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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-US'>Dear Erin<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-US'>Thanks for that link<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US><a href="http://catalog.cleancookstoves.org/#/stoves">http://catalog.cleancookstoves.org/#/stoves</a><span style='color:#1F497D'> </span><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>This is the list at the bottom for an Oorja Stove from India<o:p></o:p></span></p><p class=MsoNormal><img border=0 width=473 height=184 id="Picture_x0020_1" src="cid:image002.jpg@01CF80E0.8C342150" alt="cid:image002.jpg@01CF80E0.8C342150"><span lang=EN-US style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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).<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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 <i>per useful MJ of heat</i> 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.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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’. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>The most useful metric is PM<sub>2.5</sub> mass per MJ<sub>(net)</sub> accumulated in the pot.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>It is the <i>net</i> 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 <i>in the pot</i>. How much PM is emitted per kg is not nearly as important as the emissions per MJ. You get my drift?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>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).<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Apart from checking the validity of the metrics, we should investigate the underlying assumptions about how the number will be used to make comparisons. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p></div></body></html>