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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'>Dear Ranyee<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>For those who may be new to the metrics involved I will add just a little on one point you raise in explanation (and thank you for that).<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>></span><span lang=EN-US>The IWA metrics do not include emissions per mass of fuel used.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>For some this may seem odd as a lot of the US regulations state emissions per kg burned. When the emissions are measured per unit of energy (usually per MegaJoule) the number becomes ‘translatable’ or ‘portable as I like to call it. If you have an emission per MJ then if you know the energy content of any fuel means it is a simple matter to make the conversion to emissions per unit mass (just divide the emissions number by the net heat energy per kg or per pound).<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>On the other hand, if you are given the emission per kg and do not know the energy content of the fuel, you cannot make the translation back to ‘mass emitted per MJ’. <o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>For this reason, it is wise to always report things per unit of energy so anyone can make use of the number in their local methodology.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>Lately we are seeing reported the ‘emission per net energy delivered’. There is great utility for this in the stove community. If you have the emission mass per MJ delivered into the pot, or pots, or the room if it is space heating, you have a metric that can be used to make a direct comparison between different stoves and fuels without having to do any conversions at all. <o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>It a stove emits 10 mg PM 2.5 per MJ and the thermal efficiency to the pot is 35%, then the emission per Net MJ is 10/0.35 = 28.6mg/Net MJ<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>A different stove emitting 14 mg PM2.5 per MJ with a heating efficiency of 49% is:<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>14/0.49 = 28.6mg/Net MJ which is exactly the same amount of PM 2.5 to do the same cooking task (at that power level).<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>Thus if you are comparing two stoves one of which emits 14 mg and other 10 mg per MJ of heat from burning the fuel, it is misleading unless you also consider the efficiency of heat transfer as well. The two are combined by reporting the emissions per net MJ of heat delivered.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>Some national standards use the net heat delivered as the denominator in the equation but is it relatively uncommon.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p></div></body></html>