Crispin. Cc list and Jim See inserts below. New readers need to know that ">" below indicates a message yesterday from Jim Jetter. I have added some for clarity on who is saying what.
On Apr 24, 2013, at 8:25 AM, "Crispin Pemberton-Pigott" <[email protected]> wrote: > Dear Ron > > I think you will have to look carefully at what I am trying to achieve > because I find your restatements of my analyses different from my > explanations. RWL2-1. Apologies, if done. I know I used your name once or twice below, and I'll check. > > Jim and I agree, as for Paul A and many others, that the performance rating > of a stove has to be for that product, not a programme in which other issues > are included. The reason for this segregation is that claims made for a stove > have to scientifically valid. Claims made for projects that include > additional considerations also have to valid. RWL2-2. So far agreed, and hope you don't think I was doing differently. If so, an example? > I have no problem with projects doing all sorts of complicated things like > having a chain of stoves that use by products of each other, with calculating > carbon emitted or not. RWL2-3. I do have a problem with that, if it is part of the test protocol, which is the only topic Jim and I were discussing. > But when it comes to dividing the portions of such projects into their > (valid) segments, the rating of what happens in each ‘box’ as Frank calls > them, must stand on its own. RWL2-4. Sorry. Not understanding "projects", "boxes", or "Frank". In my response to Jim, no words like these appear. > One of the items on my ‘to do’ list is to share a perspective on the use of > terms like fuel efficiency and energy efficiency and heat transfer > efficiency. These terms are different and cannot be mixed together. A lot of > the misdirection on stove performance and fuel consumption has its roots in > the difference between energy efficiency (how much was used to cook) and the > fuel consumption (where remaining fuel is tossed or goes to some other > purposes). RWL2-5. I agree all should be carefully used. But the key here is whether Jim's list of three items to report are OK. They look OK to me. > > >Thermal efficiency is calculated per the WBT protocol as: 3 / (10 – 2) = > >0.375 > [RWL2: For later use, lets call this E1. See also a later note about > possibly needing to subtract energy in unconverted wood.] > > That is the energy efficiency – the amount of energy that was liberated and > the % of it that got into the pot (usually measured incorrectly, but bear > with me). RWL2-6. I agree. The question is whether that formula gives a fair and complete story for char-making stoves. I think it doesn't. I looked for "incorrectly", but didn't find it. > > >If the char is “discarded,” then thermal efficiency can be calculated as: 3 > >/ 10 = 0.3 [RWL3 E2] > > That is the fuel efficiency because it describes the consumption of fuel, > some the energy was liberated, some was not. Conventionally, these are called > mechanical and chemical losses (solid v.s. gaseous losses). RWL2-7. Hmm. So your argument is with Jim on his terminology, I guess. I only gave this the name E2. Note later I took issue with the term "discarded". I am trying here to look out for the interests of those trying to maximize this "discarded" quantity.] So the issue is whether E2 can be called a type of thermal efficiency. I am not willing to say Jim is wrong, as it has the right units and is measuring a thermal transfer. I think we have a semantics issue. And I am not sure that "fuel" makes anything clearer when thinking about making char. This needs more discussion. I am still comfortable reporting this number, and I think you are also. Or not? > > >The thermal efficiency for char production can be calculated as: 2 / 10 = > >0.2 [RWL4: E3] > > That is not a ‘thermal efficiency’. An efficiency is a ratio. The char > produced is not a ratio save expressed as a mass of char per dry mass of > input fuel, or an energy contained (potentially) v.s. the energy contained > (potentially) in the raw fuel. Neither is an energy efficiency because in > both cases no energy is released and no work is done. It is just a way of > expressing the mass or energy contained within some fuels. RWL2-8. I think all the ideas in RWL2-7 apply here also. But I can't agree with the next to last sentence. Energy was certainly released. A higher valued product was produced from a lower valued product. Maybe even more highly valued if put in the ground than if later combusted. I addressed the issue of also reporting mass - but that is trivial, and something a stove tester is already reporting (presumably with acceptable accuracy). Was work done? My brief googling on the words "chemical energy" and "work" says "yes" - so I'll wait and see if you want to argue on that. Certainly a lot of effort is now going into making char. > > >I think you are proposing to add the thermal efficiencies for cooking and > >char production: ( 3 / 10 ) + ( 2 / 10 ) = 0.5 > [RWL5: Right - E4= E2+E3] > > This is not possible because the units are not compatible. Making char is not > an ‘energy efficiency’. It is the processing of a raw biomass into a > processed biomass with a different energy density per unit mass. RWL2-9. You have not convinced me (or Jim?) that the units are "not compatible". I was fighting back in both 2-7 and 2-8, so I'll leave this to see if Jim or anyone else jump in. I am not asking Jim to report this E4, but I sure expect char-making stove developers to either use E4 or imply it. I personally still believe E4 to be a useful number. It is everything left over after tabulating true losses. No way that any char by-product is a loss. Yes making char can be put in energy efficiency units/ terms. If not in joules, then what? Your last sentence is of course true, but immaterial in the present difference in nomenclature.] > > >I’m not in favor of doing this, because, while there is a common > >denominator, I think the numerators are like apples and oranges – cooking > >(useful) energy and fuel (stored) energy. > [RWL6: I agree they are apples and oranges. But sometimes the question > is asked - how much "fruit" do you have and in this example the answer is > certainly E4 = 0.5. > > They are like comparing two different things which is why they have different > units. The analogy breaks down at the ‘fruit’ question because they are not > both ‘fruit’. One is an energy transfer question and the other is a fuel > processing question. [RWL2-10. I still am happy on units. In climate discussions, carbon neutrality and carbon negativity are regularly combined.] > > As long as the number "E3=0.2" is given a little prominence, I don't care if > the number E4 = 0.5 is also given. I expect promotional char-makers will be > using both E3 and E4, of course. > > Understanding why they cannot be ‘added’ is very important to this > discussion. They are different. Char making is a reportable feature of a > stove, if you wish. Jim and I agree on how to report the difference between > fuel consumption and energy consumption. The % of char produced from the > available carbon (for instance) is a third metric. It is not part of ‘thermal > performance’, it is one of the variables used in the calculation of energy > efficiency. It cannot be added to something from which it has just been > subtracted. Clearing up the prevailing confusion (if any remains) is an > important step in getting test results of comparable value. [RWL2-11. Sorry. Still in disagreement. The issue for me now is whether it is appropriate for Jim to only report E1, E2, and E3. If he wants to change their labeling away from "thermal", that might be OK, but I'd like to see the change first. I didn't subtract E3 to get E2. Both are only measured quantities and given in proper easily understood units. I am not interested in E1 - as it undervalues (strongly) the value of the char, whenever char is a major part of the stove design - and even for Rockets and similar. The reason for this undervaluing is not clear - maybe has something to do with the energy in Hydrogen. I 'd enjoy further dialog on this big difference in the way char appears in the accounting. I am happy with what Jim is propsing to report. I still gather you are not. Much more important to me is the handling of the E5 and E6 testing - about which I possibly used your name incorrectly. Feel free to critique me further, but I don't know what I said wrong about your testing proposals. Do you concur that E5 and E6 testing is not needed for char-making stoves? Also, above you indicated you were in agreement with Jim on something, where I took it to mean that I wouldn't agree. Can you clarify if it goes beyond these three E1, E2, and E3 terms? I still have not commented on (nor closely reviewed) your long memo on stove testing. But it seemed to go way beyond anything above. I think the above is enough for Jim to accomplish. Ron > > Regards > Crispin > > _______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email address > [email protected] > > to UNSUBSCRIBE or Change your List Settings use the web page > http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org > > for more Biomass Cooking Stoves, News and Information see our web site: > http://stoves.bioenergylists.org/ >
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