[Stoves] The need to continue the discussion Re: simmer efficiency
Dean Still
deankstill at gmail.com
Mon Feb 16 14:18:56 CST 2015
Dear Crispin,
Good point. The weight of water in the pot should start the same for
simmering. We can adjust mathematically.
I think we agree that, one way or another, a test needs a low power simmer
phase.
Good thing about being a part of ISO is that we get to look at things like
the WHO and improve.
Like you, I wish that WHO had better thinking in it.
Sam and I will write up a test for ISO to consider and perhaps you could
comment?
A consensus moving forward?
Best,
Dean
On Mon, Feb 16, 2015 at 11:33 AM, Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:
> 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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> http://stoves.bioenergylists.org/
>
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