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Dear Frank</div>
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Efficiency is one of the most highly reproducible metrics if measured and calculated properly. Getting a good result requires having a good conceptual framework. </div>
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James Robinson and I have tested stoves with 5 point each at high, medium and low powerý. In some cases the dots on the chart overlapped. Those were small stoves so size is not the issue. </div>
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There is no good reason to assume that a stove tested in a lab will now, on average, perform the same as in the field. To accomplish that requires knowing what people do in the field. What we do is get Cecil' observations and replicate the rural cooking beside
the lab. Focus groups discuss if that is how people cook and operate the stove(s). The overall performance is captured by the lab equipment so we get the performance during different cooking cycles. </div>
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We are all aware that WBT results are quite variable. There are several reasons, some conceptual and some mathematical and some operational. This has been confirmed by Marcello Gorritty in his 2014 review of more than 600 tests, and by Fabio Riva in 2016 who
looked at the results and the statistical treatment of three test sets vs five. </div>
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<span style="font-size:initial; text-align:initial; line-height:initial">>From what I hear on this list and other discussions, there seems to be a general feeling that stove tests are not reproducibleý the way other device tests are. There is a low expectation
that lab tests will match field performance. Strange. Why is the lab test not replicating what people do in the field? What is the point of a test that doesn't? </span></div>
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<span style="font-size:initial; text-align:initial; line-height:initial">Regards </span></div>
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<span style="font-size:initial; text-align:initial; line-height:initial">Crispin </span>
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<div>Dear Crispin,
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<div class="">I understand what you are saying but can that be done with these small ever changing little stoves? I can see it working for large systems with controlled fuel, controlled insulation for holding in the heat, controlled air intake etc. You can
dial in the efficiency from calculations. But these small stoves have so many uncontrolled variables and we need a predicted curve as the flame goes from hot to smoldering etc. If we can’t get predictable efficiencies as the combustion goes through changes
and are able to plot them and average under the curve - then we can’t use efficiencies. And it must be reproducible within limits if we want to be able to assign a stove a value. And with just the fuels being different (moisture, particle size, carbon densities
etc) I don’t see that being done. Isn’t that the real problem we have been having for years? Trying to assign efficiency values when it can’t be done because of all the uncontrolled variables? </div>
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<div class="">And just putting stoves in the field and seeing what people like is no better. Thats what they have been doing for years already. If you find some dirty ones do you say they can’t use them? They need be replaced with clean ones - without having
a system to list the clean ones they can pick from? </div>
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<div class="">I would be very surprised if we find a biomass that when tested in two stoves and one is shown to be twice as efficient to actually use half the fuel. We are talking the heat calculated from the fuel that goes into the water - correct? </div>
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<div class="">I’m thinking of a graph like below where we test many parameters of the biomass and plot them. Fixed carbon, moisture, carbon density, particle size, ash, particle shape, lipids & resins and a few more. The stove is fitted on the square where
it works best. i have no idea how to do it but I am sure you and others do. The needed test data and method i have a lot figured out. We need a new approach. Regards</div>
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<div class="">Frank</div>
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<div class="">On Feb 5, 2017, at 10:47 PM, Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@outlook.com" class="">crispinpigott@outlook.com</a>> wrote:</div>
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<div class="">Dear Frank<br class="">
<br class="">
Efficiency is important because it is related to the consumption of fuel. If a stove is twice as efficient it will use half the fuel.<br class="">
<br class="">
In Bishkek at the moment the stove being field tested is three times as efficient as the baseline stove. Therefore it uses 1/3 of the fuel to deliver the same amount of energy (heat).<br class="">
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If two stoves with the same efficiency are rated differently, that will mislead the public. If a defective method used rates ten stoves as different when in fact they are the same, ýthe method has to go, not the mis-rated stoves.<br class="">
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Regards<br class="">
Crispin<br class="">
<br class="">
<br class="">
Dear Stovers,<br class="">
<br class="">
Why is knowing the energy efficiency so important?<br class="">
<br class="">
If we were to take a tin metal stove and provide a controlled heat source (oxygen-acetaline) and measure the energy efficiency at different, steady powers (say 1/4th, 1/2, 3/4 and full power) using the WBT as indicator this would not likely be a straight line
- I am thinking. Then take a well insulated clay stove and the four points would likely be more of a straight line but all stoves would have a different curve.<br class="">
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Now add a controlled fuel like propane (with no O2 source) and now you add to the variables primary air and secondary air. Then switch the test to using biomass and more variables are added.<br class="">
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I’m thinking without a straight (or at least predicted) curve for the four power settings regarding energy efficiency that the test is meaningless. There is no good value for a stove for energy efficiency. No reason to go all out for that value.<br class="">
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I’m thinking a better approach is Fuel Classification vs Heat into the Pot. I think using a single type of biomass fuel we can predict the time it takes to boil the water. Use another type of fuel and it takes a little longer - every time. The difference is
not the energy in the biomass but more the Classification we give to the biomass. (still needing development). We test success using Cecil approach to find out how well it works - but know from lab study the biomass properties so to be able to compare and
predict success in different locations.<br class="">
<br class="">
Regards<br class="">
<br class="">
Frank<br class="">
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<br class="">
Thanks<br class="">
<br class="">
Frank<br class="">
Frank Shields<br class="">
Gabilan Laboratory<br class="">
Keith Day Company, Inc.<br class="">
1091 Madison Lane<br class="">
Salinas, CA 93907<br class="">
(831) 246-0417 cell<br class="">
(831) 771-0126 office<br class="">
<a href="mailto:fShields@keithdaycompany.com" class="">fShields@keithdaycompany.com</a><br class="">
<br class="">
<br class="">
<br class="">
franke@cruzio.com<br class="">
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</blockquote>
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<div class="">Thanks</div>
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<div class="">Frank</div>
<div class="">Frank Shields</div>
<div class="">Gabilan Laboratory</div>
<div class="">Keith Day Company, Inc.</div>
<div class="">1091 Madison Lane</div>
<div class="">Salinas, CA 93907</div>
<div class="">(831) 246-0417 cell</div>
<div class="">(831) 771-0126 office</div>
<div class=""><a href="mailto:fShields@keithdaycompany.com" class="">fShields@keithdaycompany.com</a></div>
<div class=""><br class="">
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<div class=""><a href="mailto:franke@cruzio.com" class="">franke@cruzio.com</a></div>
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