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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='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear Nolbert<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>You have raise a very important point that is relevant not only to your work and field experience, but it stove evaluation in general and to CREEC’s work in particular plus it is directly relevant to the IWA.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:#1F497D'>>…</span></b>i have experienced for the last 2+ years how economical in terms of wood consumption (therefore wood saving) TLUDs are in this region.<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>That is very good news. I have no problem with that, meaning I see no issues with TLUD’s saving fuel. They should because they operate (usually) with a low excess air (EA) level and therefore have an inherently better heat transfer efficiency. There are two main thermal gains from a TLUD: better combustion efficiency (burning all the fuel) and lower EA levels. The more EA, the lower the efficiency. It is important to document the actual fuel use reductions, or fuel switching if that is relevant. As has been pointed out many times here, fuel switching is often more important than saving kilos of fuel because there is waste biomass lying around.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='color:#1F497D'>></span>Lab tests at CREEC (Makerere University) have also proved that TLUD micro-gasifiers are efficient backed with statistical data, including PEMS tests and comparisons with other types of stoves like the classic charcoal burners, rocket stoves and of course the 3-stone.<span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>This is the important part: “</span>Lab tests at CREEC<span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>”<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>They are using the WBT, right? They are stating the following: according to the WBT’s conducted, “the calculated specific fuel consumption of the TLUD is xxx and the calculated specific fuel consumption of the other stove is yyy”. Is that pretty much the say the result is given?<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The WBT makes use of a metric called the Specific Fuel Consumption. As has been pointed out at the IWA and in several other places and letters and comments, the SFC is <i>not</i> the fuel consumption. It is a number calculated from the energy used to calculate the thermal efficiency. I hope you can follow this because it is well-hidden in the math of the WBT and is why I make so much noise about this ruinous relic of stove testing’s past. The EPA webinar presented by the SeTAR Centre a couple of weeks ago covers this point as well:<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The WBT calculates first the thermal efficiency. v.4.1.2 does a much better job in this regard that UCB-WBT 3.0 did. So when the calculation is done, the energy used to do the cooking is calculated, including deducting for the energy that remains in the char. What wood gases are burned, and what carbon was burned, are calculated to be the heat energy given to the pot, some of which gets into the pot. The efficiency with which that transfer is made is the heat transfer efficiency. If it is detected using the water temperature only (as per WBT 4.1.2) or the pot and water temperature (as per the Indian WBT) you get a net heat transfer efficiency which is always lower than the actual heat transfer efficiency. No problem.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The energy used during cooking is then divided by the Dry Fuel energy content, let’s say 18 MJ/kg. That yields a Dry Fuel Equivalent of the energy used to make the thermal efficiency calculation. It is <i>not</i> the mass of fuel used to do the cooking, nor is it the dry mas equivalent of the fuel used to do the cooking, it is the dry fuel equivalent of the net energy liberated, as calculated for the determination of the thermal efficiency.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The point that Kevin raised is very important: if the char produced by the stove during the cooking is not useable in the that same stove, then it is lost. It can be lost to a biochar project, it can be lost to a charcoal stove, it can be lost to the ground around the house, it does not matter. But it was used by the stove during cooking.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Now consider: suppose a stove produces a lot of char and you use the WBT 4.1.2 to calculate the ‘specific fuel consumption’? That is the dry fuel equivalent divided by the number of litres of food cooked (well, in the case of the WBT 4.1.2 it erroneously uses the mass of food remaining in the pot, not the actual mass but that is a quibble). The point is the stove comparison is not made using the actual fuel consumed, it uses the dry fuel equivalent per litre calculated from the energy efficiency formula. If a stove uses 1 kg of fuel each time it is lit, and it produces (as a left-over) char with a mass of 100g, and that 100g is not used the next time the stove is run, then the consumption is 1 kg. Simple as that. You cannot credit char number to a stove for fuel consumed unless it is used. The most extreme acceptance would be that the next time the stove is lit, that char is going to be burned in it. If it cannot, or does not if you are paying attention to social behaviour, then that stove cannot be credited as ‘not having burned that portion of the fuel’. It did not burn it, but it <i>consumed</i>. Saving fuel means not consuming fuel.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The implication for CREEC and for anyone else using the WBT 4.1.2 is that the stove fuel consumption comparisons are not valid measures of the fuel used (consumed) by the stove each time it is lit. This error is not large when burning relatively dry fuel and the char mass remaining is small. But in the case of TLUD’s producing char, the WBT number is <i>very</i> misleading.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The fact that the TLUD’s you see are saving fuel is valuable information, provided the measurement is made of fuel being taken from the forest, and not the result of a misleading interpretation of fuel consumption as is embedded din all of the UCB-WBT tests and its derivatives. The error is huge, like 70 or even 80%. The example of the Namibian stove given in the webinar shows an error of 40% for a modest stove producing 20% char, which that stove actually does. <o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>That stove won awards because the ‘test result’ was ‘so good’ but in fact it saves nearly no fuel at all compared with an open fire. That is the problem with these wretched WBT’s with defecting concepts embedded in them.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='color:#1F497D'>></span>These stoves are using less wood, cooking faster which is a major reason for their acceptance in East Africa. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Good combustion, low EA.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='color:#1F497D'>></span>Women in the kitchens have tried and experienced how they use less quantity of wood, are less smoky and also cook quicker than their current conventional stoves.<span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Ditto.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='color:#1F497D'>></span>The notion of making char is a plus for TLUDs because they use the char for other valuable purposes including cooking.<span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Interesting as long as it does not increase fuel demand, in my view. That char comes from raw fuel not burned.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='color:#1F497D'>></span>If you think otherwise, then you should try personally using these stoves for a while to prove what we are experiencing here.<span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I have built and tested lots of stoves including TLUD’s. You can see one in the stove library called the Grasifier – a $1 stove made from sheet metal, originally designed for Haiti, burning switchgrass pellets.<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Best regards<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>PS Kevin I would appreciate your input on the subject.<o:p></o:p></span></p></div></body></html>