[Stoves] [ethos] Re: Laboratory Comparison of the Global-Warming Potential of Six Categories of Biomass Cooking Stoves

[Mr. Dean Still]

Dear Crispin,

As I pointed out to Tom, we just sponsored a very long series of tests
measuring the effect of moisture content on emissions and fuel use,
specifically responding to questions raised at ETHOS. It should be
available soon. Did anyone else investigate the effects?

The wood that we use for testing is left overs from a large carpentry
shop. It is the wood they use every day. It is not especially dried for
our tests.

It seems that you imagine that drier wood favors the rocket type
combustion. However, as you can see in the report the fan stove and Karve
gasifier did well using the same wood.

Perhaps you did not see that Rob Bailis addressed some of your points with
the WBT?

As you may remember, when we were testing the Vesto I repeatedly asked you
to come to the lab to run the tests. We try to carefully learn how to run
stoves before testing them. Having the inventor run the stove gives it the
best chance to succeed as Paul Anderson knows from testing frequently at
Aprovecho with all kinds of biomass.

I think the point is for all of us to remind funders what testing is
showing. People who are familiar with scientific investigation know that
the results of experiments only show what is investigated. Does this mean
that stovers should not do experiments for fear the results will be
misunderstood? NO, it means that more and more experiments should be done
to  fill in the whole picture.

All Best,

Dean

On Tue, October 9, 2007 8:45 pm, Crispin Pemberton-Pigott wrote:
> Dear Friends
>
>
> Given the stress caused by the disagreements around testing methods I
> agree that it would be good to push forward the agenda proposed early this
> year at the ETHOS conference.
>
> The main issues have not been debated in terms of what they are.  Here
> are five:
>
>
> Issue 1.	The fuel is not representative of field conditions.  It is
> extremely dry and does not burn like regular fuel.  There seems to be no
> reason given by Aprovecho for using fuel this dry.  No one presents
> justifications for it.  Yet over the strenuous objections of people
> including myself, tests that purport to 'compare' stoves are still being
> made and the results published, at least on the internet, sometimes in
> documentary form.
>
> Why does it matter?
> The fuel used in these tests cannot be used to establish performance
> benchmarks.
>
> Stoves that burn sticks on the end, like the Rocket  Stove, perform
> extremely well using very dry fuel. Other stoves including the Vesto,
> Juntos
> gasifiers, semi-gasifiers and any stove with a significant preheating of
> air do not do well because the fuel burns far too quickly, often running
> out of air, producing high levels of CO and particulates.  The Rocket
> Stove is
> optimised to burn that fuel; the stoves it is compared with are not.
>
> Issue 2.	The use of lids on pots for stove tests.  This has been
> discussed many times.  Stoves that are designed to operate at a certain
> power level are apparently tested with no lids on the pots, forcing the
> operator to run the stove above its design power output in order to boil
> the water in a reasonable time. This affects emissions.  During simmering,
> more fuel than normal is required to maintain the water temperature, even
> though the stove may be optimised to simmer at a very low power level.
> The Rocket
> Stove is optimised to operate a power level to boil pots without lids -
> years of research reports show this.  While some concession was made this
> year with regard to lids, it is not yet clear to me that the tests
> recently published were done according to the stove design parameters, or
> according to the UCB-WBT.
>
> Why does it matter?
> Unrepresentative tests give unrepresentative results.  Very important fund
>  decisions are made on the basis of test results, such as the level of
> CO2
> offset funding a stove type is going to receive.  If the test is
> unrealistic, the funder and manufacturer are being compromised.
>
> Issue 3.	Fuel heat rating.  There is a portion of the WBT that
> calculates the heat yielded during a test.  This means that taking into
> consideration the heat in dry fuel, the moisture content of that fuel and
>  the char remaining, an amount of heat offered to the pot is calculated.
> The
> UCB-WBT method is very accurate for only one species of wood and one
> charcoal type, but quite inaccurate for different wood species, different
> fuels, high moisture levels and different charcoal heat contents.
>
> Why does it matter?
> Tests done at different locations are difficult to compare with the ones
> done at Aprovecho unless the actual lab data is made available so the
> tests can be recalculated.  This data, in general, has not been made
> available by Aprovecho so the tests cannot be re-evaluated, nor can the
> claims made for comparative efficiency or fuel consumption be verified.
> The results from
> several months of testing different fuel moisture levels are not rendered
> acceptable because so much money and effort was put into them.  They
> become acceptable when the protocol is realistic and the calculations made
> as accurately as possible.
>
> Issue 4.	Thermal efficiency calculation method.  The formula used to
> calculate the efficiency of a stove involves comparing the heat offered to
>  the pot with the heat absorbed by the pot.  The one used in the UCB-WBT
> is not accurate.  There are errors introduced by the lack of lids: no
> account is taken of radiation from the hot upper water surface and the
> excessive evaporation with no lid.  The bigger error is the one that
> starts in the fuel heat rating and is then transferred to the efficiency
> calculation.  As the amount of charcoal remaining increases, as the heat
> content of the fuel decreases and as the moisture content of the fuel
> rises, the error gets larger and larger.  For gasifiers and users of low
> heat content fuels, the error can be well over 100%.  By this I mean that
> the calculated heat released can be double the actual value, giving the
> impression that the thermal efficiency of the stove is only 1/2 what it
> really is.  In other cases, the calculated value is very accurate.  Such
> calculation errors render meaningless comparisons made between stoves
> using wood of different species and moisture contents and, for example,
> rice hulls, as has been done with the latest set of published tests.
>
> The forthcoming test results for higher levels of fuel moisture mentioned
> by Dean are probably going to be presented within the UCB-WBT framework.
> If
> so, the thermal efficiency calculations and specific fuel consumption
> figures are invalid because of deficiencies in the methodology and
> formulae. The only immediate solution would be that the raw data for the
> tests be published so that the real performance can be calculated using
> various other methods, though that would still not solve the fuel moisture
> problem.
>
> Why does it matter?
> The UCB-WBT in its present form cannot be used to establish realistic
> performance benchmarks.
>
> Issue 5.	Variable and incompetent operation of stoves being tested.
> It is always a problem to get people who do not know how to use a stove
> really well to test it.  The problem will not easily go away.  The best
> answer I have seen is for developers to run their own stoves using fuel
> of their choice.  To do that at a central facility is very expensive.
> Testing
> a different places in the world and comparing notes requires an agreed
> protocol.
>
> I have suffered many times with products (other than stoves) being badly
> run by 'independent' testers so the problem is not unique to stoves.  In
> the case of the recent rice hull stove evaluation, the tester ran out of
> fuel part way through the test, yet reports the result which a reader must
> assume as being representative of the stove's performance.  This is not
> reasonable. Previous tests showed the CO emission to be 1/7 of this test.
> This is
> inconsistent and frankly, unbelievable.
>
> Why does it matter?
> It is dangerous because unfair accusations of bias can emerge if a stove
> is underperforming at Aprovecho when being tested alongside other expertly
> run stoves and the comparative results published as representative of the
> stoves performance in general.
>
> Improving the situation:
> A very large amount of goodwill have been shown to the people and
> institution of Aprovecho by many skilled and experienced people. No one
> will benefit from the publication of results that are correctly critiqued
> followed by more of the same.  A year ago these same five issues came up
> at a meeting in Bonn on the development of stove performance benchmarks. A
> year later the issues are largely unaddressed, with quite serious
> consequences for one of the stoves recently tested, the dissemination of
> which is dependant on funding determined by the CO2 and GHG mitigation
> value. Suppose these tests are believed?
>
> Failure to address these five fundamental scientific issues, now, at
> Aprovecho, can only lead to further complications and disaffection in the
> stove developers community.  If they are not addressed, there is a real
> danger that their results will be increasingly ignored.
>
> A lot of talented people are willing to contribute to this process.  We
> must enhance the store of goodwill that already exists between this
> eminent group of peers and deliver superior services to the world.
>
> Sincerely
> Crispin
>
>
>
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