[Stoves] SPAM: Re: Advocacy action: ask the GACC to stop promoting the WBT

Tue Feb 14 23:27:05 CST 2017

Dear Frank

The problems with the WBT are more fundamental than you describe.

It must be faced, square on, that the WBT calculation does not provide the efficiency. The formula is wrong!

If you create a stove as you suggest, and measure the efficiency using the WBT, and it says the cooking efficiency is 40%, you would be happy. Then if you used a different test like the Chinese one, it might say the efficiency is 25%. So, which is it?

I am telling you that there is a problem with the calculation, not the concept of testing.

Here is something practical you can do to prove it: Get a set of numbers from a stove test, the fuel consumed, the char balance and so on, water masses and temps. You can invent one or use a real stove. Then enter the same set of numbers into the various versions of the WBT:

VITA 1985
WBT 2.0
WBT 3.0
WBT 3.1
WBT 4.0
WBT 4.1
WBT 4.1.2 of October 2011
WBT 4.1.2 of April 2012
WBT 4.1.2 of June 2012
And finally
WBT 4.2.3 of 2015.

You will get 10 different answers.

And not one of them will be correct because there are systematic errors in the concepts underlying the calculations plus errors in the formulas themselves.

‘Perfecting’ a stove using incorrectly calculated metrics is not going to lead to stove nirvana. The Indian, SeTAR and Chinese tests all perform the calculation more or less correctly. The Indian test uses an inappropriate fuel in that the stove has to be optimised to that (100% dry) fuel in order to perform well. No one in India uses such fuel so the stove is optimised to an inappropriate air pre-heating and air-fuel ratio. They have been advised to revise the test.

The Chinese test uses a very different approach conceptually as it includes a burn-out phase which raises the reported efficiency by about 11% of value. That is something applied to all stoves and fuels so the result is ‘fair’. There is a small miscalculation in the efficiency from double-counting. (For fun, I challenge the readers of this list to find it. It escaped detection for decades.)  It can easily be corrected. They have been advised to revise that calculation.

The WBT contains several important errors. When the IWA text was proposed, I reviewed it and reported some of these errors to the committee. For the most part they did not correct the errors, marking them as ‘too small to worry about’ and ‘to be handled later’ and ‘for later discussion’, that sort of thing. Thus there was public input on the IWA text but the corrective information was not applied to the result.

In the IWA meeting numerous discussions were held on metrics, names of metrics, ideas about what could be in the document. A lot of the meeting time was taken up with presentations on how the document was prepared. The tiers were presented and as the numbers were dependent on WBT results, many of us knew they were unimportant as they would have to change when the test was corrected. The IWA event was conducted in the following manner: “We have already agreed in Lima on what should be in an international test method so all we have to do is rubber-stamp it and we can go home.”

That was of course not acceptable as the Lime event just gave the WBT 4.1.2 the nod without examining it closely nor correcting the manifold errors. To get our (South Africa – 6 delegates) agreement, it was critical to have any test method approved by external, expert reviewers, which obviously had not been done before. This text was added and we all voted for it. It would be quite incorrect for anyone to suggest that we approved of the whole content because, for example, the IWA has 9 performance metrics and the WBT only produced on of them, efficiency, and calculated that incorrectly. Yet it was the ‘default method’. With only one metric being produced, and there of the nine being physically invalid, there was little hope the IWA and its testing and tiers could deliver on the promise of ‘better stoves’.

Consider what happened since: the requirement to have all test method examined externally by experts was never implemented for the WBT. It would of course fail because of the invalid metrics and the bad calculations.

When new got to the ISO we were told, “The IWA in ins place and everyone is using it so all we really have to do is rubber-stamp it and we can all go home.” That of course didn’t happen. Votes were held kicking out all WBT-forms of test and also the tiers. Let me repeat: the vote by the experts was that there should be no WBT and no tiers in the Standard.

If you find tiers in the ISO standard it is not because the experts wanted them or voted them to be there. For the IWA it didn’t really matter because the requirement to have the test methods reviewed would have killed any tiers they were based on – assuming that the IWA was actually implemented, which of course it was not. People pick the bits they like.

>The WBT used exact sized, dry and consistent wood type for the testing to establish the best gaps, insulation, height and etc. measuring performance of energy entering a pot of water.

Aprovecho has claimed many time to have done exactly that. I challenge this claim. They optimised their stoves to get ‘good numbers’ on the WBT which does not report the actual performance. Sometimes it is similar to the real values, sometimes is it not. It largely depends on how much char is produced. The more the char, the greater the over-claim.

The AWBT from GERES is better on that particular metric, even though it is not perfect. Bottom line: Do not develop a stove using the WBT. It will mislead you.

Regards
Crispin

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20170215/0c54df8f/attachment.html>