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

[Dean Still]

Dear Crispin,

You take a standard pot of water.

You boil the water and see how much fuel was used and how many emissions
were made.

You simmer water for 45 minutes.

You then try to make a stove that uses less wood and makes fewer emissions
to do the same task.

Eventually you evolve a much better stove.

When I started experimenting with stoves they used around 550 grams of wood
to boil 5 liters of water.

Now stoves routinely use around 300 grams.

Stoves used to make lots of PM and CO.

Now stoves make much less because stoves evolved using testing with
emissions equipment.

There are now biomass stoves that meet the WHO indoor air quality
guidelines. This seemed almost impossible a few years ago.

For example, some TLUDs are now really great stoves. They are clean burning
at high and low power. The newer Tom Reed type fan stove doesn't put soot
on pots! The Rocket stove is better. There's lots of better stoves now
including side feed fan stoves. Folks cooked on them at ETHOS, etc.

I am a simple guy. Testing with emission equipment has been the tool that
has created this progress. The cooks add critical functionality and having
cooks help to design the stove is necessary to create a stove that is
acceptable to them.

I admire your energy and I hope it helps us to make more progress through
stove testing. Folks need better stoves to protect health, etc.


Best,

Dean



On Thu, Feb 19, 2015 at 10:52 PM, Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:

> Dear Dean
>
>
>
> I too will try again:
>
>
>
> The WBT is not a good lab tool because it mis-reports the performance and
> convinces people they have a ‘superior’ stove when it may not be. That is a
> problem that will not go away. What we are discussing is why the approach
> doesn’t work.
>
>
>
> >The WBT was designed to be a lab tool.
>
>
>
> I disagree. It was originally designed as a tool to use where there was no
> lab by people who did not fully appreciate what they were doing.  If they
> had, the original test would not have included questionable assumptions,
> some poorly selected and invalid metrics.
>
>
>
> Sam Baldwin introduced the metric ASFC – the average specific fuel
> consumption contaminating what could have been a valid metric for high
> power with the invalid low power version. It is reported in the snip I sent
> from Rani et al in the right column. It is the simple average of the ‘PHU’
> numbers for high and simmering power so it is wrong on two counts.
>
>
>
> Without a valid set of metrics like ‘Fuel Consumption’ and “combustion
> efficiency’ testing does not inform the designer what he or she needs to
> know. The heat transfer efficiency would be OK if it was calculated
> correctly, but it is not – not the way an engineer understands the term as
> applied to a boiler. The proper calculation ignoring chemical and
> mechanical losses, gives the system efficiency, but only for a continuous
> operation with continuous fuel. Considering the losses gives the heat
> transfer efficiency.  The WBT cannot apply in a valid manner to a biomass
> cooking stove because they are started and stopped and generate waste fuel
> and charcoal. The errors are conceptual and have not yet been corrected.
>
>
>
> >The CCT and KPT are used to make stoves that please cooks, meet
> requirements in use.
>
>
>
> This is not making any sense. The claim has been repeated for years and it
> has never been correct. A lab test that cannot report correctly that the
> performance has actually been improved is of no value. A set of tiers based
> on such performance ratings has no value either.  It is indefensible. And
> that is before looking at the usefulness of tiers, which is for another
> discussion.
>
>
>
> The CCT also has invalid metrics and makes other mistakes in calculations
> and concept so has virtually no value for regulatory or policy purposes. It
> would never pass a critical review.
>
>
>
> The WBT ‘fuel efficiency’ number (which is energy supposedly released
> turned into an equivalent fuel mass) may have little to do with the actual
> fuel consumption except for certain stoves using certain pots employing a
> certain burn cycle. That is bad, because it means it treats different
> stoves differently.  That partly explains why the WBT and CCT numbers don’t
> match. First, they measure different things in a different manner using
> different definitions, and second, neither reports the actual performance.
>
>
>
> The KPT is not a stove test. It is a test of household behaviour related
> to their use of fuel. KPT results also do not match the CCT or WBT numbers.
> Again, it measures different things and cannot spot changes of consumption
> that have nothing to do with the stove, but which *do* have to do with
> fuel use. Many people who suddenly have more fuel available cook and heat
> differently, or just watch the fire, or study books longer. Measuring the
> fuel going into a home is not testing the stove, it is testing the family.
> It is interesting and can be used for evaluating the results of a stove
> program, but not a stove per se.
>
>
>
> >The instructions in the WBT, CCT, KPT plainly state the intentions.
>
>
>
> The documentation has claims that are not borne out in theory or practice.
> ‘Intention’ is not ‘achievement’. The authors clearly didn’t understand the
> design of experiments. That’s OK I guess, but we can’t be advised to use it
> for real work and the spending of real money. We would be charged with
> professional malpractice, the same as in any other field, for knowingly
> using a defective method. If it is use unknowingly, it would speak to a
> lack of competence.
>
>
>
> If a doctor prescribes a defective test that can’t detect cancer, and the
> patient dies because of undetected cancer, the family has a right to raise
> questions. If a stove is claimed to address indoor air pollution by
> reducing PM2.5 by 90% and it doesn’t, the one making the false claim is
> liable for consequences.
>
>
>
> Investigating the root causes of the multiple failures of the WBT shows
> why it doesn’t report or predict performance, in the lab or anywhere. The
> WBT has numbers calculated based on variables and metrics with conceptual
> errors and reports performance using multiple metrics that have no place in
> an engineering report.
>
>
>
> The new WBT spreadsheet, much modified for the LEMS/PEMS hood, has at
> least 118 systematic errors affecting the results. I don’t have time to
> find them all.
>
>
>
> The CCT is a test of a single meal which cannot be representative of
> average use. It similarly suffers from numerous (but not as many)
> analytical errors. Error propagation contaminates other results.
>
>
>
> The KTP is a test of fuel consumption by a family. When people get a much
> improved stove they change their pattern of energy use and the KPT does not
> detect that, attributing all changes (or none) to the stove. There is no
> way to save the KPT as a ‘stove test’ unless it is rewritten from scratch
> as a test of the stove. It is a good test of a program of intervention.
> Christa Roth reported that 70% of the minor fuels savings gained by the
> introduction of the Mandeleo stove in Malawi were the result of ‘household
> training’ which could have been done across the country without changing a
> single stove – to much greater total effect that the stove making program.
>
>
>
> The only valid measurement of field performance is an uncontrolled cooking
> test (UCT). Omar Masera, Marcelo Gorritty and I came to the same conclusion
> independently and can argue why this is true. I made it on this list maybe
> 7 years ago. Omara made it again at the Phnom Penh conference. I supported
> him at the time. He is correct. I think his method can be improved.
>
>
>
> >Aprovecho uses the CCT when we want to design a stove with the local
> cooks using their foods, pots. They operate the stoves. The cooks should
> design the stove.
>
>
>
> Cooks cannot design improved high performance stoves. For one thing,
> nearly to a man-jack, they do not know what to measure or how to express
> those measurements.  Knowing math, physics and thermo-engineering is a good
> start, but knowledge does not make someone a stove designer. They may have
> no skill at integrating user information and design something in abstract
> in their garage that no one wants to use.  Users contribute information in
> the same manner that any industrial design team is provided with ergonomic
> and performance requirements and cultural preferences.
>
>
>
> What do the following award winning stoves have in common: Kimberly,
> Vesto, Prakti charcoal, Biolite, Oorja, World Stove, Free State Paraffin
> Stove?
>
>
>
> They were all designed by teams that included an industrial designer, some
> an anthropologist.
>
>
>
> The CCT is sort of on the right track if people are allowed to perform the
> range of cooking they require.  But that turns it into a UCT and would
> still requite the metrics and calculations of the CCT to be corrected.
>
>
>
> >The WBT teaches how to improve stove technology. Two very different uses.
>
>
>
> The WBT does not teach me how to improve a stove technology because it
> reports several wrong things incorrectly calculated, some even in the form
> of invalid metrics. It does not report fuel consumption, the heat transfer
> efficiency nor the thermal performance, nor the specific fuel consumption.
> It just *claims* it does. Further, it demands that the burn cycle be
> fixed which is conceptually in error. Just as an atypical drive cycle for a
> car cannot tell me what the fuel consumption is for my cycle, an atypical
> lab burn cycle can’t tell me what the performance is for my cooking.  I
> have to use my cooking cycle.
>
>
>
> In a more recent message is the claim:
>
>
>
> > The WBT is usually used for comparisons of performance because the
> results are internationally comparable.
>
>
>
> This is *also* incorrect, both conceptually and factually. What does
> ‘internationally comparable’ mean? Does it mean that another lab using the
> same stove and fuel and the same burn cycle will get the same result? In
> theory this might be possible *it they do not use the WBT* because the
> WBT contains assumptions and metrics which invalidate the answers. Because
> it selects incorrect variables to use in dubious calculations, the answers
> will never agree even if the labs are good. The proof is to do the same
> test in the same lab with the same stove and the same fuel and conduct the
> same burn cycle under the same pot. Even then, you don’t get the same
> answer because the WBT has a 30% inherent variability in its results. On
> top of that are the experimental errors.
>
>
>
> BTW that number 30% is calculated on the basis or a large number of tests
> used as seed data in a Monte Carlo analysis of 100,000 computer generated
> WBT’s. It is a test of the test. It confirms observations in labs and the
> field: that WBT results are not repeatable. They are not repeatable for
> known reasons.
>
>
>
> Further, the use of such a round robin test is not done to find the
> performance of a stove, rather it finds the performance of a lab. The ISO
> uses such a test to rate labs.
>
>
>
> The round robin idea is incorrectly applied to the testing of stoves. In
> short the notion is conceptually incorrect.   Why is it incorrect? Because
> the answer, the performance using a particular fuel and burn cycle, has no
> value to potential users. An ‘international rating’ of performance made
> using atypical burn cycles, pots and fuels imparts no useful information.
>
>
>
> A biomass stove burning solid fuel cannot be rated out of context the way
> an electric stove can.  Well, I have to qualify that: electric motor
> ratings are based on the ‘type of electricity’ because there are two types.
>
>
>
> Look at the name plate on an electric motor. It has two ratings for two
> different types of ‘fuel’: 50 cycle and 60 cycle per second electricity.
> The maximum performance, the horsepower, is rated differently for different
> ‘fuels’. There is no ‘universal’ metric for electric motors. With that in
> mind, one can see that an acceptable universal test for a biomass stove is
> impossible.
>
>
>
> The cold start, hot start, simmer is almost no one’s burn cycle. The burn
> cycle dominates emissions and efficiency ratings. That is yet another
> reason why the WBT can’t predict performance in use.
>
>
>
> Dean, you have made two important, contradictory claims:
>
>
>
> 1.      The WBT is a designer’s tool which means it is not for evaluating
> actual performance.
>
> 2.      The WBT is useful for making comparisons internationally which
> implies it can be used for evaluating actual performance and sharing that
> rating internationally.
>
>
>
> The Berkeley-sourced stove comparison chart is obviously based on the WBT
> and makes claims to display stove performance relative to each other and in
> absolute terms on a set of 5 performance tiers. The GACC is using that
> document/record and encourages everyone to report their test results in
> that format. There is even an automated tool for doing so over the
> internet.  Thus the WBT *is* being used for rating actual performance
> even while its principal authors admit is should not be.
>
>
>
> Uncorrected, the WBT is not a useful tool for designers. International
> comparisons have little to no practical value because people use hundreds
> of different biomass fuels and thousands of cooking cycles in myriad
> combinations, each of which changes the performance results.
>
>
>
> The only possible solution is to use a valid testing framework reporting
> valid metrics and apply a locally relevant selection of fuels, pots,
> cooking cycles and operating techniques. The result is valid for the
> combination of fuels, pots, stove and operating cycle, and no other. That
> is Just How It Is.
>
>
>
> This is already well-accepted in the vehicle and health fields. In fact it
> is hard to find an industry that does not apply this rather obvious reality
> – from roof shingles to tires. Imagine if all tires were subjected to the
> same loading and speed conditions and given an ‘international rating’. It
> is a dream to soar with the eagles, but that pig has no wings.
>
>
>
> Regards to all
>
> Crispin
>
>
>
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