[Stoves] Request for technology proposals - Clean Stove Initiative, Indonesia
Ronal W. Larson
rongretlarson at comcast.net
Sun Feb 23 18:19:41 CST 2014
Crispin (adding back in “Stoves”, the intended audience of our exchange)
This is to try to again get you to comment on what I thought was a major error in your presentation - and to which you only gave a “SNIP”.
1. About this particular SNIP, I said in my original (emphasis added):
"4. ……... The main point is at the bottom - non-physical results are being offered.” So obviously I have to come back to understanding anything that is non-physical.
2. This non-physical claim related to your last example, where you started it with the important word “simultaneously” (Presumably to show that char-making stoves had the chance I am claiming is not there. I am going to delete most of my remarks below in the interest of getting to the point. I keep all of yours, which I found to be correct. But you did not perform the energy balance, which I am saying is seriously wrong. To repeat, you have postulated a non-physical scenario. Again, this is to ask you to comment.
> I have encouraged everyone for several years to make this sort of calculation because if you have a char production target, say 18-20%, and you have a fuel efficiency target, there is a heat transfer efficiency target that will produce all the results simultaneously.
> I am confident that with the larger boilers, 20 litres, the heat transfer efficiency will be in the high 80’s. It is, after all, a gas flame burning in constant, perfect circumstances each time with no need for control.
> To calculate that, let’s use 85% HT eff and 3.5 MJ/10 litres:
> 1 kg fuel @ 17MJ/kg AR (As received) total 17 MJ
> 2 Stars needs 55% overall thermal efficiency (Heat in the fuel v.s. heat in the pot)
> 20 litres needs 7 MJ in the pot. 7/0.85 = 8.235 MJ of fire heat
> 2 Stars means using up to 7/.55 = 12.727 MJ of heat
> Difference is 4.49 <J or 155 g of char
> Mass of fuel used including making the char = 749 g with 155 g left as char (21%)
4. Then, having confirmed all the previous were correct computations, I added these computations to see how they fit in an energy balance sense - and they didn't
Eff1 = 85% = [7 MJ/8.235 MJ]
Eff2 = 4.49 MJ/8.235 MJ = 54.5% (This number is OK by itself, but not when 85% means an E1=Eff1 computation. You did not make this Eff2 computation or the next two either. Jim Jeffers certainly would.
Eff3 = 85%+ 54.5% = 139.5% - Clearly something wrong - the problem was just over-specified I think.
Eff4 = 7/(8.235 - 4.49) = 7/3+ - >>100%; not even worth calculating the GACC number. D (losses) would be negative.
>
> This is technically possible.
[RWL: and I say not, based on these calculations. But this can be salvaged, if by 85% you mean either Eff 3 or Eff4. Did you? Could you? I’d be glad to try recalculating everything if that was the case.
5. So this is to ask again what went wrong in your example re conservation of energy. I ask that you change something to fit with reality. I think you must agree that you were promising more than you could deliver for char-producing stove people? For others, below, you can see that Crispin is disavowing the Eff3 and Eff4 calculation option that I am still urging for Indonesia.
My guess is that your error is in saying that Eff1 will stay at 85%. Assuming the 15% loss stays fixed and we somehow get an eff2 of 54.5%, then Eff1 will drop well below the level 1 minimum value of 45% - showing a “failure” to not reach level 1 status - when in fact many would consider this a fantastic stove.
But maybe Crispin has another explanation.
6. One other thing to comment on is this exchange from below at my #3:
> 3. I don’t see in your computations that the input fuel weight has to change as you go from no char to char-making.
>
> Correct. I have assumed the worked examples provided that the input fuel was constant as it went from fuel burning to char-yielding.
The point is that you just can’t keep both the 85% efficiency (as Crispin calculates it) and new char. Char-making stoves of course are going to use more input fuel at the stove just to do the cooking task, but the stove suers leave much more standing where the (maybe illegal) char is made in the bush. If the char ends up as biochar in the field, this stove production is one of the best approaches - and may have only used ag residues.
7. I also saw a statistic that 40% of logging in Indonesia is illegal in Indonesia (http://www.illegal-logging.info/sites/default/files/uploads/CHillegalloggingreportcardindonesia.pdf ). This makes me question Crispin’s remark below that the Indonesian government believes: "At present all the fuel consumed is considered ‘sustainable’
Ron
On Feb 23, 2014, at 1:13 PM, Crispin Pembert-Pigott <crispinpigott at outlook.com> wrote:
> Dear Ron
>
> >
> 1. Sorry, but I am not happy with the response. Let me repeat what I asked:
> I think TLUD companies might find it interesting to enter on the water-boiling side of this RFTP. But it is not clear how charcoal will be counted.
>
> I think I have responded with respect to how the charcoal will be calculated.
>
> All along you have been interested in the energy content of the charcoal and the use of energy as a fraction of what is the total energy available in the fuel that is consumed.
>
> I have no problem with energy accounting – it is very helpful when designing a stove and when looking at the entire energy flow from ‘field’ to the ultimate release of all energy in the form of heat.
>
> The core issue is whether or not to report the energy consumed, of the fuel consumed. It is your preference, for reasons you have mentioned but perhaps not clearly demonstrated by calculation, to concentrate on the energy used when completing a task, rather than the fuel drawn from the source each time a task repeated. There is no need for me to repeat the calculation of the difference.
>
> The customer, in this case the Government of Indonesia, wants to know how much fuel is consumed (passes from the environment into the stove product) each time it is used. They have not asked how much energy was extracted from the fuel that is taken from the environment, they want to know the mass of fuel taken because the environment only has so much total fuel mass. At present all the fuel consumed is considered ‘sustainable’. They intend to keep it that way.
>
> We are all aware there have been problems associated with the manner in which fuel efficiency has been calculated using the WBT in its various forms. Basically, the idea that the heat transfer efficiency equals the fuel efficiency is a dead duck. Heat transfer efficiency is and always a proxy for fuel consumption but it is not a good one when it comes to comparing things programme implementers want to compare, which is “How long will this available resource last if I choose this stove over that one?”
>
> [RWL: I still can’t find the answer to my question. I think below you are answering my question saying that the energy efficiency equation to be used with the water heaters is the same as for the stoves efficiency computations. I think there is no counting of the char value in any of your efficiency computations.
>
> Then my explanation is clear. You have understood it correctly.
>
> >I think this is unfair and unwise.
>
> Well, take it up with the governments and programmes. There is no choice. You are in an advocacy situation, pleading for special consideration, or pleading for a different interpretation of what fuel efficiency means.
>
> I support you in your general quest to have the number present to be able to do complex programming involving, particularly, two stoves burning a single fuel in a chain, where the total energy used is not increased, but the total work done is.
>
> >If I am I correct in this interpretation of what you have written, then I recommend that those interested in char-making stoves stay away from this Indonesian opportunity.
>
> For what possible reason? Spite? It is a very good way to introduce TLUD technologies which are pretty easy to build and can burn very cleanly (though not always in spite of sweeping claims that they are, in principle). A TLUD does not have to make char. And a char making TLUD can still provide good service. There is in the pilot area, virtually no market for charcoal but that might change with time.
>
> Char-making stove folk will be universally unhappy with their reported efficiency results, is the only conclusion I can draw. I recommend they stick with the EPA/GACC approach instead. The following is to explain my reasoning.
>
> But the EPA/GACC approach includes the calculation of whether or not the char can be used in that same device and the final fuel efficiency determination will be exactly the same, save for any calculation errors which I believe have been eliminated with respect to this metric.
>
> [Reformatted] [My comments or the CSI-WBT interpretation]
> 2. Let’s start with a standard nomenclature (I have violated a bit maybe, due to lack of time. Apologies in advance for any typos.
> a. Energies (MJ) :
> A=energy into pot, [includes energy into the pot material]
> B= energy in input fuel (pellets, etc), [factored for moisture]
> C= energy in char, [bomb calorimeter if requested]
> D = non useful energy [not determined]
>
>
> b. Energy densities (MJ/kg)
> ED: EDb = 18 MJ/kg, [is the dry fuel value?]
> EDc = 30 MJ/kg (designed to give easy ratio of 5/3)
>
>
> c. Energy efficiencies(%)
> E1= A/B (this is apparently the Indonesian standard); [That is correct provided the understanding is conveyed as to the meaning of ‘fuel consumed’ and ‘energy into pot’ which are defined slightly differently between the GACC-WBT and the CSI-WBT]
>
> E2= C/B; [Is this the % of energy in the char over the dry fuel energy in the fuel consumed, or is it over the As Received energy in the moist fuel consumed? Important note: the result of these two calculations is not the same. The dry fuel energy potentially in moist fuel is higher than the energy available by burning it with that moisture included.]
>
> E3=E1+E2 = (A+C)/B; [This is novel and its purpose is not clear. It mixes some of the heat getting to the pot (excluding the pot material itself) and includes some of the energy in the fuel not burned. What are the units?]
>
> E4 = A/(B-C) (the present GACC form) [This is the form that was applied to the pre-GACC versions of the WBT and is now corrected to consider whether or not the fuel remaining (including the char) can be burned in the same stove. It has been quite difficult to hear clearly that you understand this. If you have any further confusion about it please correspond with Jim Jetter directly. A stove that cannot use the fuel remaining is not able to claim a fuel efficiency based on its heat transfer proxy. The reason is very clear: it gives highly misleading results as to who much fuel the stove consumes. A case in point, the Quad 2, was brought to this list for discussion more than 18 months ago and it was concluded that pretending the heat transfer proxy was equivalent to the fuel consumption was irregular. The above formula credits the Quad 2 with a fuel requirement of 636 g per 5-litre WBT, yet it consumes 1350 g (dry) per firing. The calculation gives a heat transfer efficiency (proxy) of 44% yet the overall thermal efficiency (per CSI-WBT and GACC-WBT as currently framed, gives 19%. The confusion was ended; credit for unburned char is no longer given if the product cannot burn the remaining fuel for the obvious reason that more fuel has to be obtained from the local supply in order to run the next burn cycle.]
>
> [snip]3. I don’t see in your computations that the input fuel weight has to change as you go from no char to char-making.
>
> Correct. I have assumed the worked examples provided that the input fuel was constant as it went from fuel burning to char-yielding.
>
> 4. I have scrubbed a bunch of computations here - and will start them again, after your response to the following. The main point is at the bottom - non-physical results are being offered.
>
> Please explain. The UCB and ETHOS WBT’s 3.1 and 4.1.2 respectively give non-physical claims for fuel consumption. IT was this problem which was addressed in the discussion about the Quad 2 stove because the claimed fuel consumption was less than 50% of the actual fuel consumption.
>
> Dear Ron
>
> I think there is an assumption which is not always true: that a TLUD makes char. It is true that stoves can be designed to produce char from the fuel placed in them – many types – but it is not the case that all TLUD’s have to make char.
> RWL: I did not make that assumption. I only want to know what happens during computations of repaired efficiency if the stove user wants char - for whatever reason.
>
> I am not sure what a ‘repaired efficiency’ is. An efficiency is a ratio. There are dozens of possible energy ratios available from a well-monitored stove test. If someone wants char, then the appropriate ratio would be the mass of available raw fuel, or the energy content of the available mass of raw fuel, and the mass of char produced, or the energy in that mass of char. One would be the % mass yield and the other would be the % energy yield.
>
> >>Where there is a fuel consumption metric based on the total fuel used per cycle, whether the stove makes char or not is up to the producer. A water boiler could have an heat transfer efficiency that was very high, make some char, and still meet the minimum 1-Star target of an overall thermal efficiency of 45%.
> {RWL: All true, but I am asking only for what energy efficiency equations are to be used.
>
> Those were given and correspond (loosely) to your equation A above, which did not include the energy absorbed by the pot material.
>
>
> The baseline device has an efficiency (based on raw fuel consumed) of about 17% which means it would take 1.3 kg of those same pellets to do the same thing.
>
> 1/3 x (65/17) = 1.3
> [RWL: Not sure why this assumption - 17% sounds low for TLUDs, even without counting the char value in the efficiency formula.
>
> The 17% figure was obtained from tests of baseline devices performing the required tasks. It is not an assumption, really, it is a measured value.
>
> We are down now by a factor of almost 4. Or maybe your baseline is for a rocket?
>
> The baseline stove is a Keren Stove in many cases – a locally product and very inexpensive clay stove much like a Mandeleo.
>
> [RWL: I assume from this sentence that the “overall thermal efficiency of 40%” is calculated by giving zero credit for the “unburned charcoal”.
>
> That is correct though it is a little more general: it does not give credit for unburned fuel that cannot be burned during a subsequent replication of the same burn cycle. Whether it is char or not is immaterial – if the test ends and there is unburned fuel remaining, that fuel is analysed as to whether or not it can be used in the next replication. The definition provided in the document is worded to reflect this so that the fuel consumption of all stoves is reported correctly and the reader understands how much new fuel will be needed to conduct each test.
>
> This is not fair to a manufacturer trying to make char, or a user hoping to compare stoves on a char-making basis.
>
> There is nothing which prevents such a comparison being made, and there is nothing inherent in the definition of fuel consumption that affects the result of such comparisons.
>
> [Snip]
>
> [RWL: Answering my question of what efficiency equation should be used, Jim Jetter would report eff4 =E4 = 8/(20-5) = 8/15 = 53%.
>
> This is only the case where 100% of the fuel remaining can be used in a subsequent replication. You seem to persist in not recognizing this. Please contact Jim directly in order to set your analysis straight.
>
> There is no difference in the efficiency calculation of fuel consumption save for the energy absorbed by the pot. The energy in the pot material is commonly used when making an efficiency calculation, for example the Indian test and the British test upon which it is based. The GACC-WBT is unusual in that it does not consider this as part of the energy transferred. Any time the duration of a test is short, or involves a large change in Delta T, the energy in the stove body and the pot material create significant changes to the rated efficiencies (heat transfer, overall etc). This is recognized in the UCB-WBT derivatives by conducting a cold and hot start which is one way to deal with the stove body thermal mass. The Chinese method uses a different approach but intends to capture the same information. It is therefore normal to consider the pot mass when making an efficiency calculation because that energy is available any time the temperature drops from the boiling point (which is does in common water boiling tests).
>
> How do we calculate the efficiency of charcoal making?
>
> You are free to propose a method. The CSI-WBT is not a test of char making.
>
> [Snip]
> Eff4= 53% I don’t see how this can be controversial; you just gave all three A, B, C numbers as facts
>
> It is not controversial. It is a (not very exact) proxy for the heat transfer efficiency. We want to know the fuel efficiency, that is a different goal and uses a different formula.
>
> >The point is that using your rule#1 for scoring, this stove fails to get 1 star.
>
> In the example I gave, a 1 Star rating is obtained for overall; thermal efficiency (45%) as a water heater.
>
> [Snip]
> [RWL: Of course, I do not consider either 40% or 25% as being the “overall thermal efficiency”. But even if your eff1 does go down, my eff.2 = 41.7% need not go up, if we are talking the same “T” stove as earlier. But assume it does, I see no reason to assume your “additional 138 g”.
>
> In that case I am not sure you followed the calculation.
>
> [Snip]
> The right way is to measure the char weight and use the proper energy content of that char.
>
> The right way of doing what? You want the mass of char produced somehow to reduce the rated fuel consumption value, is that correct?
>
> >>I am confident that with the larger boilers, 20 litres, the heat transfer efficiency will be in the high 80’s. It is, after all, a gas flame burning in constant, perfect circumstances each time with no need for control.
> [RWL: No disagreement. But we are talking a very large system to get these efficiencies - I would say much higher than 20 liters.
>
> I can get that using 1 litre in a shrouded pan on certain stoves.
>
> Do you have a citation for the 80% or (below) 85% with wood/pellet fuels?
>
> The highest I have seen for a non-dedicated (pot-using) cooking stove is 77%. With small modifications for optimisation and the removing of cooking functions it is easy to reach 80%. At low power ethanol and LPG stoves routinely exceed 85%.
>
> [Snip]
> This is technically possible.
> [RWL: and I say not, based on these calculations. But this can be salvaged, if by 85% you mean either Eff 3 or Eff4. Did you? Could you? I’d be glad to try recalculating everything if that was the case.
>
> It is possible to get 85% of the energy available in the fuel consumed into the pot.
>
> For reference: Baseline 17% eff = 1.211 kg fuel per 10 litres boiled
> [RWL: Exactly 20% of the 85% - factor of five improvement - while making char, but not using it in any efficiency calculation?
>
> You are going to have to keep up. The definition is energy in the pot divided by energy available in the fuel. It has not thing to do with making char. It is a system efficiency calculation.
>
> You were correct in your earlier comment that I proposed a 10% efficiency gift to the char makers but that was not accepted by the programme. Maybe next year, if there is judged to be a benefit from having the char, and people are willing to deal with handling it – something not yet proven.
> [RWL: didn’t make sense anyway - seemed like a number pulled out of the air, and I think that even more strongly now. I see no validity in the 45,55, and 65% values for the three water heating tiers.
>
> We did not consult you I guess.
>
> The numbers were discussed and agreed in committee. The proposed 10% gift to char makers was to introduce the concept that there may be economic value in the char – something you have held for a long time. I was helping you make that ‘sale’. So far there isn’t one. Once we have a viable system involving a value for char produced by cooking that does not turn the sustainable supply of fuel to an unsustainable one we can talk again.
>
> >>I hope this clarifies everything.
>
> [RWL: I think you can see I don’t think it has clarified anything.
>
> Then I cannot help you further. For those who have been able to follow the plot, feel free to recommend water heating devices and cooking stoves that meet the minimum performance criteria and submit them using the online forms.
>
> Thanks
> Crispin
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