Jim: (cc "Stoves") Thanks. A few comments inserted below
----- Original Message ----- From: "James Jetter" <[email protected]> To: [email protected], "Discussion of biomass cooking stoves" <[email protected]> Sent: Tuesday, April 23, 2013 12:37:53 PM Subject: RE: [Stoves] FW: REQUEST for complete sets of raw data of cookstove tests. Ron, It was great talking with you in Phnom Penh. [RWL1: Agreed. I think you and GACC are to be much commended for that Conference coming off well. If anyone from GACC can tell us if Ppts (especially yours) will be available, that would be helpful. Let’s discuss a hypothetical example. We start with a batch of biomass fuel that contains 10 MJ of (potentially available) energy. After burning the batch of fuel in a certain stove, 2 MJ remains in unburned char, 3 MJ went into the cooking process (pot), and 5 MJ was “lost.” Thermal efficiency is calculated per the WBT protocol as: 3 / (10 – 2) = 0.375 [RWL2: For later use, let s call this E1. See also a later note about possibly needing to subtract energy in un converted wood. ] If the char is “discarded,” then thermal efficiency can be calculated as: 3 / 10 = 0.3 [RWL3 E2] The thermal efficiency for char production can be calculated as: 2 / 10 = 0.2 [RWL4: E3] 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] 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 somet imes the question is asked - how much "fruit" do you have and in this example the answer is certainly E4 = 0.5. 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. In a good stove, we are apt to see E2= 3, E3= 4, and only 3 lost (lets label this Elost.) I want those promoting the E3= 4 in char energy to be proud of, and promote, the E2=3 in cookpot energy. Way too much char is now being produced with E2=0. Note I intentionally did not drop the E2 value as I increased E3. Some char-making stoves are claiming that is possible. So my (not-to-be-calculated) E4 would be 0.7. To stop forest degradat ion we have to emphasize this combination is possible ] Now let’s say the remaining char is burned in a charcoal stove with 50% efficiency, then 1 MJ goes into the cooking process and 1 MJ is “lost.” Then we could calculate a cooking process efficiency for the system (including the char-producing stove and char-burning stove): ( 3 + 1 ) / 10 = 0.4 [RWL7: I have no problem w ith this, which we can call E5. What I would object to is always trying to put the char back in the same stove where it was made. Or if that is somehow mandated, at least also do a "best" different char-using stove as well, for what we call E5. Call the char combustion in the same (non-optimum) stove combination E6. That is apt to be in your e xample about E6=(3+ 0.5)/10= 0 .35] I defend being able to combin e app les (carbon neutrality) and oranges (carbon negativity) because they are at least equally important (I am leaning towards oranges) . For char-producing stoves, we plan to report: - Thermal efficiency per the WBT (remaining char gets full credit as unused potentially available energy) [RWL8: I don't mind this (assuming this is E1). But I could not define what this efficiency means as it is not in the "standard" form of E2 and E3. In your terms, we have " bananas ". (I avoided the word "lemons") - Thermal efficiency for the “discarded” char scenario [RWL9: E2. Fine. It helps to compare with and note there is an E3. For sure, the char-producing stove people will not wan t this called "discarded". How about "cookpot -only"? ] - Thermal efficiency for char production [RWL10: This (E3) is fine, and all I am asking for. It is already the subtracted portion of the denominator in the E1 computation, so no new work is required. No need to compute an E4 = E2+E3, - but I don't see how you can prevent people from thinking it . What we want to be sure to warn against is combining E1 and E3. I don't see any value in your carrying out experiments to determine an E5 and/or E6 - which is what I perceive Crispin to be proposing. Anyone wanting such numbers can put them together readily from your data from char-using stoves. If you decide to do testing to find an E5 and/or E6, I'd like another chance to discuss this further - especially if any testing can't acknowledge some users will want their stove to make char to sell or put in the ground (and not to burn) . I have no problem with you (anyone) testing a char-making stove to consume all the char. I would just not then call it a char-making stove. You will get really awful results if you try to stop any test part way and weigh an intermediate amount of char with most (any?) char-making stoves. You and Crispin are now in some disagreement I think - as I believe he wants to have other data than you have mentioned in this note. I haven't thought this all the way through, but I don't think much new will come out of hs proposed new testing - in a comparative sense. There might be some theoretcal value I have yet to see, but the amount of testing work seems excessive, with no benefit to users that I can see . As above, I hope we can have further discussion on adding anything along the lines of his last memo, if the testing involves something new relative to the handling and reporting of char production. I think reporting these results will provide complete information, and how others value the different efficiencies will depend on objectives (saving fuel, producing char, or a combination of both). [RWL11: Agreed. In sum, we appear to be in complete agreement (because I am not now asking for E4 numbers to appear anywhere, and I never wanted E5 and E6.] [RWL12: Both Crispin and I have perhaps recently raised another issue about subtracting unburned wood energy similarly to subtracting the char energy in the denominator of an E1 computation. It needs consideration in the Elost area - as that wood energy is certainly not lost in char-making stoves. But that is a topic for a different discussion .] [RWL 13: I have sometimes also mentioned that I would like to see a reporting in carbon or carbon dioxide (kg) terms as well as energy (MJ) terms. I believe the answers look a little better then for char-making stoves. But I don't think this requires additional testing on your part, so we can ignore for now. Aside: the "carbon apples" and "carbon oranges" look more alike than their joule equivalents . Best regards,a Jim The same . Again thanks -- Ron _____________ From: [email protected] [mailto:[email protected]] Sent: Monday, April 22, 2013 2:57 PM To: Discussion of biomass cooking stoves; Jetter, James Subject: Re: [Stoves] FW: REQUEST for complete sets of raw data of cookstove tests. Jim and stove list: 1. I like all parts of your message below, but want to comment on this sentence: " Meanwhile, we (EPA) will report future results per the current WBT protocol (energy in remaining char gets full credit in energy calculations), and we will also report results for the discarded-char scenario (energy in remaining char gets no credit)." I cannot concur that the "energy in remaining char" is currently getting "full credit" (as you and I discussed in Phnom Penh). An efficiency number emerges when the energy in the char is subtracted in the denominator - but a much larger efficency number emerges when the simple ratio of char energy over input energy is added to the cookpot energy over input. I ask that the separate char/input and pot/input energy numbers be added to the WBT data output. I also hope someone can explain what the present efficiency computation actually means - as it is so different from the simple sum of the carbon neutral and carbon negative stove efficiencies 2. I also feel that the testing for air-controlled batch stoves needs be different from those only controlling fuel supply. I am appending here a draft "memo" that follows one I found for charcoal-using stoves. I think this (39 kB) fits within the attachment rules given to us recently by list-master Andrew Heggie, but if it fails, I will re-send through Erin. 3. I will also respond to another message today from Crispin that suggests all char produced should be later consumed. This may be helpful addtionally - but the results for char only being intended for placement in soil (as above in (1)) should still be highlighted (and is not now). Ron
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