> *To:* Discussion of biomass cooking stoves
> *Subject:* Re: [Stoves] Examples of results of simmer efficiency Re:
> [Ethos] Additional presentations at ETHOS 2015
>
>
>
> Dear Dean,    my reply is below:
>
> 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 1:06 PM, Dean Still wrote:
>
>  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.
>
> I totally agree with this.   But it is not the whole story of LPSC.
> Other factors influence LPSC, especially concerning the measurement of the
> variables that are used to make the calculation.   These can include the
> insulation of the pot (incl. skirts), lid on pot, pot characteristics such
> as size, quantity of water in the pot at the start, and at the finish.
>
>
>
> Specific Consumption is based on how much energy was used to create
> simmered water.
>
> Simmered water is not created.   It was already hot at the start of the
> simmer phase of testing.   We are interested in how much energy is used to
> MAINTAIN the required temperature near boiling, but preferable about 3
> degrees C lower than that boiling temperature.   In fact, a
> super-insulative pot could need barely a flicker of a flame, and therefore
> even a well turned-down stove could cause the water to boil and
> evaporate.
>
> If the stove only operates at high power there is more steam made and [at
> the end of testing] less simmered water remains....
>
> that is true.   but continue.
>
> ..... so energy was used to create less product.
>
> Stove simmering is not creating a product.   It is maintaining a
> temperature.   The steam that is driven off does not represent loss of
> "product" which should be understood to be "cooked food" (and not meaning
> water that can be added to the pot by any attentive cook in a household.)
>
>
>
> I like Specific Consumption because it forces stove designers to make
> stoves that simmer successfully, not just boil water.
>
> I agree.   But the measurement procedures need to accurately document the
> ability to have that strong turn-down ratio, without calculations that can
> yield ambiguous or mis-leading results.
>
> 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.
>
> The cause-and-effect relationship is not totally clear.   We have wanted
> turn-down capabilities in TLUDs for many years.
>
>
>
> 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.
>
> I question the above wording to "evolve a perfect test" (which is a test
> run, not the test procedures.)   Maybe the statement should be that
> "knowing the characteristics let's folks operate their stoves in special
> ways to obtain superior results that are not realistic for average users."
> OR "... let's folks 'game the metrics' to present 'perfected' test-results
> BASED ON OPERATIONAL PROCEDURES AND NOT ON IMPROVEMENTS TO THE STOVES
> THEMSELVES."
>
> OR it could be that flawed protocols /procedures (such as dividing by the
> volume of remaining water after simmering) can yield numerical results that
> are questionable and perhaps disadvantageous to the development of clean
> cookstoves.
>
>
>
> Sam is doing great work as he crunches all the data....
>
> absolutely.   But we are questioning if the numbers are as valid and
> useful as claimed.
>
>  and gives ISO real numbers to work with in their discussions.
>
>
> Concluding statement:   The topic of Low Power Specific Consumption is too
> important to just brush aside the stated issues.   More "expert testimony"
> would be useful, including a mathematical analysis of the impact of the
> parts of the calculations.
>
> Paul
>
>
>
>
>
> 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
>
>
>
>
>
>
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