[Stoves] Aprovecho Stove Camp

[Frank Shields]

Dear Crispin,

 

Not sure I agree with all you say. 

 

We all know what simmer is. That is just by looking at it. It is not a temperature but a physical condition of the liquid in the pot. The temperature will change at that condition depending on what’s in the pot (salts, sugars beans etc). To do it scientifically we need a chart recorder  that records (plots) on plain graph paper the heat in the pot. At least five people are needed, each states when the pot is simmering and the third person to say ‘simmer’ we take that reading on the graph paper as the value we try to maintain over 30 minutes. After 30 minutes we (smart computer) draw a line through the center of the graphed line and determine the medium high and medium low to calculate the ‘offset of center value’ for the final number. 

 

The percentages of full power do –not- come into the picture.   It is the ability to maintain even heat at some temperature around ‘simmer’ for a particular stove that we should be concerned with. This change will make life much easier.   

 

Regards

 

Frank

 

frank at biocharlab.com

 

 

 

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin Pemberton-Pigott
Sent: Thursday, July 25, 2013 9:43 AM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Aprovecho Stove Camp

 

Dear Frank

 

You are really on the right track here. 

 

A ‘cooking stove’ has to be able to cook, period. That means controlling the heat somehow. The requirement to control the power level, and to vary it by a prescribed % - for example 50% or 25% of full power – is a reasonable requirement.

 

There is a proposed draft standard for biomass stoves that has a requirement to operate at full power for 20 minutes (to establish the fuel efficiency and power level) then to operate at 50% power for 30 minutes, maintain that power level within 20% of 50% for 20 of those 30 minutes. Next it should be operated at 25% of full power on the same terms. The purpose is to demonstrate that it is ‘controllable’.

 

A stove that can’t meet this level of control is not regarded as a ‘cooking stove’. It is perhaps a stove, but not one cooks will appreciate as being able to perform well.

 

All this is quite separate from the emissions and fuel consumption, meaning there are other targets that must be met as well (at the same time).

 

Electric stoves can be controlled over a power range of about 7:1 Gas stoves more. At 25% it is a 4:1 level of control. Not too demanding and not too little. This might be regulated differently in various countries depending on local preferences.

 

When conducting such a test, the thermal efficiency (meaning system efficiency so as to be able to report the fuel consumption, not the heat transfer efficiency) should be recorded so a performance curve can be generated. The curve should be printed on a card and attached to the product. If the performance is shown for the largest and smallest pots that suit the stove (in the manufacturer’s opinion), the range of performance that the customer can expect is indicated on the same card.

 

Regards

Crispin in sunny Beijing

 

 

Paal,

 

This is the way I am looking at it now:

1)      We first need to know if a stove can ‘simmer’. Forget the fuel savings for now.

2)      Stating an exact temperature for a lab ‘to simmer’ is not practical IMO because the water is heated at the bottom, thermometers differ, some pots covered etc. We just need to see if it can maintain a simmering temperature (say 85c to 98c?) and see how well we can maintain a steady temperature to determine if a stove can do that.  Low power. 

3)      Stove Camp, where my E-Mail was intended to address, is a place they like friendly competition for the best stove. Thinking this would be a good one for them. 

4)      Once we get a list of stoves that can simmer we can determine how well they do it based on fuel savings. First we need the list. And then we need to get the procedure established to measure stove efficiency that we agree upon. 

5)      Purpose is to determine if a stove will keep a constant Low Power  state over time. A most steady temperature reading will determine this. Nothing to do with fuel efficiency.

 

Cooking at low temperatures ‘Hay Boxes and the like’ cannot be included in this test because they would put the stoves being tested to shame.

 

Frank   

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