Fwd: low power efficiency

[emma@george.as]

---- Forwarded message
From: emma@george.as
To: dstill@epud.net
CC: Visser@btg.ct.utwente.nl
Date: 28 Feb 2002 18:09:21 -0000
Subject: low power efficiency

Some of you gave me some advice on testing lorena and other woodstoves a couple 
of 
months ago. I have one more question.

I want to test some woodstoves also at low power, but it seems (to me) that 
efficiency at low (min. for boiling) power is a meaningless concept. In my mind 
I am not testing the stoves alone, but the Stove-pot-lid combo. In an ideal 
system no power would be required to keep a pot simmering, the power supplied 
by the wood is simply to compensate for losses in the system. An insulated box 
could do the same with no input.

If, on the other hand, I simmer without a lid (to measure inevitable evaporated 
water) a higher than realistic power will be required to maintain simmering. 

The only option remaining is to calculate energy loss (radiative, conductive 
etc) from the system which seems impossibly complex and pretty dodgy, and it's 
not really efficiency anyway - the energy can't be used in any situation.- 
Although I fully accept that steam produced in a high power test could 
correspond to useful power in a cooking situation.

I think I'm going to give up, and just find the savings compared to a 3-stone 
fire instead. Or I could give a combined high-low power efficiency, as in the 
VITA tests, eg. boil for 30 mins, simmer for 60. But since the low power phase 
represents only energy lost, not energy used, the longer the simmering 
(compared to high power boiling) the lower the efficiency. 

So the fair thing would be to simulate cooking, where no time should be spent 
high-power boiling, only heating and then simmering, with a lid. Then the 
useful energy corresponds only to that needed to bring the water to the boil??

It's very possible I've misunderstood something obvious. Could you advise?!

many thanks
Emma

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