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

Mon Feb 16 01:15:31 CST 2015

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 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   
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] 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 <tel:%2B1-309-452-7072> 
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 <tel:%2B1-309-452-7072> 
Website:  www.drtlud.com

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