[Stoves] A call to stop using the WBT

[Crispin Pemberton-Pigott]

Dear Andrew

You write the most interesting messages.

Starting with this point:

>> Ron doesn't really want to preserve the WBT, he wants to rate stoves 
>> that have a fuel efficiency of 20% to be reported to be 40%.

>Not so he just wants the portion of fuel used to be accounted, in the same way the lpg used is calculated from what is left in the canister. You appear to want all the energy available in the initial fuel to be attributed to the cooking task.

You have that exactly backwards.  It is I who am insisting on the "LPG Tank Equivalent."

The mass of fuel drained from the pressure used to complete some task is the fuel consumed. The energy in that fuel is the energy consumed. I want the fuel mass consumed to be reported as "the fuel consumption and energy contained in that fuel to serve as the denominator when rating the cooking performance.

Ron, on the other hand, wants to scrape the soot off the stove and pot, calculate the energy contained in it, and report that the mass of fuel 'consumed' was less, because some of the fuel was turned into char, not burned. He holds that burning some of the fuel and leaving a sooty remnant is "an advantage" that should be used to increase the claimed cooking efficiency because he has found a use for this carbonaceous byproduct. Well, bully for him, but that doesn't reduce the mass of fuel consumed or the total energy in it.

The WBT agrees and deducts the energy in the sooty carbonaceous remnant, deducting it from the energy that might have been released from the fuel, and indeed, reports the cooking efficiency is higher than it actually is.

However useful sooty carbonaceous byproducts are, it is a crock to say that the fuel used was less than the fuel mass used. In your example, the mass of gas missing from the tank cannot be "reduced" by collecting unburned carbon.

>I can see where the fuel cost  is a significant part of income then it will be a factor in a cook's decision but it will be cost not energy that will be important.

Although Nikhil reminds us of the user and the decisions that underlie an interest in fuel economics, the fact is that CDM and GS projects use the efficiency metric to calculate fuel savings. If the mass of missing gas is 1 kg, then reporting it to be 1/2 a kg is misrepresentation and false.

To repeat:
>You appear to want all the energy available in the initial fuel to be attributed to the cooking task.

Of course I do. If one is reporting the cooking efficiency, then that is correct. If one wants to report the char energy produced during combustion, then it is the char energy divided by the input fuel energy.  If one want to report the combination of cooking energy and char energy, they should be added and divided by the same denominator. You get 'a number' but it is not the cooking efficiency. The WBT reduces the denominator, and then claims the cooking efficiency is higher. It is not higher, it is what it is.

The difference of opinion on this has to do with a hot topic in WG1 and WG4 at the moment: defining the system boundaries. I am surprised at the lack of clarity on where the system boundaries. Defining cooking performance involves the new fuel required to replicate a task for any in a series of identical replications save the first. (The first may provide partially burned fuel carried forward to the next test).

If you define the system as one for char production, then the metrics are similar, but they are not the same. If you define the system as cooking-and-char-making, again, different metrics are appropriate. One cannot claim to be rating cooking performance but include something lies outside the cooking system, and inside the char production system. 

If you want to rate the combination, do as suggested above - sum the two numerators. That is a third system and has a different boundary. 

> That fuel efficiency metric will be used to calculate the ‎reduction 
> in the harvesting of unsustainably harvested forests by improved 
> stoves accessing CDM funding. 

>This is a non sequitur, I don't know what fuel wood harvesting is likely to be unsustainable

Don't worry. It is taken care of. The CDM documentation has a great deal on the subject, defining harvesting, and what unsustainable means, and what fraction of a fuel resource is unsustainably harvested. Indonesia, for example, has been assessed as having no areas of unsustainably harvested biomass fuel. Chad does.

>I think this is the nub, this testing is about attracting funding and char making stoves feature in that, whether wood  harvesting is sustainable or not is a separate matter. It's a simple matter to calculate the costs in using a char making stove in that the wood input results in managing the cooking task and producing the char which may or may not have a value, this is separate from the  energy consideration.

Excellent. I am curious as to why you have been confused about the calculation of such a simple pair of systems. The wood input is the input mass. It is not reduced by the energy content of the char produced. Full stop.

>Char making stoves are sui generis, it's up to the cook to decide whether they prefer to use them for their low particulate pollution, the residual char for its value or both. I don't think this argument on testing protocols should be used  to persuade some quango or charity to foist one sort of stove or the other on users.

Excellent. The main channel for foisting has been the unsupportable claims made for stoves that are being promoted. A Rocket Stove from Aprovecho, for example, produces an above average mass of char, compared with, for example, a Rocketworks Stove from Durban. Because the remnant char from a Rocket Stove was used to inflate the claimed cooking efficiency, it looks as if it uses about as much fuel as a Rocketworks stove. But when rated correctly, the Rocketworks stove is quite a bit better because - big surprise - it consumes less fuel. 

Any reasonable protocol will report which uses less fuel, which is to say, has the higher cooking efficiency. The WBT doesn't because of its defective concepts.
 
>Whilst Xavier's argument  persuades me these protocols need addressing your dwelling on the  negative energy in the retained char makes me wonder that the existing test is in fact good enough.

I am dwelling on correcting bad math. Xavier has decided to advocate for elimination of the test and the disavowal of all test results made using it, and avoidance of it for any decisions involving money on account of its many fatal shortcomings. Long may he prosper.

Regards
Crispin