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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Dear Paul<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'>Sorry if anything was confusing.</span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>1. This is an extremely slow burning stove. Consistent, yes. But it lacks fire power. <span style='color:#1F497D'><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'>Hang on, there are many such small applications which require that amount of firepower, max. See below.<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>And it should therefore be compared with other small stoves.<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Absolutely agree. The smallest stove I ever saw (apart from heating vegetables at the Holiday Inn) was in Senegal. It is a tea making stove for night guards. It looks like a tiny ceramic lined Jiko. I thought it was an advertisement, a model, when I first saw it!<o:p></o:p></span></p><p class=MsoNormal><br>2. I am concerned about the comment<br><br><span style='font-size:12.0pt;mso-fareast-language:EN-CA'><o:p></o:p></span></p><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal>ignoring the first 16 minutes during which the fire was getting established. <o:p></o:p></p></blockquote><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I am referring to the average thermal efficiency. It was 29% over the first 16 minutes and completely consistent after that (well over 50%). So I used for the cooking power plot the average of the latter 7/8 of the test, ignoring the 29% average for the first 16 minutes. I didn’t tweak the time selection to see when the high average efficiency number kicked in.<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'>So…if I ignore the first 9 minutes, the average in that time is 10.2% and the average for the rest is 57.8%. So, I can use the figure 57.8 instead of 59.6 (the original number). There is no visual difference on the chart. <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>That delay alone could mean rejection of the stove by users or in testing situations.<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>That is a misunderstanding. There is no delay in lighting, I was talking about where I got the average efficiency number. As you can see from the chart, the full power level was achieved after about 7 minutes from ignition.<o:p></o:p></span></p><p class=MsoNormal><br>3. More details are requested: <br>Size of pot (especially the diameter of the bottom), <br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>There was no pot involved. I used a pseudo pot to prevent outside air diving into the combustion zone. The cooking power is calculated, not measured.<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>Small stoves are not designed to boil 5 liters, so 5 L is unfair to such stoves with low power.<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Obviously. This stove would be suited to cooking 1.5 litres – a single person’s food. In fact it is likely to be used for applications such as making batiks (turned well down to less than half power).<o:p></o:p></span></p><p class=MsoNormal><br>4. 57% cooking efficiency (capture of the heat) is wonderful. But <b><i><u>IF </u></i></b>it is only able to keep a baby's bottle of milk warm for over 80 minutes, the usefulness needs clear statements when describing the stove. <span style='color:#1F497D'><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'>450-500 watts of cooking power is far more than is needed to keep something warm. Slamm kerosene stoves have a firepower of about 1.1 kW and a thermal efficiency of about 40% which is only 450 watts and they are bought in hundreds of millions.<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>On this Stoves Listserv we are accustomed to "standard size stoves for a typical meal" and the use of 5 liters of water in the pot, so we run the risk of equating stoves that are really in very different categories by size. <span style='color:#1F497D'>…</span><br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Well, the talk is like that but the situation in the field is different – certainly in urban areas where a majority of stove buyers live.<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>5. On the same note, but at the other extreme, the institutional stove by InStove (60 liter capacity pot, I believe) was proclaimed several times at the Ghana GACC Forum about its attainment of Tier 4 status. <span style='color:#1F497D'><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'>I am unimpressed by such claims, to be frank. First, three of the metrics have no physical basis so achieving ‘Tier 4’ status on those means nothing real. To get a useful number you have to have the raw data from the spreadsheet and remove the division by the water mass remaining to get the ‘total’ number.<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'>Next, as shown in the discussion of the Two-stove performance calculation, the thermal efficiency does not tell you what the fuel consumption is, so what is the Tier 4 fuel consumption per task completed? No one knows. It could be 25% of 50%.<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>That is great!!! <span style='color:#1F497D'><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'>Sure, we can conclude that it is ‘better’ but not much beyond that.<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>But all should know that using larger pots and more water do greatly impact the results of stove testing. As Dean Still said in his Saturday night keynote presentation at ETHOS 2015, he accomplished some Tier 4 ratings by shifting to a pot with 9 liters instead of 5 L. <span style='color:#1F497D'><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'>Otherwise known as ‘gaming the testing system’. It is damning evidence that the WBT is not useful for comparing stove performance ratings.<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>He did acknowledge that he had gamed the system but was within the rules, so it was not cheating. <span style='color:#1F497D'><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'>Volkswagen was also working within the rules. Every car with that type of engine passed the test. If owners never put their foot to the floor, their car never emitted ‘too much’ NO. Yet people are upset!<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>After ETHOS while at Aprovecho's Open House, Sam Bentson (co-author with Dean) and I and others discussed several ways of how to game (distort) the testing system. But the promised summary of such methods was not prepared (or at least not released). Maybe it will eventually be presented. <br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>When writing national standard test methods, we spend a lot of time thinking of ways to cheat the test, or evade it ‘legally’ and then write the text to close every loophole we can think of.<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>This is done by keeping an eye on what the test is supposed to be demonstrating, which for wood stoves in developing countries is emissions and fuel consumption per year (etc). By having a correct concept of the purpose of the test, one arrives at a method of testing all stoves as fairly as possible. The big difference between small solid fuel burning stoves and power stations is the fact they are started and stopped so frequently. This requires a new approach.</span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>At the moment we are discussing in China when to end the test and what rules could be used to include the burn-out emissions (which are real and in the home or neighbourhood) and which continue long after the cooking (or test) sequence has ended. How long should we measure PM emissions after the formal test has ended? Eight hours? Twelve? Until it ‘stops’?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman",serif;color:#1F497D;mso-fareast-language:EN-CA'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-CA'>Not so simple.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-CA'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-CA'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-CA'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D;mso-fareast-language:EN-CA'><o:p> </o:p></span></p></div></body></html>