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

[frank]

Crispin and Stovers,

I agree with the procedure Aprovecho is using for testing stove design, 
heat transfer, air requirements etc. When doing any research everything 
needs to be the same (including fuel) - except for the one  variable 
that is being tested. The data of lids on pots, space around pots, 
location of pots in regard to the flame how having a pot on the stove 
effects emissions etc. all need be tested using the same fuel. Dried 
sticks all the same size and placed the same is the way as done at 
Aprovecho is also how I would do it. Aprovecho is testing stove design 
and heat transfer and the data produced is important for making the 
perfect stove. This work needs to be continued as-is. I suspect the 
findings can be used for most any heat source.

In another section of the Aprovecho Lab and elsewhere there could be 
other research going on that test the different heat sources (fuels) and 
the requirement to get even pyrolysis, emissions suitable for clean 
combustion, continued combustion, with the maximum amount of heat 
produced from the fuel.  This being very separate from the stove heat 
transfer experiments. 

Then the findings from the heat source is connected with the findings 
from the heat transfer experiments to make the perfect stove for the 
fuel chosen.

So testing the heat source is just the other half of what needs be done IMO.

Regards

Frank



. 




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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>
>
>  
>

-- 
Frank Shields
Soil Control Lab
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Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com