[Stoves] A call to stop using the WBT

Tue Jan 30 00:20:56 CST 2018

Part of the problem with the WBT is its abuse of efficiency. It is
fundamentally flawed to subtract the energy contained in any char from the
energy in the fuel fed, in calculating the efficiency. 

The first thing you want from a cookstove is that it should cook.  So you
define its efficiency as the energy actually delivered to the food divided
by the energy in the fuel actually fed to do the cooking. That is the
cooking efficiency.

If you produce a char by-product which is useful, you can similarly define a
char production efficiency as the energy in the useful char produced divided
by the energy in the fuel originally fed. It tells the char user what he
needs to know, namely whether the cookstove does a good job of turning some
of the fuel into char.

If you insist of subtracting the char from the fuel fed to calculate an
efficiency, as in the WBT, you get a meaningless number.  It does not tell
you how efficiently the cookstove cooks, and it also does not tell the char
user whether the cookstove does a good job of turning some of the fuel into
char. 

Philip

-----Original Message-----
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Andrew Heggie
Sent: Monday, January 29, 2018 10:40 PM
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] A call to stop using the WBT

On 28 January 2018 at 12:26, Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:

>
>>> 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.

You again wilfully  misrepresent my statement: your method is analogous to
weighing the tank and its contents, subtracting the empty weight of the tank
and attributing all of the energy in the lpg to the cooking task in hand
despite there still being energy left in the lpg remaining in the tank.

In a similar vein: were I to cook by biogas you would have me calculate the
mass of all the vegetation that went into the digester and say that was the
mass of fuel used whereas only the few cubic metres of gas produced was
actually used in the cooking task.
>
> Ron, on the other hand, wants to scrape the soot off the stove and 
> pot, calculate the energy contained in it,

Again this is a gross misinterpretation, we are saying the TLUD is a gas
generator and the flame is doing the cooking, only the char remaining in the
stove at the end of cooking  that has an alternative use is to be allowed
for, soot on a pot is clearly a waste product of the combustion.

<snipped drivel>

>
> 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.

As soon as you mention sooty it is a waste product of incomplete combustion
and distinct from char.

> 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

My point proven then

> 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).

Pass on this one but we are not even in agreement here as  the TLUD char is
not partially burnt fuel, it has become an intended part of the production
of a pyrolysis offgas which in turn is the fuel used in the stove.
>
> 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.

Why not? The char production part produces the gas for the flame that does
the cooking, we can say, within the bounds of measurement, that the char
contains a percentage of the  initial energy and the gas has the rest. The
gas flame then has an efficiency  in which it heats the pot.

>
>>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.

I'm not confused, the wood input is to the TLUD, the energy to the cooking
pot is from the burning of the offgas and just because you talk loudest
doen't give you any right to put a full stop on people that disagree with
you.

>
>>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.

Again a non sequitur of which I know nothing, I don't promote any stove, you
on the other hand do.

>
> 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.

> I am dwelling on correcting bad math.

No you are intent on disadvantaging char making stoves. You are manipulating
your preferred spreadsheet in order to do so.

Andrew

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