[Stoves] A debate about "efficiencies"..... was Re: ABCEG deceit and conceit

Thu Jan 12 23:27:36 CST 2017

Dear Paul

Let's tackle the big one first. What you wrote here is not correct, and the bone of contention is the difference between what you proposed and what Ron proposes, which is the same as what is in the WBT.

I have deleted the rest of the message. Here is your point 3.

"3.  On an ENERGY basis (not fuel basis), only the actual released energy in the biomass (after subtracting the energy that is still in the charcoal) should be used to calculate the heat transfer efficiency of the stove."

The heat transfer efficiency of a stove is an internal phenomenon. It is the percentage of the heat available in the gas passing the pot that makes it into the pot. To make the calculation one has to consider the energy released from the fuel, not the energy available from the fuel. That means CO, for example, and free hydrogen (H2) must be deducted from the heat available from missing (burned) fuel. It also means trying to discover the amount of energy remaining in all the fuel not burned. It is difficult to extinguish immediately on completion of the test. An error is involved.

Next, you have to analyse the remaining fuel - ALL of it - to determine the energy content. That requires a bomb calorimeter. Then subtract from the total energy, the gas phase losses and the remaining fuel energy to get the denominator‎ in the heat transfer equation. The numerator is the energy gained by the water in the pot (WBT) or the energy gained by the pot and water (India, CSI, BST etc).

That is not a cooking efficiency, it is the heat transfer efficiency and is useful to designers. It is not useful for rating the cooking performance of fuel consumption or relative fuel consumption. It is the misrepresentation of this number as 'the fuel efficiency' in the BUCT paper discussed here nearly last year which got me upset because it is against standard practice to make such a claim.

"So the formula (and Ron's second table) can be considered correct, "

No. Ron proposes something else. He proposes that SOME of the energy, an indeterminate fraction of the total remaining energy in the remaining fuel be deducted from the total energy in the fuel consumed, and that the gas losses be ignored. Of what use is the final number now? It is a useless number. It is not near the heat transfer efficiency, it certainly is not the fuel efficiency and it cannot be used to compare the relative fuel consumptions of two stoves.

What are the defects:
The total mass of fuel remaining is difficult to determine and will vary from one stove design to another.
‎The energy content of all remaining fuel is unknown and will not be determined.
The recovered fraction is subject to interpretation and opinion.
The fuel consumed, whether from the mass or energy content is not reflected in the final answer.
The metric, at least in the WBT, is a number of Joules, which are converted into an EQUIVALENT dry fuel mass, not the consumed dry fuel mass that was actually burned, but something else and it is called 'the fuel consumption'. If you don't believe that something that misleading would be reported as the fuel consumed, read the protocol and report sheet. We have been using the QUAD II report from CREEC lab for a few years as the worked example of this.

Ron is not looking for the heat transfer efficiency. He wants the low cooking efficiency number 'raised'. Tough. If you want a better fuel consumption number, use less fuel to accomplish the cooking task.

"...but it should be perhaps emphasized that the column heading should be:     EE-stove   (ENERGY Efficiency of stove)    and is not     FE-stove  (Fuel efficiency of stove). "

It is not the energy efficiency nor is it the fuel efficiency. It is just a number. The method does not determine either because it does not account for all the energy. You can't just 'leave out some of the energy' and claim to have calculated either figure.

The WBT final 'thermal efficient' result is being presented to stakeholders as 'the fuel efficiency' one way or another. People believe the number represents the fuel consumption, whatever it is called.  It is not. In the case of the QUAD II the fuel consumed per test exceeds the fuel needed to complete the test with an open fire. Yet the 'thermal efficiency' is reported to be twice that of the open fire, only because it makes so much char which the stove cannot use as fuel the next time it is used.

No amount of 'splainin' will convince a user that it uses less than half the fuel of an open fire, because it doesn't. Yet people may be paying for Gold Standard Offsets ‎on the basis that it does. It doesn't. That's cheating. Fraud, if you prefer that word because there was a warrantied performance presented to the funder and the performance was deliberately misrepresented as better than it is. False pretenses, right?

The 10,000 stoves being procured right now are only going to be purchased on the basis of a WBT 4.2.3 or equivalent result and there is a tier level to be assured, warrantied by an approved, experienced, lab. ‎All those test result misrepresent the metric the stakeholder is paying for.

Any engineer can look at the calculation and see that it doesn't represent the fuel consumption. Yet after ten solid years of complaints we still have engineers and scientists in the stove community bleating from the rafters that this is a legitimate metric calculated properly and has relevance to the performance comparison of all stoves.

For heavens sake, the three IWA low power metrics of the WBT don't even have a physical basis in science! Do have any idea how stupid that looks in professional circles? ‎No wonder people operating at the highest levels of development like Nikhil don't give a damn about claims for fuel efficiency. They have not been told something factual in twenty five years!

They want us to get our act together, yet in ten years the community can't admit to fundamental errors of math that any student can see in a few minutes of analysis!

Nikhil, what do you call it when a lab certifies that a stove uses half the fuel it actually consumes per cooking event?

Regards
Crispin
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