Dear Ron
Please see my comments inserted below, starting with #
----- Original Message -----
From: [email protected]
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" <[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, 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: [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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