[Stoves] Energy efficiency value

Mon Feb 6 05:03:15 CST 2017

Dear Frank

Efficiency is one of the most highly reproducible metrics if measured and calculated properly. Getting a good result requires having a good conceptual framework.

James Robinson and I have tested stoves with 5 point each at high, medium and low power‎. In some cases the dots on the chart overlapped. Those were small stoves so size is not the issue.

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.

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.

>From what I hear on this list and other discussions, there seems to be a general feeling that stove tests are not reproducible‎ 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?

Regards
Crispin

Dear Crispin,

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?

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?

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?

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

Frank

[... dash and gap patterns more fill patterns for bar charts and area plots]

On Feb 5, 2017, at 10:47 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:

Dear Frank

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.

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).

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, ‎the method has to go, not the mis-rated stoves.

Regards
Crispin

Dear Stovers,

Why is knowing the energy efficiency so important?

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.

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.

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.

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.

Regards

Frank

Thanks

Frank
Frank Shields
Gabilan Laboratory
Keith Day Company, Inc.
1091 Madison Lane
Salinas, CA  93907
(831) 246-0417 cell
(831) 771-0126 office
fShields at keithdaycompany.com<mailto:fShields at keithdaycompany.com>

franke at cruzio.com

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to UNSUBSCRIBE or Change your List Settings use the web page
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Thanks

Frank
Frank Shields
Gabilan Laboratory
Keith Day Company, Inc.
1091 Madison Lane
Salinas, CA  93907
(831) 246-0417 cell
(831) 771-0126 office
fShields at keithdaycompany.com<mailto:fShields at keithdaycompany.com>

franke at cruzio.com<mailto:franke at cruzio.com>

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