[Stoves] How other tests calculate with remaining charcoal ... was Re: Advocacy action: ask the GACC to stop promoting the WBT

Sun Jan 22 21:16:16 CST 2017

Dear Paul

As far as I know, in general all tests of thermal performance such as power stations, fixed boilers, heating stoves and cooking stoves in the formal sector treat solid resides with energy content remaining as a 'mechanical loss'. That is the definition of a mechanical: unburned fuel that could in theory have been burned ‎but was not, and is left at the end. The exceptions to this, in terms of rating the thermal efficiency, are the WBT and it's derivatives such as the Enhanced Precision Test Protocol and it's later evolution.

The 1982 test devised by Bois de Feu (I just checked) ‎used the same deduction however they did not call the metric the thermal efficiency, because it is not the thermal efficiency. They called it the Percentage Heat Utilised. PHU was still a popular term when I joined the stove list. The VITA test used the term before and after modifications by Baldwin.

It a technically correct PHU calculation is made, which would include counting all the energy in the solid residue, not just the 'recoverable' portion of it, it is the same as the heat transfer efficiency.

There is an excellent chart of heat flows from the fuel fed to its intimation destinations in the Zhang Y 2014 paper. I posted it to this group some months ago. ‎You may recall Prof Lloyd complimenting it. The students spent a long time on that getting it complete and sectioned to serve as a guide for designers of test methods. Any energy in the residual char comes in two parts: unburned fuel, and heat in the mass. The ash is very hot when it is pulled out of a big boiler and this is accounted as well (the list is comprehensive!)

As to the reporting of char production as a conscious act, which is what I think you are looking for, this is handled in two ways, ‎mass produced over mass of fuel (wet or dry as you choose) and then the energy content over the fuel energy (wet or dry). All of these are % values and there is nothing subtracted from the denominators.

In order to decide on a calculation you have to be clear on what you want to report. Is char a benefit? Is it a benefit for this same stove? Is it a benefit for a different stove? Is it a benefit ‎as biochar to bury? Is it a benefit as sequestered carbon?

Is the energy in the char a benefit? That implies the fuel mass is really a proxy ‎for the energy in it so the questions are: is it fuel energy for this stove or another one?

Nurhuda's stove that makes then burns char simply divides the fuel into two portions and burns it almost completely so it is fair to evaluate it as a single burn even though it has two clear, separate combustion periods and hardware.

It would not be appropriate to 'elevate' the cooking efficiency by deducting the char energy from the fuel energy fed in during the first portion, and then in addition, add the energy delivered to the pot from the char divided by the char energy. That would give a really erroneous overall rating.

‎So, how would we approach the same situation when the two sections of the overall cooking were performed on different stoves? The calculation should be identical but not added together because now there are two different stoves to rate.

If you are not trying to calculate the heat transfer efficiency, there is no subtraction from the fuel ‎energy in the denominator. No one rating and comparing fuel consumptions needs or wants to know the heat transfer efficiency because that is an internal metric that is not considered because it does not cross the box encompassing the combustion system.

The PHU metric is not the same as any normal calculation of the thermal efficiency because it only considers part of the energy in the residue. It certainly does not represent the fuel consumption which is my main point. Changing the name didn't improve the calculation and doesn't make it relevant to fuel savings nor the values of char produced.

In conclusion I can add that I am not sure when the PHU metric was renamed to thermal efficiency. There are many definitions of thermal efficiency so it is easily misunderstood. For rating fuel efficiency all solid residue is treated as a mechanical loss. Energy lost to unburned gases (also deducted for the heat transfer efficiency) is called a chemical loss. The heat in the ash is mechanical. Evaporated volatiles are chemial. Dropped fuel particles are mechanical. Raw fuel that is too small to be worth sending back to the supply is also a mechanical loss. In power stations they consider all these things very carefully. We can't just 'make stuff up' and declare that it has value and validity because we appropriate a popular term.

It would be most helpful if you could answer the questions I pose above because that is the best way to arrive an ‎accurate and broadly accepted answer to the char questions.

Regards
Crispin

Crispin,

Nice comment.

Your response passes the test about saying something truthful and useful.

It did not pass the test of addressing the question that I asked.  The question remains,
I would greatly appreciate some knowledgeable comments about how THOSE OTHER TESTS handle the issue of charcoal that is left in the stoves.   Is there some agreement between those many tests?
Maybe there is a problem with my question.   Or maybe nobody actually knows how remaining charcoal is treated in those tests.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu<mailto:psanders at ilstu.edu>
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com<http://www.drtlud.com>

On 1/22/2017 6:19 PM, Crispin Pemberton-Pigott wrote:
Dear Paul

There are two things to check. First, what is the question that is being answered? Second, does the metric provide the answer to that question.

‎Of course it is obvious that the question has to be valid in the first place and the method of determining the answer has to follow basic principles.

Something that is surely not well understood by the 'results-using public' is that all measurements have an uncertainty. All calculations involving measurements pass that uncertainty on. The result given in response to any question therefore has an uncertainty. When that uncertainty is larger than the supposed benefit there is doubt that the stove meets the standard of 'better'. When the uncertainty is much larger than the gain or loss, benefit claims are worthless. That is the point of Fabio's paper.

‎There is a study of indoor air quality in Ulaanbaatar gers (yurts) by a Korean team. They concluded that homes with improved stoves have 'significantly worse air quality' than homes with traditional stoves. 260 v.s. 210 microgrammes per cubic metre 24 hr average (in winter).

Gasp! Horror! Solid fuel improved stoves make the problem 'worse'!‎ Alert! Alert!

Let's look at the statistics. The uncertainty on the '201' number is ±187. On the 260 it is ±201.  The claimed difference is 50. The uncertainty is >3.5 times larger than the 'difference'. The claim for 'significance' is meaningless.

Next, what was the outdoor air quality during these measurements? All combustion and excess air has to enter the home from outside. ‎It was >300, higher than 260 the whole time. Oops.

They only proved that there is statistically no detectable difference between indoor and outdoor air quality whatever the stove type.

Cancel the alert.

So it is not enough to provide a test 'answer' it has to be accompanied by a range of uncertainty, or factored into it as I am suggesting for a 'warrantied rating'. ‎The uncertainty can be limited by very accurate instruments and a well-designed protocol and zero conceptual errors.

Regards
Crispin

To Crispin and all,

Crispin wrote about other tests of stoves (not the WBT water boiling test):

We should concentrate on evaluating others. There are several. EPTP, MWBT, CSI, BST, HTP, IS 15132 and so on and on. Let’s get on with it.

That is quite a list, including the "and so on and on."

I would greatly appreciate some knowledgeable comments about how THOSE OTHER TESTS handle the issue of charcoal that is left in the stoves.   Is there some agreement between those many tests?

And be sure that the discussion relates to the stoves that INTENTIONALLY DO LEAVE CHARCOAL BEHIND.

Some useful numbers (in general) relating to char-making stoves (specifically TLUDs), and based on dry weight of fuel and charcoal:

100% of fuel (wood) includes 100% of the carbon in the fuel

Charcoal (weight) yield is about 20% of the dry weight of the fuel.

Char (energy) contains about 30% of the ENERGY that was in the fuel (char is more energy-dense (by weight, not volume).

Char (carbon atoms)contains about 50% of the carbon atoms of the original fuel.

The big cause of those different percentages is that wood is a carbohydrate, which includes some oxygen and hydrogen atoms which influence the possible energy (release and burn the hydrogen) and influence the weight (Oxygen has weight but no energy value).

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu<mailto:psanders at ilstu.edu>
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com<http://www.drtlud.com>

On 1/22/2017 3:36 PM, Crispin Pemberton-Pigott wrote:

Dear Frank

I can add to the uncertainty, which I think has been pretty well covered in the journal articles, the issue of the validity of the reporting metrics themselves. This was addressed squarely in Zhang, Y et al 2014 which challenged the validity of all three IWA low power metrics

 .... snip.....

So I am dropping my call for a review of the WBT 4.2.3. Looking through the available literature, it has been done by several groups and all a new one will show is more details and defects.  We should concentrate on evaluating others. There are several. EPTP, MWBT, CSI, BST, HTP, IS 15132 and so on and on. Let’s get on with it.

Regards

Crispin

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