[Stoves] A call to stop using the WBT

[Andrew Heggie]

On 30 January 2018 at 06:20, Philip Lloyd <plloyd at mweb.co.za> wrote:
> 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.


Doh that just takes us back to the beginning, there may well be other
problems with the WBT  but this treatment of the energy in the char
remaining from a TLUD burn is not one of them.

Even Crispin has acknowledged that one of the protocols allows for
char from one burn to be carried over to another test, this therefore
acknowledges the energy remaining  after the cooking task is finished
has some value, allowing for the energy in char from a TLUD burn is
just an extension of the same idea.
>
> The first thing you want from a cookstove is that it should cook.

Absolutely no question about that


> 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.

Well we can agree about most of that but it's the burning offgas that
is "fed" to the cooking in the case of the TLUD stove and not the char
that is retained.
>
> 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.

Okay but while that char has  energy which the user is aware of they
are similarly aware that the same energy cannot have been "fed" to the
cooking pot.
>
> 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 is not meaningless, it tells the user  what proportion of the
energy was "fed" to the stove and what energy is retained in the char.

>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.


Of course it does but I acknowledge there may be some difficulty in measurement.

Andrew