[Stoves] Fwd: Simmering test

Sun Feb 15 22:50:30 CST 2015

Dear Raman

Many thanks for popping in with those references.

We do not have to drop simmering from a cooking task – you can have it if you want. Hopefully you are testing according to local conditions where the stove will be used so the rating you are giving the stove has some relevance to the performance in use. If it is rated doing something people do not do, the result has no value or even negative value if people believe it represents what they are getting when the buy the stove.

My point is that while you can choose any cooking cycle you want, you cannot report the performance using invalid metrics. As explained in the message to Paul, there is no such thing as the efficiency of not accomplishing work. 

What is the ‘thermal efficiency’ of a retained heat cooker which uses no fuel at all? A billion %?? The metric is not appropriate for the desired rating. You could report the energy used, but then you have to consider whether the retained heat from the boiling phase was also making a contribution. That means considering the simmering separately from the rest of what happened renders any result invalid because there is no practical way to determine the heat coming from a cooling stove body, and that quantum of heat will vary according to what happened before – it is not an inherent property of the stove so there is no point comparing stoves on that basis. 

I have seen a stove that accomplished a 45 minute simmer with retain heat only from the stove body – no fire at all. What is that ‘thermal efficiency? A billion%? The concept is silly.

Picking the wrong metric and then rating a stove performance using it is anathema to an engineer or a physicist. Making up justifications doesn’t enhance the prospects for using an invalid metric.

The consequences of using the wrong metric are clear. If a stove puts 2 MJ into a pot while simmering and another identical stove puts in 1 MJ because it was turned down more, and both stoves generate 1000 mg of PM2.5, the stove that was turned up slightly reports “500 mg PM2.5/useful MJ”. The one that accomplished the turndown to simmer with less water loss gets a rating of “1000 mg/useful MJ”. That is indefensible. They both emitted the same mass of PM and the one that turned down better gets rated with double the ‘emission rate’ according to the IWA. 

No product regulator is going to accept such a thing as a guide to importation and performance targets in their country. 

Performance testing needs a ground-up review to establish valid metrics that inform the users about what they can expect.  Just because people have been using invalid measurements or metrics for years does not matter one whit. 

Regards

Crispin

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Raman P
Sent: Monday, February 16, 2015 10:31
To: Discussion of biomass cooking stoves
Subject: [Stoves] Fwd: Simmering test

---------- Forwarded message ----------
From: Raman P <raman03 at gmail.com <mailto:raman03 at gmail.com> >
Date: Sun, Feb 15, 2015 at 11:50 AM
Subject: Simmering test
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org> >

Dear all,

It it is interesting to see a lot of discussion on simmering test. This is one of areas of WBT, needs more clarity.

As per the discussions, at many time simmering test can give a misleading result about the efficiency of the cookstove.  During the summering phase the vessel gets the thermal energy from two sources one is from the fuel and another one is from the stored heat, which is released from the cookstove material. Hence when we quote the efficiency of the cookstove, it should be the fraction of the total energy input (sensible heat + latent heat) transferred to the vessel over the total energy input , during the complete WBT. Simmering phase test cannot be dropped from WBT, even though it is not the only parameter used to evaluate the performance of the cookstove. But, simmering phase is an important part of cooking practice. During the actual cooking, the stove is not operated only at high power. For example, boiling milk is a tricky process and control over firepower is very important. When a cook can boil the milk without spillover, it is considered that the stove and cook are good, in controlling the fire power.

I have discussed a lot about the simmering phase in my two publications. Those who are interested can access the paper through the following links.

1.    http://www.sciencedirect.com/science/article/pii/S0360544214005325

2.    http://www.sciencedirect.com/science/article/pii/S0360544214003417

In the second link, you may find a short presentation about the study (next to the highlights)

With Best Regards,

P Raman, Ph.D

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