[Stoves] Stove Definition - controllability

Fri May 3 00:04:25 CDT 2013

list cc Crispin 

Crispin asks a very important question in which char-making stoves probably will not look as good as all the others which control power levels by controlling fuel supply. 

The final Crispin question below is : 

"If I ask for a maximum power of X and ask for a demonstration that it can be controlled to X/4 is that reasonable as a minimum standard of proof?" 

My answer is no - not reasonable - as "minimum" implies that stoves not able to meet that criterion will be left out of all rankings or similar fate. Obviously X/4 is desirable, but why not X/5 or X/6? Some users will be happy with 2:1 if other features over-ride this one. My memory is bad on this, but I am pretty sure my early tests 18 or so years ago achieved better than 2:1. I could operate fine with maybe 2 square inches of primary air opening and with hardly any, with two coffee cans that probably had a max rating of a few kW. 

Few solar cookers get over a few hundred watts, but they can easily achieve 10 watts if you wanted that (and few would) by rotating away from the direct beam. 

We are talking of going through a fuel supply over an hour and also (different primary air opening) done in only 15 minutes. Anyone building air-controlled batch stoves have a current turn-down-ratio answer? 

I definitely think both the maximum and minimum power levels should be an output of the WBT (and are not now, I believe, except indirectly by reporting time to boil). But this should be accompanied by a statement of how quickly the changes can occur, anything unusual about accompanying emissions, and operator times required. 

I concur with Crispin that any stove not able to change power levels should be penalized at least by noting that fact.. 

Ron 

----- Original Message -----
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Sent: Thursday, May 2, 2013 8:12:43 PM 
Subject: Re: [Stoves] Stove Definition - controllability 

Dear Friends 

I would like to remind everyone that it is pretty important to a cook to be able to control the fire in some manner. There are lots of precedents so I won’t repeat them. I would like to have a minimum control exerted over the cooking power in order to qualify as a ‘cooking stove’. There are many appliances which are used for heating water, showers (like the Geyser 2000 etc) or drying fish and so one and on. But in order to ‘cook’ the fire has to be controllable. 

For an electric or gas stove this is fairly easy. In order to start things off, what does everyone think about a turn down ration of 4:1 where the turn down is ‘willful’ meaning it is controlled by the cook be either removing fuel, controlling airflow or by some other means. The reason is that stoves are appearing which definitely burn fuel and provide heat but are not very controllable (or not at all controllable). While one car argue that by brilliantly fuelling the stove in just the right manner a fire and its burn can be exactly matched to a cooking need – agreed this is possible – but is it ‘cooking’? 

When sitting in the field with cooks it becomes obvious that most cooking involves controlling the power at some point. How much control should be applicable to a stove in order to qualify as a ‘cooking stove’? 

If I ask for a water heating stove, it would not have to have any controllability at all – it just needs to heat the water within a certain time after which it can go out – no one will mind. But if we want to present a ‘solution’ (a cooking alternative to an open fire or sheltered fire) it will have to be manageable ‘to a certain extent’. 

Thus if someone says, “Here is my new cooking stove,” I can say, “Prove it can cook.” 

If I ask for a maximum power of X and ask for a demonstration that it can be controlled to X/4 is that reasonable as a minimum standard of proof? 

Thanks 
Crispin 

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