[Stoves] Fuel Testing

[Crispin Pemberton-Pigott]

Dear Andrew

I was going to say that surely we could model that....

But it would be more useful to model the heat loss in the steam at the pot 
sides.

I have allowed for conservative calculations when making claims for 
efficiency because it is useless to overclaim.

So, I have been deducting a bit of the 'fuel used' to compensate for 
moisture on the basis of heating it from ambient and boiling it away.

I have not added in an additional amount for the lost hot steam because that 
does get lost in real life.

Maybe what should happen is that the loss from moisture in the fuel shold be 
calculated to a certain standard, for example to 12% (air dried) and if you 
are using 5% moisture wood, you should subtract from the efficiency to give 
enough energy to the heating of water that _will_ be there in the field.

Actually there is merit in this.  Even it if was 10% (dry season air-dried), 
it is a nice round number.

If your wood is 16% moisture WWB you deduct at a certain rate (Andrew 
proposes 2.7 MJ and if it is zero, you add.

This is reasonable and when testing in the field, it will represent reality 
better, and measurements made from real life tests where the moisture 
content is unknown will be more useable for international comparison.

Al things said and done, working with a round number is no easier than a 
square number: how about we ask people what they get as the actual moisture 
content of fuel and settle on something realistic as the heat content for 
stove evaluation purposes?

I think it is important to get away from lost-water-based testing (which is 
for developers) and move to fuel-used testing with agreement on a heat value 
for the wood, on the mass that forms the basis of the specific fuel 
consumption calculation, and the basic procedure.

Regards
Crispin


----- Original Message ----- 
From: "AJH" <list at sylva.icuklive.co.uk>
Subject: Re: [Stoves] Fuel Testing


On Tue, 03 Oct 2006 13:07:04 -0700, frank wrote:

>I would think a wet piece of wood would conduct heat through the wood
>faster. Water transfers the heat.

The point being that water only transmits heat up to a temperature of
about 100C, then it turns to steam absorbing much higher amounts of
heat than the heat necessary to reach that 100C. So there will be a
plateau temperature held at 100C whilst the water evaporates before it
can start rising up to pyrolysis temperatures.

AJH