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Post by matthewwalker on Dec 14, 2017 10:14:37 GMT -8
Hey friends, I've been wanting to have this discussion for a bit, and Yasin's new cook stove got me curious enough to take the first step. I'd like to talk about using our Testo results, how to compare them, what they mean about our heaters, what our goals are, what we think is good enough, etc. What sparked this is looking at results lately, and noticing the huge variance in efficiency numbers from Yasin's to Peter's to mine. Peter and I had our machines side by side and were able to verify that there is nearly a 10% difference in efficiency readings. Peter, you told me later you had some interaction with Testo and verified the differences in programmed eff. calculations for different regions. Well, I just called Testo myself to have that conversation, and sure enough, there are a few reasons why the variance. I was hoping for a correction or calculation we could do to compare our results, but it doesn't sound like it is possible. He verified that a Testo in France would give different results from one in the Netherlands, and one in the USA. So, what do you guys look for, what are your goals? I always chase the lower CO, since a low CO and a flat line to me indicate complete combustion and stable performance. I don't worry as much about excess air and efficiency, because my goals are ultimate cleanliness, not ultimate efficiency. I'm not even sure if I'm right that <100ppm CO@14%O2 is cleaner than 500ppmCo@9% O2, but I think it is. Peter, I know you chase excess air as a means to peak efficiency. You know I make the analogy that you are a drag racer. You are always trying to push to see how far we can go, and you run stoves hot and scary and are able to realize amazing efficiency due to your careful balance on the edge of control. Yasin, you seem to be the more balanced view as you are building real world examples for clients and need to reach many goals. What are your thoughts, everyone? Here's a recent run from my Tiny Cook Stove as an example. Eff. at around 87%, which is very high for my machine.
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Post by peterberg on Dec 15, 2017 1:48:45 GMT -8
Hi Matt, I think there's a way to compare our efficiency results in a more reliable way. By using the spreadsheet of Lopez Labs the calculation of the eff. is uniform at least. As an added bonus you'll also get the combustion efficiency, which is a good indication how clean a heater is burning. Yasin is already using this in his reports in the thread about his cook stove with a short riser. When we are using this method the results should be really comparable provided the diagram is starting and ending at the same point. Plus the fact that our analizers need to be calibrated once a year. Mine is and it seems that every other year the cells need to be justified and sometimes replaced, but I am not sure about yours. Yasin's is fine in that respect because that one is less than a year old.
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Post by Dan (Upstate NY, USA) on Dec 15, 2017 2:11:14 GMT -8
I was wondering the same things Matt was...
But I don't think Peter runs his stove "scary", hot yes, but scary to me means runaway which means excess air flow which is not what Peter is going for...
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Post by Deleted on Dec 15, 2017 3:47:40 GMT -8
Matthew thanks for that discussion, that's very interesting !
Is the 10% difference linked to the "lower heating value" ? What did the Testo guys said ? I know I have to add approximately 13% to north american numbers to compare them with european ones because of that LHV.
My testo is fine I compared it to a brand new testo and my results were a bit higher so that's good. I use Peter's protocol, the same scales and the same colors.
The only difference maybe is that I don't touch the air inlet because I don't wan't users to tweak the air inlet. In my opinion that leads to worst combustion in most of the cases. I searched for quite a while to make an air inlet that can only be fully open or closed.
CO-wise, my goal is not so much shear performance but stability and a short red coals phase.
- I search for stability because I've seen that there is a big difference between the way I use the heaters and the way the users use them. I've seen people who just don't believe top-down lighting, who don't want to use logs smaller than 10 cm in diameter, who don't have the mindset (it's not perjorative) to think about combustion, who don't want to check too much for the size of their logs and so on..
So I'd like to have a core that burns well in various situations, not only when used by experts. As of my knowledge the batch has been a very stable core. Plus now I hope to compensate possible mis-uses by an "inspection" glass on top of the riser and a bypass valve.
- I try to have a short red coal phase because if it is too long I believe the people will just not close the air inlet and the closing valve before going to bed or going to work, by fear of CO coming inside the house.
That's a real waste in my opinion. Even if they only close the main air inlet (which is quite air-tight in my heaters) there will be a lot of stored energy wasted because at the end of the fire the draft is very strong. So strong that there is hot air rising and cold air coming in from the top of the chimney flue. I say that because I measure a strong draft in the flue with the testo even when the air inlet is closed and because the same phenomenon happens with thermosyphoning systems. Just like when you turn upside down a bottle full of water with the cork opened. That draft is reduced when both the air inlet and the closing valve are closed.
Alex Chernov did some measures about that on a teplushka bell heater and he measured that in 1 hour the heater had lost 25% of the stored heat. The article is "determination of heat losses and efficiency of the heater using anemometer and thermocouple".
But then, above all, I search for sturdyness for the heaters. I like the set up I am testing now because the core plus the little bell above it can be built "free floating" inside the heater, just like contraflow systems. It's much more easy with that construction than with the standard batchrocket and its huge riser. In this way that core and the small bell will take the most intense heat but, as they are mechanically separated from the rest, the outer skin will be exposed to much less thermal stress.
In some previous heaters I have made compromises in order to make less heavy heaters, but now I'm not so proud of those choices (true single skin, no mecanical separation between the core and the rest of the masonry, no protection right above the exit of the riser). At one moment the users want to show off and make big fires in a row and then.. cracks ! Mainly from the top level of the riser to the top of the bell. And then I'm to leave my home to go and to drive 300 km to repair that heater.. not so funny !
Regards,
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Post by matthewwalker on Dec 15, 2017 7:58:36 GMT -8
Thanks for the dialog everyone.
Pin, "scary" is because in order to get low O2 numbers the stoves have to be absolutely roaring. It's not less air, it's more gas. You can raise O2 by closing primary air, contrary to what you would think prior to having a Testo. Peter runs so freaking close to the ragged edge it's terrifying, a good run is a lot of surface area of fuel gassing off at once in his heaters. It's amazing that they stay stable and keep CO constant without spiking when they are running so violently.
The downside I found is that by the second or third load, the coal and hot firebox offgas too much fuel at once, and you get overfuel and CO spikes. You can see this in Yasin's later run tests of his cook stove.
Peter advocates heaters well designed and built to have a single fire and heat the space effectively with that simple protocol. I agree with him, this is the ultimate situation. Wake up, build one fire, light it, close the door, walk away and forget about it until the evening fire.
In reality, my homes aren't built that well, and I usually want to cook, or have company that wants a fire, or I just want to sit by the fire all day. My goals are low CO in all phases, stable and controllable, able to be closed or opened for different burn rates, and able to be sequentially loaded without going dirty.
Due to these difference, I prioritize CO numbers over O2, and as long as I'm reasonable efficient and it's stable there, I'm happy.
As for comparisons of testing, Testo said that every country has a different set of calculations and that was the difference and why we could not compare. He stated that France had different calcs than the Netherlands, which are both different from the USA. Peter, my machine was just calibrated, I sent it in last month.
I am not good enough at math and spreadsheets to work the Condar calcs. Does it not require careful weighing of fuel and ashes and lots of other details?
I still am wondering about Co vs O2 regarding completeness of combustion. Does a low CO ppm mean complete combustion regardless of O2%? I know that O2 hurts efficiency because we are heating air that we then exhaust, but is higher CO and lower O2 more efficient but dirtier?
I ask because those of us with testos know that we can get the very best efficiency numbers when the stove is bellowing black smoke and cold. I'm trying to determine what figure you guys use as a guide that you are doing well, what your goals are with numbers, and what you are shooting for.
Peter, what are your goals, number-wise? What's clean enough, what is efficient enough for you?
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Post by Dan (Upstate NY, USA) on Dec 16, 2017 6:26:42 GMT -8
Higher efficiency on "Heat Extraction Cycle" yes.
But all the CO you send up the stack is wasted un-burnt fuel.
So high CO would be lower efficiency on the "Burn Cycle".
As to the question as what is better, its just like you say depends on your goals.
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Post by Dan (Upstate NY, USA) on Dec 16, 2017 6:32:34 GMT -8
The INTERESTING thing is that there are simpler and more efficient "yet to be made/designed/invented" stove designs that will result in better numbers for both.
You just need a Testo some materials and a desire to tinker.
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Post by matthewwalker on Dec 16, 2017 7:08:35 GMT -8
I find myself chasing cleanliness over efficiency, as long as eff is acceptable to me. As such I prioritize the ability for a core to run stable with low CO over low O2. I believe Peter's goals prioritize low O2 over low CO, in an effort to maximize efficiency.
My goals here are to establish some parameters to discuss these things. When we talk about a core being "clean" or "good enough", what do we mean?
Peter, what's good enough for you?
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Post by peterberg on Dec 16, 2017 8:58:19 GMT -8
<grin>I am having difficulties picturing myself as a drag racer, who's chasing efficiency and running heaters freaking close to the ragged edge. And yes, it's ragged, that's true.<grin off> Banter aside, in order to be able to stay safely away from that edge, one need to know where that edge is positioned. Only pushing to the limit could be of learning value in my opinion. And my idea of safe could differ from just anybody else's idea.
Matt, actually I want it all: low O² and low CO at the same time. Born from the times that I tried weird constructions and found out that both values could be dancing up and down together instead of low O² while CO is spiking up. Much later I found out there are also limits to this, fitting called the ragged edge. So from then on I tried to find out where the frontiers for different combustion cores really were.
So what is it that I am going for? I'd say 9 good runs out of 10 would be nice. A good run is one between 80 and 90% efficiency higher heating value, O² between 7% and 10% at the lowest point and CO below 500 ppm, all at the same time. Oh, and exhaust temperature around 80º C (175º F).
My own heater is tuned back slightly but is still quite close to aforementioned edge I would think. There's also another factor in play: I see fuel processing as plain work. Insulating the house aside, the higher the efficiency of the burn the less work to keep warm through the winter.
Having low CO numbers isn't enough in my opinion. Since CO is relative to the air moving through the system one should look at the undiluted figures but that isn't an encouraging way to do development. And as Wolf remarked, CO is fuel so the less the better. Years ago I dreamed about a combustion core which could run clean (CO below 500 ppm) while the excess air level being 3% or something ridicously like that. Lowest levels I've seen in just a handful of test runs was about 4% while the CO level stayed low, not repeatable at all. Thirty years ago stove builders did aim for 13% O² as the lowest pracical level, I would like to do about half of that as standard but I am not there yet.
And yes, my usage of heaters is very different from yours. And yours in turn is different from Adiel's or Yasin's or Max' so there ought to be different variations. Development of this core has been going on for only 5 years now, who knows what's in the pipeline in say, 10 years?
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Post by matthewwalker on Dec 16, 2017 10:21:59 GMT -8
What an awesome response, thank you Peter!
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Post by peterberg on Dec 17, 2017 1:20:45 GMT -8
I've seen people who just don't believe top-down lighting, who don't want to use logs smaller than 10 cm in diameter, who don't have the mindset (it's not perjorative) to think about combustion, who don't want to check too much for the size of their logs and so on.. Exactly the point why I don't like a complicated protocol. Chimney dampers, bypass valves, multiple air inlets and soforth tend to create a lot of room for interpretation. Even the cleverest of people who are operating the heater strictly according to instructions in the first year are getting sloppy in the second. Add to that the people who think they could "fine-tune" the thing without knowing anything about it while they have a vague idea of how the fire should look like. The smaller the instruction leaflet and the less complicated the heater construction, the less trouble during the lifetime of the heater. Although I have to add that a clear statement of "don't do this" isn't enough in some circumstances.
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Post by Deleted on Dec 18, 2017 7:39:02 GMT -8
I'm not even sure if I'm right that <100ppm CO@14%O2 is cleaner than 500ppmCo@9% O2, but I think it is. Matthew, There is a nice article here : www.hedon.info/docs/BP55-PembertonPigott.pdf about the combustion analysis. I find that the difference between CO and COundiluted is very well explained. Regards,
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Post by matthewwalker on Dec 18, 2017 8:35:41 GMT -8
That is a good article, thank you.
My Testo calculates CO Undiluted along with CO. If I remember correctly, Peter, yours does not? Yasin, does your testo show undiluted CO?
Maybe we should put that on our graphs?
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Post by peterberg on Dec 18, 2017 11:59:34 GMT -8
My analizer does calculate undiluted CO, it always has. In fact it's the CO multiplied by the lambda figure. We would need a radically different scale to put CO undiluted on our diagrams. It can be as low as zero or very close and in a spike it could easily be 30000 ppm. Readability wouldn't be any better like that. I tried it with a scale of 0 to 15000 which looks acceptable in a couple of diagrams.
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Post by Deleted on Dec 18, 2017 21:43:50 GMT -8
Matthew, the same goes for me. The scale is too large to show it but I always add it to the data I post here or on my website. I post the average values of the firing with CO undiluted being "COnd".
I find that undiluted CO below 1500-2000 ppm is an excellent average value for a whole firing. On the cookstove when it's in excellent shape the COnd is around 100-200 ppm during the best part of the firing.
The very best firing I have see was a straight batchrocket with a floor channel and insulating sleeves as the riser. COnd was around 50 ppm for 25 minutes. Impressive !
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