[Stoves] Global Alliance for Clean Cooking Stove catalog

Crispin Pemberton-Pigott crispinpigott at outlook.com
Thu Jun 5 16:07:09 CDT 2014


Dear Erin

 

Thanks for that link

 

http://catalog.cleancookstoves.org/#/stoves 

 

Regarding the emissions and metrics: It will be in interest to the stove
community know that some consideration has been going on behind the scenes
and on this list for years about what metrics are the most useful to report.
There is not yet full agreement so I am bringing it forward again as
something that needs work:

 

This is the list at the bottom for an Oorja Stove from India



 

Note that the emissions of PM are given as BC (black carbon) per kg burned,
PM2.5 per kg of fuel burned and PM2.5 per minute.

 

I find this PM mass per kg burned almost uniquely American in that the EPA
started off giving emissions per unit of mass and everyone copied that, at
least among the early adopters. Not sure really where it started, but it is
misleading as we have discussed several tiems before.

 

The problem is that the numbers are not useful directly unless you know what
the kg of fuel was, and a comparison cannot be made with other fuels unless
a conversion is made first to get the heat content normalized, and then to
incorporate the system efficiency (not the heat transfer efficiency).
Because the system efficiency is not reported, it means from the above
numbers, one cannot get the most practical metric from the list (because
some info is missing).

 

A stove is used to cook, and people burn the fuel until the cooking is done.
If the heat transfer efficiency is poor or the stove wastes a lot of fuel
(making leftovers that are not useful in the next fire, for example) then
the amount of PM emitted will be high 'per useful MJ' but not necessarily
'per kg'. In short, one cannot tell if the total emitted to cook something
is higher or lower than for another stove.

 

If a stove a) burns all the fuel put in it, b) has a high heat transfer
efficiency and c) has a lower mass of PM emitted per useful MJ of heat then
we have something that can be compared across the board: any stove, any
fuel, anyplace. All you need to do is plug in your burn cycle.

 

So if you can report the mass of BC and PM2.5 emitted per useful MJ
delivered to the pot, you have the analogy for emissions smoke per unit or
per task of 'cooking'.  

 

The most useful metric is PM2.5 mass per MJ(net) accumulated in the pot.

 

I say 'net' because heat transferred that is lost from the sides is not
accumulated. If you were perfectly simmering, all heat gained by the pot
would be lost from the sides in which case there would no net gain (no
change of enthalpy). When 'boiling' this same process is going on it is just
swamped by the gain of heat in the water and food, but it is still there. 

 

It is the net heat gained by the pot that is useful cooking energy. As
people will, say, boil 5 litres of water, it takes about 1.8 MJ each time in
the pot. How much PM is emitted per kg is not nearly as important as the
emissions per MJ. You get my drift?

 

Thus when comparing the emissions we are interested in two numbers for PM:
The mass emitted per MJ delivered, and the rate of emissions into the room
(which is the last number on that list). Depending on the kitchen
architecture, that rate sets the smoke concentration in the room if it is an
open fire type device (no chimney).

 

Apart from checking the validity of the metrics, we should investigate the
underlying assumptions about how the number will be used to make
comparisons. 

 

Regards

Crispin

 

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