Post by matthewwalker on Jan 11, 2014 15:19:37 GMT -8
Well, I'm hoping to put together a video of this test I did last night, but I thought I'd post the data for you guys. As from the photos I posted last week, the heater does very well on CO once it gets hot and stabilizes. One thing that surprises me is how hot the stack still is, makes me think I might need to do another bench extension this summer. That's a good thing! In this one I cut the fuel pretty small, so when I load this run it overloads the stove for a couple minutes, O2 dives and CO goes way up. It recovers fairly quickly and does pretty well from there on out. This was a HOT batch. Too hot, hotter than I almost ever run the heater. It was good for low O2, but not representative of how I run it daily. It seems low 80% figures are pretty much the norm for the heaters I've tested so far. I assume that's pretty good real world performance, but I'm just starting so I'm not sure about that. Anyway, here's the data:
You can see the fuel light off and pyrolize there at 2 minutes, and O2 plummet. The heater takes 6 minutes or so to deal with that, and then is fairly stable. At 16 minutes the sticks burn away enough to drop altogether into the feed and again O2 drops, although it handles the fuel much better at this stage. If I hadn't used a charge with so much surface area I'm sure it won't spike the CO like that, although O2 would be higher. Fun stuff to play with.
hmm. 96% eff on Peter`s stove where looking impresive. I am wondering where this kind of the dofference is coming from. Do you have a trip wire and a P-channel in your stove? Also is it a one with the window?
trying to figure it out how to boost the efficiency. Although CO looks nice
Post by matthewwalker on Jan 11, 2014 15:46:49 GMT -8
No trip wire, no p-channel, window in front. I think this eff. number is pretty much on par with most of the data I've seen. 96%? I don't think I've seen a run that had that sort of average, although Michael's hydronic heater using Peter's core had some very good (93%) moments.
Post by matthewwalker on Jan 16, 2014 22:26:29 GMT -8
I finally got around to editing the video of the run, it's kinda boring, but perhaps some of you will get something out of it. I could certainly have better eff. numbers if I started with a cold stove, in this case the flue temp was 200°F before I even lit the stove. But, that's how I typically use it in the winter, the mass is always around that warm, so I think the test is a fairly accurate picture of an RMH in real world use. I think it's quite good, stable mid 80% efficiency for a very simple build. If anyone in the PNW wants to get together and test their heaters, I'm willing. I'd love to see how other heaters stack up.
Post by matthewwalker on Jan 17, 2014 0:44:03 GMT -8
Thanks Morticcio. I do actually have a friend with a BK "Princess" model. I was totally thinking the same thing, I'm really curious how they would test on the Testo. I'll see if I can convince him to let me test it.
Could you record your bench & ambient room temperatures for 8 or 12 hrs with the Testo? Would be interesting to see the changes the stove makes.
iButton temperature loggers are an option if you don't want to have the Testo running for too long. I have a couple of the which I use for recording outdoor temperatures at my house in Italy - they export to a .csv file so can graph with Excel afterwards. They only record -30°C to +70°C though so probably only suitable for room temps.
The efficiency value of a Testo does reflect the thermal efficiency not the combustion efficiency. The Testo efficiency value reflects the total amount of heat available from the fuel minus the losses from the gasses going up the stack. The efficiency value would only reflect the real thermal efficiency if the flue temperature is measured after the mass, where the remaining thermal energy leaves the house.
The measurement would have to be performed at the hottest point in the stove and the coolest before leaving the house. At the hotest point AFAIK the standard thermometer of a testo would be destroyed quite fast.
A rocket mass heater with low exhaust temperatures, as in the book, has a thermal efficiency above 90%.
The CO/CO2 Ratio (COR) A measure of how completely the fuel is being burned can be determined by dividing the CO by the CO2. Fully combusted carbon emerges as CO2, partially burned carbon as CO. The better the combustion, the lower the proportion of CO. This calculation can be made with any level of dilution, provided both are determined from readings taken at the same time. As the CO is usually given in ppm and the CO2 in %, a conversion factor is needed to determine their relative abundance.
COR = CO/CO2
Example Suppose the levels are 500 ppm CO, and 10% CO2 First convert the CO ppm to CO% 500ppm CO/10,000 = 0.05% CO
Then divide the CO by the CO2 COR = 0.05% CO/10% CO 2 = 0.005 = 0.5%
The target of a stove developer is to achieve a COR of 2% or less. Very low readings are possible in modern stoves.
BTW half of the thermal energy of carbon has been released in CO, thus a COR of 2% means that 99% of the thermal energy has been released. A COR of 0.5% as in the above example means 99,75% have been released.
The behaviour of your 8" RMH isn't any different as compared to my tiny 4" experiments during 2011. The larger stove is a bit more stable, not the same level of nervous jumps in CO and O2 but the spikes are still there. Probably more so after a cold start. The excess air could be lower resulting in higher efficiency, but the risk of CO spikes would be higher as well. I am very curiuous what you would get when using a simple p-channel plate.
Testing other stoves is a great way to learn how to interpret those figures, after some time you'll get the hang of it.
Post by matthewwalker on Jan 17, 2014 10:08:17 GMT -8
Thanks for the comments guys, I'm learning a lot as we go here.
One note on my numbers and something you said there Karl:
A rocket mass heater with low exhaust temperatures, as in the book, has a thermal efficiency above 90%.
This is something I've been thinking about since I started testing my heater, and I'm happy to have a chance to discuss this. Here's the thing, in order to have significantly lower exhaust temps I would need to start with cold mass. I have no doubt that if I started with the mass around 50°F I would be seeing much higher eff. numbers. However, in the real world of using this thing as my sole heat source, if I did that, I'd be frozen. So, I think this represents actual real world use of a heater like this. The mass is always warm, all winter. In my "living with the rocket mass heater video" I put thermometers on the mass for 12+ hours after a burn. The surface of the mass was >140°F, so internal temps and therefore stack temps are never much below 200°. That's the reality of how one of these is run in my opinion, so I wanted to show that.
Peter, the excess air is a challenge, isn't it? In this specific case, I am pretty sure I always run with quite a bit due to the fact that if I fuel the stove to capacity it is WAY TOO HOT! I almost never get the barrel glowing, and when the 8" is fueled to where the O2% drops much below 9% it is comparable to the batch burner stuffed to capacity. The barrel top exceeds 1000° easily and starts glowing. Too much, too fast, for my needs.
I will install a simple P channel and give it a run before too long here, I'm curious as well.
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deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
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deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
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deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
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dcoyte: I am planning to use a cast iron heat exchanger out of a hydronic boiler set on top of my rocket stove, flue out the top. There will be a pump moving the water through the heat exchanger into an unpressurized 2000 gal tank. Any thoughts?
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