[Stoves] FW: REQUEST for complete sets of raw data ofcookstove tests.
Kevin
kchisholm at ca.inter.net
Tue Apr 23 23:24:58 CDT 2013
Dear Ron
Please see my comments inserted below, starting with #
----- Original Message -----
From: rongretlarson at comcast.net
To: James Jetter
Cc: Discussion of biomass cooking stoves
Sent: Tuesday, April 23, 2013 9:27 PM
Subject: Re: [Stoves] FW: REQUEST for complete sets of raw data ofcookstove tests.
Jim: (cc "Stoves")
Thanks. A few comments inserted below
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From: "James Jetter" <Jetter.Jim at epa.gov>
To: rongretlarson at comcast.net, "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
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, lets call this E1. See also a later note about possibly needing to subtract energy in unconverted wood.]
# I would disagree with this approach, in that the 2 MJ of char energy is just as lost to the stove test, as is the 5 MJ loss.
If the char is “discarded,” then thermal efficiency can be calculated as: 3 / 10 = 0.3 [RWL3 E2]
# Whether the char is discarded or not is a situation outside of what happens within the stove system. The "Stove Test" should should report on stove performance, and should not be encumbered by factors outside the stove being tested.
The thermal efficiency for char production can be calculated as: 2 / 10 = 0.2 [RWL4: E3]
# I would suggest that this term is rather meaningless. If you could tell us how much energy was required to actually make char containing the 2 MJ of energy, and the theoretically required energy to make char, then one would have a valid term for "Thermal Efficiency for Char Production. The 2 MJ is simply the energy content of the char, and in no way reflects the energy required to make it. As defined above it is really "% of input energy unavailable for use because of char production".
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]
# As just noted, "Thermal Efficiency of Char Production" is a flawed concept.
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. 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.
# The "energy loss to char" can be given prominence in the test report. This will tell customers who do not want char how little it makes, and it will allow Promotional Char Makers to "fine tune their char making stove system" to maximize char production. "The Stove Test should test the Stove Device submitted for testing, and should report on what it found." It should be up to the Promotional Char-makers to add the "Yes buts...", like "Yes the overall stove efficiency is low, but look at all the char it makes."
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.
# That may be fine for Customers wanting char, but a "stove" is a device intended primarily for cooking and/or heating. Consider the case of a mal-functioning wood pellet stove intended for space heating. Assume its flaw was that it blew the charred pellets out of the combustion zone and into the ash pit. With your proposed Efficiency Rating, the ash pit carbon loss would be given full credit for having been burned, as it would have been burned in a properly functioning pellet stove. Your "Energy Efficiency Rating System" would cause great confusion.
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 degradation we have to emphasize this combination is possible]
# The purpose of a stove is Cooking and/or heating, not saving forests. However, "saving forests" is best done by using efficient wood burning stoves, or by designing stoves that burn "waste sourced" fuels. A well designed stove burning wood completely is inherently more efficient than one producing char.
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 with 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 example about E6=(3+0.5)/10=0.35]
I defend being able to combine apples (carbon neutrality) and oranges (carbon negativity) because they are at least equally important (I am leaning towards oranges).
# If the remaining char is going to be burned, rather than have to go to the trouble of having to "re-burn" it, why not simply purchase a stove that that burns it efficiently the first time through?? Your objection about putting the char back into the same stove from which it was made is a serious one... this implies that the customer would have to buy a second stove to burn the salvaged char. At any rate, each stove should "rise or fall on its own merits". Where the char was burned in the stove that made it, the same procedure could be used, and the results reported as a second test, because it used a different fuel.
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")
# Jim: If the stove test is to rate the particular stove for its "energy utilizing efficiency", then the energy in the char is "energy lost from the stove", and "energy unavailable for cooking/heating". In a Boiler Efficiency Test, "ash pit carbon loss" is treated as an energy loss from the test... what is the rational to justify not counting the char production as a "stove Loss"?
- 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 want this called "discarded". How about "cookpot-only"?]
# If the char is not used as a fuel, the it is discarded from, wasted, unused by the stove, etc. "Cookpot Only" could be construed as "misleading advertising", in that it does not warn the Customer he will have to dispose of unused char.
# Note that if the char produced by such a stove is used as biochar, having no fuel value, it is inappropriate to credit it with a fuel value in stove Efficiency tests.
- 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.
# As noted above the concept of "Thermal Efficiency for Char Production" is faulted. Any expression containing this term will be faulted also.
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 would suggest that this is a case of "the Tail wagging the Dog." The common conception of "Stove Fuel Efficiency" by Stove Customers and users is:
"For every 100 units of energy I put into a stove, X% is used to provide a desired cooking and/or heating function." Why not employ a Stove testing Protocol that most customers and users can already understand? The "Char Making Stove Community" could adapt the "commonly understood" test results as required by the "Promotional Char Makers".
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.
# If it makes char, why not call it for what it is?
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.
# Agreed. If the Customer does not want the char, he should buy a stove that does not make it in the first place.
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 am in favour of any stove testing protocol which:
1: Is scientifically based
2: Clear in the meaning of various terms
3: Easily repeatable by different testing agencies in different locations, yielding virtually identical results
4: Gives the Customer the information that will enable him to pick the best stove for his needs.
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.]
# I feel it is fundamentally wrong to calculate the efficiency of a char making stove by giving an energy credit for the unburned char. I feel this very misleading, and that it gives a false impression of efficiency that does not exist. I also feel that the term "Thermal efficiency for Char Production" is a faulty concept. For Stove Customers want to produce char, it is not helpful to rate char production in energy terms, but it would be helpful to report the weight of char produced as a percentage of "Input Fuel Weight"
[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 .
# One could probably write a book on the features and benefits of every stove. However, it would be good if the Stove Efficiency Test Report cound focus on the efficiency of fuel usage.
Best wishes,
Kevin
Best regards,a
Jim
The same . Again thanks -- Ron
_____________
From: rongretlarson at comcast.net [mailto:rongretlarson at comcast.net]
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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