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

Paul Anderson psanders at ilstu.edu
Mon Feb 16 04:01:58 CST 2015


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] *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  <mailto:psanders at ilstu.edu>    
> Skype: paultlud      Phone: +1-309-452-7072
> Website:www.drtlud.com  <http://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] *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
>     <mailto: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
>     <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  <mailto:psanders at ilstu.edu>    
>
>     Skype: paultlud      Phone:+1-309-452-7072  <tel:%2B1-309-452-7072>
>
>     Website:www.drtlud.com  <http://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
>     <mailto: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  <mailto:psanders at ilstu.edu>    
>
>     Skype: paultlud      Phone:+1-309-452-7072  <tel:%2B1-309-452-7072>
>
>     Website:www.drtlud.com  <http://www.drtlud.com>
>
>
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