[Stoves] Back into action

Tue Sep 12 12:06:53 CDT 2017

Dear Frank,

Thank you, sincerely, for exploring ways to improve protocols, for frankly discussing about ways to solve the problem. This is the discussion that needed to happen.

« Do you think they will come out the same? That the time it takes, the amount of fuel used, the PM2.5, quality of finished food,  etc. etc. 

When all the variables are controlled. »

I don’t know. In the case you describe, are all the existing variables really controlled?

But what you say seems plausible.

Not being an engineer or a researcher, I cannot tell.

Engineers or researchers, for example on this List, could answer that. Their answers will have to be backed by good arguments, and if they conclude that the protocol you mention is scientifically valid and allows for a good prediction of the performance on the field, then I might be convinced. If I am convinced, I will support that.

If I am not convinced and major issues remain to be solved, then I will recommend against it.

Just like I did for the WBT.

The question would also be: would your protocol allow to solve the issues of the WBT, and how:

·         « the (WBT) protocol prescribes to test the stove for a fixed combination of burn sequence (high-power and low-power) and pot dimensions. This limits the test relevance to just that particular setting: when any variation of these parameters which deeply affect the system performance is introduced, results may significantly differ.

·         uncertainties related to temperature reading and vaporisation in the boiling region lead to high variability between test replicates. In order to improve the reliability and replicability of the tests, the latest version of the protocol includes the section “Changes to Testing Conditions to Improve Repeatability”, which refers to different fuels and pot characteristics. However, eventual changes involving other parameters (pot insulation and maximum water temperature), which deeply affect test variability, are not mentioned. Such problems give evidence of an unsolved conflict between the declared purpose of the WBT (viz. to be a design-phase test, not intended to be representative of real-use performance), and a general tendency to use the results form WBT as a significant means to select the most appropriate cooking stove for a given context. A lot of debate has been made around formulation of metrics, primarily on thermal efficiency (Table C3), which is often interpreted as the most immediate and distinctive stove performance parameter. Studies from Bailis et al. highlighted how relying on WBT thermal efficiency outputs, regardless of the relative importance of high and low power cooking tasks among the target population, can lead to misleading interpretations. Furthermore, Zhang et al. and Jetter et al. questioned the scientific meaningfulness of thermal efficiency at simmering. Indeed, this phase is characterised by highly variable steam production, which represents a heat loss in the energy balance but positively contributes to the efficiency value in the actual formulation of thermal efficiency.

·         Finally, some unsolved issues concerning statistical significance of data are worth mentioning. WBT 4.2.3 includes “Statistic Lessons for Performance Testing”. The appendix specifies that the minimum number of test replicates for each model of stove should be three, although it is reported that this number of replicates is not necessarily sufficient to determine a stove performance within a certain confidence interval."

If the chosen cooking task include boiling, wouldn’t it be a problem? Does boiling means the same for an American master student in engineering and an Indian cook?

Would your protocol work also with a Rocket Stove?

Thanks again for being willing to discuss technical questions on alternative protocols.

Best,

Xavier

De : Frank Shields [mailto:franke at cruzio.com] 
Envoyé : vendredi 8 septembre 2017 16:59
À : Xavier Brandao
Cc : Discussion of biomass cooking stoves
Objet : Re: [Stoves] Back into action

Dear Xavier,

A single Question:

If, for example, Paul Anderson sent a Champion TLUD to the lab along with a bag of pellets. And also sent stove and pellets to a Receiving Community. And they were instructed to do the following:

1) Make sure pellets are certified for US certification to meet the same specs.

2) Fill the stove with pellets, tap three times then fill to the line.

3) Both combustion chambers (stoves) are the same

4) use the same utensils

5) cook the same way

6) complete a similar task determined by an agreed upon measure

Do you think they will come out the same? That the time it takes, the amount of fuel used, the PM2.5, quality of finished food,  etc. etc. 

When all the variables are controlled. 

If you answer Yes - that is proof the system (can) work. 

If you answer No - then Cecil please take over. 

If the labs that were doing the testing goes out of business or changes to testing something different due to lack of work and we loose them. We will then be really starting over when we come around to needing them. 

If you answer Yes to above then we need to start finding ways to control the six groups of variables.

There is no jumping ahead to the field, no shortcuts. We need to do the work. 

Regards

Frank 

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