[Stoves] WBT test results: metal grate with rock bed and conical pot skirt
Ronal Larson
rongretlarson at comcast.net
Sat Jan 25 20:31:04 CST 2020
List with ccs, adding the SNV report preparer in Viet Nam (Ha Hoang)
This is the additional set of comments I promised a little earlier today. To understand this, one has to carefully look at (and blow up) the photos - which are in here:
I insert my thoughts below in bold. I write here as I would in talking only to Kevin - but this seems like a good chance to get expert comments from our whole list. This is important data - because Kevin is developing something that is already saving a lot of wood. And no reason to think he has reached a limit. He is greatly fortunate to be getting this help from SNV (and I think at least some is being paid for only by Kevin!)
[SNV1: In the below tables and graphs below, the stoves performance parameters are presented in relation to the performance of Iron bar only and the LPG stove, the least and most advanced options in the stove stack of rural Vietnam.
[RWL1: I was impressed by this IB (= Iron bar) pot support. Should be in the $1-$2 range. Looks highly worth it (over heat draining large rocks or bricks).
One possible small addition would be some lower horizontal bars that might “mimic" the zero cost rocks under study. This assumes that the size of the rocks and the proposed horizontal “bars” have an optimum - and their small extra cost might have a quick payback. Rather than the IB’s rebar, which might have about a 1 cm diameter, these could be a factor of 10 lighter (and less costly)
I wonder if anyone has done a study of the best height of the IB. Looked OK - but probably can be optimized for different size pots and flames.
It was nice to see LPG in this table. Looks good/better - but we need to know the cost - which is likely many times more than the wood cost, especially if the wood is self-collected. Possible to get that LPG cost?
[SNV2: IB with a grate is superiour to the stone bed stove, but both signifantly save energy and emissions compared to iron bar.
[RWL2: This is a statement about cases A and B. Note that A’s “grate” is ceramic. So this says one might also prefer a ("costly”) grate over the free rocks.
I’d like to see the data on emissions - which are not yet sent to Kevin.
Why should the grate be better?
You have to study the photos to see possible reasons. The rocks are pretty large.
I can’t tell if this grate is supported from below by some small rocks (a later grate is). Could be that this grate operation could be improved (as the later metal grate of case C has given slightly better results)
Statements about C and D are below.
The first table gives two test outputs for 6 variations. The next table gives 4 outputs as differences for the right hand 4. I think we are missing a little by showing differences. I hope to see more data from these 6 runs - since I find this so valuable. Of course it would be nice to have multiple runs, but this is a great start.
Performance Metric
(Average from 3 tests)
Unit
Iron bar
(IB)
LPG
IB+Grate (A)
IB+Stones (B)
IB+rocks bed+metal grate (C)
IB+rocks bed+conical pot skirt (D)
High Power Thermal Eff.
%
23%
64%
35%
28%
36%
35%
Wood fuel equiv. consumed
g
877
227
466
606
472
508
on[RWL
Difference to IB only
IB+Grate
IB+Stones
IB+rocks bed+metal grate
IB+rocks bed+conical pot skirt
Total time taken (inclusive of lighting period)
26.0%
12.6%
29.0%
33.4%
Wood fuel equiv. consumed
-46.9%
-30.9%
-46.2%
-42.1%
Wood fuel equiv. cons./min
-57.9%
-38.2%
-58.4%
-56.7%
High Power Thermal Efficiency
49.3%
18.8%
52.0%
48.4%
[R
[RWL3: The first row above shows some surprisingly large differences in time taken. I hope that Ha Hoang can give some reasons - I don’t see a reason that time taken to start a boils should increase much. But if one is using a lot less wood to keep the temp just close to boiling, then taking longer with less wood is also a plus. - which might say the use with the skirt is best. I don’t understand this well yet.
RWL4: Case B is still a surprise for 3 bottom rows The other three cases are not much different from each other. But I think it could help hundreds of millions of stove users to do more work on further perturbations with rocks rather than grates.
[RWL5: I’d like to better understand the efficiency number - apparently doesn’t include the full test period? Only the high power portion?
I don’t see a good reason to stop and restart when reaching a boil. Would seem to make it difficult to compare tests.
SNV6. With all rocks bed setting variation (A, B, C, D), the efficiency and fuel consumption are substantially higher compare to iron bar only (IB). This is explained by superior air circulation with the grate/stones, more concentrated fire directed to the bottom of the pot that improves heat transfer and less heat loss to the ground.
[RWL6: Agree with most. But why is the fire more concentrated? Would this still hold if the IB itself was a little shorter?
SNV7. Fuel consumption and efficiency for Grate options (A and C) reduce more than rocks bed only option (B) since the grate allows for better air mixture and optimal combustion. The grate holes creates a better draft that is directed the fire.
[RWL7: Probably all true - and argues for grates over rocks. But maybe a better selection of rocks? I’d like to see a direct comparison between thick ceramic and thin metal grates. Finding an optimum grate could cost or save a lot of money.
Zooming in on the metal plate looks like maybe the holes were punched rather than drilled - which could be a major help in keeping them open. Three short bolts might give better performance than rocks below (and cost only a few pennies).
SNV8. The performance of ceramic grate is quite similar to the metal grate with 2 layers of rocks bed. However, as observed during the previous KPT, the ceramic grate is very easy to be broken so if disseminating the cooking innovation, the metal grate with rocks bed might be a more durable solution.
[RWL8: I vaguely recall the KPT. Probably little numerical data to help us to optimize. I hope others can chime in on comparing ceramic to metal grates.
SNV9 When putting the conical pot skirt around the pot (D) for rocks bed only option, the efficiency and fuel consumption was improved and closer to the Grate options (A and C). With this setting, part of the hot air instead of radiating outside, it will concentrated by the conical pot skirt and heating the pot. Therefore the heat was better optimized. Looking at the smoke went straight up around the pot in the video Conical pot skirt.mp4 could illustrate the above conclusion.
[RWL9: This could be the most exciting part of the report. The other 3 cases would seem to say the cone should also be combined - not with stones - but with a grate.
The mp4 link goes to https://drive.google.com/file/d/1JExCPpuKlBbzo50T5UfRG37l-mLybqxu/view <https://drive.google.com/file/d/1JExCPpuKlBbzo50T5UfRG37l-mLybqxu/view> . 29 seconds are worth watching.
Has anyone seen this particular type of skirt? The top of the cone is slightly larger than the pot. (How much?) I can’t tell how high the cone comes above the bottom of the cook pot.
It would be interesting to see more about how the flame flow separates away from the pot. Whether adding a more traditional vertical cylinder (not cone - or maybe the same cone??) could also be worth its likely relative small cost.
In sum, I congratulate SNV for doing a very nice job. And especially to Kevin for instigating (and paying?) for the test.
I look forward also to seeing how much char can be produced by a cook. Maybe with corn cobs?
Next for me is the justification for the present ISO WBT handling of this future char - my promised rationale for the “denominator equation”.
Ron
> On Jan 25, 2020, at 12:56 PM, Ronal Larson <rongretlarson at comcast.net> wrote:
>
> List: cc Crispin and Kevin
>
> I respond here because Crispin has attributed to me a WBT position I have never held. I also intend in two later messages:
>
> a. to talk about the test results that SNV has reported for Kevin re rocks and grates. (Which Crispin has misunderstood repeatedly below)
>
> b. to talk about the way that charcoal should be handled in any WBT (which Crispin has said (below and often) are wrong)
>
> See inserts below.
> :
>> On Jan 22, 2020, at 4:30 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com <mailto:crispinpigott at outlook.com>> wrote:
>>
>> Dear Friends
>>
>> This testing by the SNV lab has been done using their Simplified Water Boiling Test (SWBT). It is not the same as the ISO test in terms of calculations, and it is also not the same as the WBT in certain respects, being closer to the latter than the former.
>>
>> The important difference is that you will note in the report that was attached to Kevin’s message the use of the term “Wood fuel equivalent consumed”. This is the bugbear of that WBT – it does not report the wood consumed to operate the stove, it reports the dry wood fuel equivalent of the energy presumed to have been released from missing fuel mass, with a crude compensation made for the charcoal remaining in the ashes under the fire. The more char created, the bigger the deduction.
>
> [RWL1: Crispin is introducing charcoal for an unknown reason; SNV reports nothing on char. Probably a small amount of char was produced - and I guess it was probably handled correctly. In any case, any char amount was probably the same for all (5) tests
> The word “equivalent" was used in comparing to a test using gas - and I found that helpful.
> Repeat - I hope all will read the report. You won’t understand my remarks below without reading the SNV report - here:
> <SNV WBT Rock Bed with Variations.pdf>
> I have almost nothing on this fine report below. That is coming as item a) above.
>
>>
>> The problem with this approach (which dates back to 1985) is that the method was designed for stoves that all burn pretty much the same way, leaving about the same amount of char (as a % of total fuel burned). Kevin’s modification changes this % of fuel appearing as char at the end. Direct comparisons between stoves, in this case the same stove with a change, are not valid if one is purporting to report the fuel needed to light a fire and cook a meal. The WBT doesn’t do that.
> [RWL2: Crispin was apparently assuming a char aspect of the test that was not there.
> But this is still an important topic - coming later (my item b)
>
>> This issue came to light in 2007 when I made a big noise about it and some efforts were made to propose suitable corrections to the method. An ETHOS technical Committee as formed to correct the test, but did so under secret instruction not to have the resulting change invalidate a body of work that had already been completed. So that effort failed even though the problem was obvious, more so with stoves that produce a relatively large amount of char.
> [RWL3: I know only vaguely about this - but believe that a huge majority of individuals and countries approved the current ISO standard (that came out of the 2nd ISO panel - led by Jim Jetter.
>>
>> Ron Larson did his best to assert that the remaining char should be treated as unburned fuel that could be used in a different fire.
> [RWL4: I certainly wanted that energy in char be accounted for. It needs treatment very different from “unburned fuel”. We are talking here about what I have called the “denominator equation” - which remains in almost everyone’s WBT (thankfully).
>
>> He then planned to bury the char for carbon sequestration.
> [RWL5: I started worrying about this topic way before I had ever heard of carbon sequestration. My initial efforts in the early 1990’s were to save forests. I would support every/any effort to outlaw charcoal for cooking - unless that charcoal was produced in a stove (and almost none is - and in any case all char should go in the ground).
>
>> His position was that the stove should be made to look as if it didn’t use much fuel so it would get a high “energy efficiency rating” and then have the char to sequester and that such a rating was “needed”.
> [RWL6: Not a correct interpretation of my views. I applaud the use of “tiers” - they are helpful in getting cleaner and more efficient stoves. I think it critical that stoves that make char can be compared (via tiers) with those that don’t. I believe that Crispin thinks they should not be or cannot be compared. (Clarification requested.)
>>
>> A very long drawn out argument ensued in the halls of this channel and the ISO meetings about whether it was legitimate to report the “energy released value converted to an equivalent dry mas of fuel” or the actual fuel mass needed to run the fire.
> [RWL7: True - and the current ISO standard allows the comparison that I (and most stovers) desire.
>>
>> Now, for Kevin this matters a lot. The advantage of the rock bed and the metal grate on rocks with or without rocks on top is to burn the char instead of having it left over. It reduced emissions and reduces the fuel needed to cook. When SNV reports that there was a set of SWBT’s run and the difference between the three stove fire and the rock grate was a fuel saving of 35%, and the metric used was Wood fuel equivalent consumed, the answer given is actually high compared with a “real test” and low compared with a similar test conducted on a three stone fire. For example in one test the reported value was 38% but the actual value was 34% (a difference of more than 10% of value). The technical change saves more fuel than that, if the energy in the char mass remaining was deducted from the energy released from the fuel actually consumed for both stoves.
> [RWL8: I repeat - this SNV report never mentions the word “char”. Weird. The words “34”, “35”, and “38” refer to differences in geometry (5 variations), not charcoal.
> I probably talk to Kevin more than anyone reading this. His interest has so far not been in char - only zero cost methods of saving fuel (with obvious no-cost health benefits as well). The unique idea Kevin has brought to the stove “table” is using church groups for training. Reports to him are that millions have adopted the zero-cost efficiency methods - in a few months.
> Kevin is kindly hosting today at ETHOS a joint paper wondering if churches might similarly want to do the same for char-based stove systems that go beyond saving money - rather making money.
>
>> If anyone needs further clarification, I can provide it.
> [RWL9: Yes, please.
>>
>> If the test was a WTB or a char-deducted SWBT, the error is the same: the stove uses more fuel than the “Wood fuel equivalent consumed” indicates. However, the char remaining with the grate will be much less so the error (from true value) is smaller. This means there is a mismatch between the errors in the comparison report. The rocks+grate will have a smaller error than the three stove fire because the mass of char (as a %) is smaller.
> [RWL10: No comment possible - since (as far as I know) Crispin has totally mis-interpreted this test. If char was important, I am sure the SNV testers (who look like they have done an excellent job) would have reported char amounts and differences.
>>
>> If you have the spreadsheet that was used to create a test report, set the value of char remaining to zero for all three sections of the test and the mass of fuel needed to operate the stove throughout the test will be reported “reasonably correctly” if it was done near sea level.
> [RWL11: I totally disagree. As said above, a different rationale for the “denominator equation” is coming.
>>
>> When the adaptation or improvement to the stove results in a drop in the mass of char produced, a WBT in any form under-reports the level of improvement. The improvement is not “conservative”, it is “wrong”. In fact both are wrong, but one isnot as wrong.
> [RWL12: I doubt this is true - but to be continued. The converse says that as char production increases, the WBT over-reports. I don’t believe that.
>>
>> It is worth noting that the fixing of this error in the WBT has been strongly resisted by: Berkeley (LBNL), EPA, ANSI, Colorado State U, Illinois State U, PCIA, Berkeley Air, Aprovecho, GACC (currently the official custodian of the WBT) and Envirofit.
> [RWL13: Pretty impressive list!
>
>> The error (which in general over-reports performance, especially of Rocket-type stoves with no grate) is bundled into the calculations of hundreds of CDM, VCS, GS and VERRA carbon-trading projects.
> [RWL14: Can’t comment since I have no idea what the claimed error is.
>>
>> Envirofit and GERES both produced their own versions of the WBT but did not correct this fundamental error in reporting the fuel consumption. The former added two more errors, and GERES corrected one.
> [RWL15: Ditto.
>>
>> The new ISO standard lab test permits the reporting of a corrected version and the original erroneous version, and the wording is such that it is easy to be deceived into thinking one is the other. Worse, the Field Test mentions as a test method the Berkeley CCT 2.0 (2003) which has the same fuel consumption error, so that is a fail too.
> [RWL16: Ditto.
>>
>> In all cases, try to be clear about which test was used, which metric is being reported to you, and which errors have been included in the result. The difference can easily push your stove up or down one or in the case of char making stoves, two tiers. These test results are not interchangeable.
> [RWL17: I doubt.
>>
>> If you want to know what to use instead, try the EAP CSI Test used in Indonesia 2012-2017, later fully developed into the CSI test for stoves, heating stove and low pressure boilers. It is used as the default test method at the following labs:
> [RWL18: Cite? I have seen one paper from China that produced a lot of char and never measured it - not in their procedures.
> I look forward to Crispin supplying a more concise replacement of the equations in error and the corrected version. I am saying here that I trust Jim Jetter. I have not enough time to go looking for something that should only require a few right and wrong equations.
>>
>> SEET Lab, Ulaanbaatar
>> BEST Lab, China Agricultural University, Beijing
>> YDD Lab, Yogyakarta, Indonesia
>> Ministry of Energy Lab, Jakarta, Indonesia
>> SeTAR Centre, University of Johannesburg
>> Stove Testing Lab, Department of Geography and Environmental Sciences, North-West University, Mafikeng Campus, Potchefstroom, South Africa
> [RWL19: Yes - there was controversy from some of these groups and countries. I was never close to the voting, but think it was close to 10:1 against this view.
>>
>> Given that Kevin has achieved such significant results with very inexpensive methods, and that there is a real possibility the relative performance is being under-reported,
> [RWL20: Above, I read the term “over-reported”. Why now under?
>
>> it is perhaps wise to hold a session at ETHOS this year to discuss the implications and possible retroactive corrective measures that might be taken in light of the persistent refusal for years to correct these fundamental problems in performance assessment - but expect .
> [RWL21: I would hope so too - but expect confirmation - not correction.
>
> Ron (repeating my promised a) and b) from above)
>
>>
>> Regards
>> Crispin
>>
>>
>> From: Stoves <stoves-bounces at lists.bioenergylists.org <mailto:stoves-bounces at lists.bioenergylists.org>> On Behalf Of K McLean
>> Sent: Wednesday, January 22, 2020 11:22
>> To: Stoves and Biofuels Network <stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org>>
>> Subject: [Stoves] WBT test results: metal grate with rock bed and conical pot skirt
>>
>> SNV just released the attached test results that I find very exciting.
>>
>> Compared to an open-fire cookstove without modifications:
>> 46% less firewood - metal grate under rock bed
>> 42% less firewood - conical pot skirt.
>>
>> SNV performed Simplified Water Boil Tests (SWBT) which only tested thermal efficiency, not emissions.
>>
>> Metal Grate and Rock Bed
>> The first test was a modification of rock beds alone. Last year, SNV's SWBT showed a 31% improvement in fuel usage by adding a rock bed to an unmodified open-fire cookstove. In this new test, SNV added a metal grate under the rock bed and elevated the grate by a few very small rocks. With the metal grate and rock bed, fuel saving jumped to 46%, compared to the unmodified stove. This is a simple modification that can be made and sold for well under 1 USD.
>>
>> Conical Pot Skirt
>> A conical pot skirt directs the hot gases of an open-fire cookstove to the cookpot. It is easy to make and inexpensive to make, probably around 1 USD. SNV's SWBT found that it reduced fuel usage by 42%.
>>
>> The conical pot skirt has limitations. It may not work well with three-stone. (We are working on other pot skirt designs for three-stone.) In SNV's configuration, the skirt was custom made to the pot with a 1cm gap. Further testing is needed to determine the amount of efficiency lost when used with a smaller pot, and therefore a bigger gap.
>>
>> <image002.jpg>
> [RWL: Given above.
>>
>> We next need to test with rock bed, metal grate and pot skirt. I hope we'll find the fuel efficiency is improved by more than 60%.
>>
>>
>> Thank you,
>> Kevin
>>
>> Kevin McLean, President
>> Sun24
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