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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 Frank<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'>></span><span lang=EN-US style='color:#1F497D'>It takes </span><span lang=EN-US style='color:#1F497D'>[Joules of]</span><span lang=EN-US style='color:#1F497D'> energy to go from 20c to 100c and from 100c liquid to 100c vapor. </span><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'>Correct.<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'>></span><span lang=EN-US style='color:#1F497D'>But doesn’t it also take in more energy when water vapor is heated from 100 to 450 (?) </span><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'>Also correct.<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'>>…</span><span lang=EN-US style='color:#1F497D'>and that is removed before it is used for work?</span><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'>The ‘work’ is heating the pot and that drops the temperature of the gases and vapours. At some point the gases are pretty much ineffective at raising the temperature of the outer skin of the pot so it is literally wasted.<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 good example to think about is a gas oven for firing ceramics. It produces a huge amount of heat, and the temperature of the flame is high, but they are very inefficient. The gases pass out of the furnace at about the temperature of the inside. If you are firing to 1100 C then the wasted gas is >1100 coming out. That is an enormous loss. A gas oven is only about 18% efficient at that temperature! Electric ovens are much more efficient, but you have to generate the electricity first. Turning gas into electricity at 50% efficiency then feeding it into electric elements uses less total energy.<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 stove is akin to a kiln. There is always a loss because the pot when boiling is never much below 100C at habitable altitudes. The convention is to use LHV (lower heating value) as the measure, assuming that heat below 100C is always going to be wasted. <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 heat it takes to go from 0 to 20 to 100 is for some reason not included in the calculation, just the latent heat of evaporation. I believe it is for simplicity and convenience. It is not exact but the error is small – typically 60,000 Joules per kg of biomass (0.06 MJ).<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 small measurement error in fuel moisture has more influence than that dose of energy.<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>