[Stoves] Irrelevant lab testing - for what purpose?

[Crispin Pemberton-Pigott]

Dear Frank

I want to share one of the problems associated with boiling water as a method of testing a stove for regulatory purposes.

In order to have a replicable output come from a set tests, one has to establish rules. One would be that the fuel properties are known (moisture content, heat content). Another is that the scale and temperature equipment is calibrated.

With ‘boiling’ there are numerous problems<http://www.sites.hps.cam.ac.uk/boiling/>.  The boiling point of water is a big enough problem, but choosing when water ‘has boiled’ is a subjective matter and not suitable for a scientific investigation.

First we should look at what information has been requested. What is the question? What are the measurement needed to answer that question? What metrics are to be used when reporting the answer?

Nikhil and other are suggesting that we have been asking the wrong questions, or that we should have asked additional questions. I agree that the questions asked are too few. The way the answers were determined was defective, giving answers that were sometimes spot-on and sometimes seriously misleading. Key in that has been, to date, the WBT because it is poorly constructed (compared with, say, a test for a power station or steam boiler).

The serious issues we face, as a group, with poor field performance compared with lab test claims, is definitely rooted in the WBT in its various forms. It is clear that those responsible for creating and maintaining and editing over the past 15 years are not going to fix it. They would have done so long ago if they were serious. They are in ‘batten down the hatches and ride out the storm until the ISO standard is in place’ mode. Correcting it now is an admission that there was something (several things) seriously wrong with it all along. Instead, we hear endlessly about how lab tests are not really supposed to tell us how a stove will perform in the field – that requires a different type of test. Huh?

So why is boiling water such a problem? Because it depends on too many variables. The pot condition changes the boiling point. So does the atmospheric pressure. So does the water composition. And ‘when’ is a point boiling? When I say so or when you say so?

Why is there any interest in ‘time to boil’? TTB we can call it. TTB is a measure of the heat gain rate of the pot. Changing the pot or the mass of water in it changes the time to boil. What we want to know is the heat gain rate. If I know the heat gain rate from any stove+pot I can calculate the TTB for any mass of water I wish. The heat gain rate is the underlying metric that yields the time to boil 5 or 3 or 1.5 litres.

You can get the heat gain rate without boiling any water at all. It is a feature of the system. It is also surprisingly constant in terms of the efficiency. If you correct the mass change of a fire for the composition of what is burning, you get the actual fire power available at the time. It can easily be shown that the heat transfer efficiency is surprisingly constant during ignition, much more than is often assumed. The same is true for late fires when the char is burning. So the interesting metric is the heat gain rate maximum, or 5 minute average – whatever you want to know. It is not accurately found by boiling water subjectively, it is found by measuring the rate of change of the water temperature which is an easy and accurate thing to determine. Everyone will get the about same number.

A water heating test WHT is more useful in characterising a stove’s capabilities than a WBT precisely because it does not involve boiling the water.

Regards
Crispin


Nikhil,

Dear Nikhil, Stovers,


There are lots of stove developers out there that would like to have their designed stove in the running. We need a way to include all of them or we miss out on some great ideas. Going into the field is expensive and takes a lot of people. The lucky stoves chosen for the study is picked by what means? And are they the best stoves for the location? and available fuel supply?  A fair method for choosing the stoves taking to the next step (field) is needed. Lab testing is relatively cheep and used for this purpose.

The only part of real world we lab people need to mimic is the energy supply that does the work. The other parts of the 6-Box system is any representative task where we have control over the completion.

Using pellets or processed lumber fuel is not a good mimic of the real world variable wild biomass. I’m thinking the percent of the biomass producing pyrolyzed gases in N2 environment is a good measure for the energy going to the secondary. Most important is that it can be specific to each biomass and easily and reproducibly determined. We can then (if this works) predict the best stoves for an area.

When you think of the different biomass used for fuels like briquettes, dung, coal, wood, corncobs, pressed biomass, rice etc.etc. this method can be used across all of them.

We use boiling water as a task. We could use rice but we introduce a couple more variables. What kind of rice and when (exactly) is it called ‘cooked’. We could use boiling carrots cut to specific size and a penetrometer. We could add sawdust to the water to represent soup. What to you suggest other than water?

Once we  get the selection of stoves for an area (that use their fuel and cooks their food) we can make the next level of selection. Do they need fuel savings? is air quality an issue? what fuel prep is required to prepare to work in the stove, etc.

The lab is needed to get all those that wants to into the game. Its affordable and create a list of stoves that have a good chance of working at a specific site.

If we introduce a list of workable stoves to the people and let them pick I think there will be less contamination of the receiving site from our influence.  Not happy with the stove they picked then they should have picked a different one.


 Frank







On Jun 4, 2017, at 10:19 AM, Nikhil Desai <pienergy2008 at gmail.com<mailto:pienergy2008 at gmail.com>> wrote:

Frank:

How does what you propose mimic "real world"?

And whatever made you think boiling water is a representative task around all users?

Time to stop boiling water and fussing over energy efficiency with some standard fuel, standard cook, standard cuisine.

I do like your idea of a "spider graph". Why can't we design 10 or 20 such spidergraphs for any particular region for permutation and combination of actual fuels, stoves, and different metrics than energy or char outputs? What is this theory that a cook wants to maximum energy utilization out of a supposedly free fuel?

Nikhil


------------------------------------------------------------------------
Nikhil Desai
(India +91) 909 995 2080
Skype: nikhildesai888



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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