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Post by patamos on Dec 2, 2016 9:25:57 GMT -8
Hi Folks,
I've been intrigued for some time now byLars Helbro experiments with condensing downdraft flues.
I haven't seen testo numbers on the Gymse set up. But i understand that the 'push' from the pseudo-heat-riser is part of the process. So i wonder if anyone has tried coupling an optimized batch (or J?) with a extra long riser to the condensing exhaust system?
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Post by drooster on Dec 2, 2016 13:41:51 GMT -8
I looked at the MHA 2012 photo-writeup, but it looked like once the huge masonry stove was dry the descending flue did not work without additional and messy cooling by wet blankets ...
I don't know much but the insistence on a condensing descending flue seemed a bit silly, and in any case they refitted it to a normal vertical flue when humans arrived for a pizza gathering.
You did not include a link, so maybe I searched and found the 'wrong' writeup. Got a better link that justifies the condensing flue?
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Post by Vortex on Dec 2, 2016 14:53:15 GMT -8
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Post by patamos on Dec 2, 2016 21:28:24 GMT -8
They gave it another go two years later. Trying to create a more effective condenser. Info about that experiment is at this blog site: www.stenovne.dk/englishcentrifugalcarburator.html(scroll down to Aug 2014) Who knows if it will ever be dialled. But the possibility of claiming back the heat/energy otherwise lost to evaporating the water (that only wants to condense again as it cools…) seems to me a worthy pursuit. I'm just curious if others have played with it elsewhere...
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Post by ronyon on Dec 2, 2016 23:59:07 GMT -8
Neat! Seeing how they used wet fabric to cool the stack,could one run a stack through a water jacket?
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Post by ronyon on Dec 3, 2016 0:19:34 GMT -8
The blue barrel with the water sprayer and expanded clay spheres is more like a particulate filter. Notably, it includes a fan. The draft is destroyed by the cooling. So yeah, I too would like to see if the barrel/riser "pump" could over come this.
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Post by patamos on Dec 3, 2016 13:24:52 GMT -8
Ya i too am wondering about a water jacket.
Swapped emails with Lars. He figures the minimal vertical exhaust flue drop would be about 8 ft. But of course there is this delicate balance point of making sure the gasses are as cool as possible before starting the descent. Very tricky with a variable combustion rate and evolving harvesting temperatures. So the mechanical fan comes into play.
I'm going to play with it in my workshop, but also install a T junction upstream in the flue to be able to send the gasses up when necessary.
thanks for the jammin )
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Post by pyrolyse on Dec 6, 2016 14:02:18 GMT -8
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Post by patamos on Dec 6, 2016 21:49:14 GMT -8
Thanks Pyrolyse,
The video helps make clear some of the operating details and principles.
Interesting rocket core. Sacrificial steel riser? Pictures didn't show insulation around the riser but i'd assume there must be some. Otherwise looked like a low mass L-feed with a batch box in the front. Or was there a PVDB batch box port leading into the riser? And top air feed…. Like a J-feed batch box hybrid...
testo testo ??
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Post by Vortex on Dec 7, 2016 4:30:41 GMT -8
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Post by Vortex on Dec 9, 2016 9:43:54 GMT -8
Pat, After a bit of searching around I found the layout of the stove from this video: vimeo.com/158153306 The part on the stove starts at 5:15 It's in Danish but is visually quite easy to follow. There was already a thread on this forum from September where someone asked about the stove: donkey32.proboards.com/thread/2072/flex-furnace-flue-gas-scrubber And Peter replied: A Flexovn is the Danish interpretation of a Ianto Evans rocket mass heater. Ianto came to Danmark in 2001 to conduct a workshop at Friland and the guys over there adapted the design. The barrel went out and the whole of the heater was built out of brick. In essence, it's a J-tube with a glass door in the front and the air inlet at the top of the firebox. I'll second Karl in his opinion that a claim of 120% efficiency has to be considered a fairy tale. As far as I know nobody put this type of heater really to the test so whether combustion is complete remains to be seen.
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Post by patamos on Dec 10, 2016 9:09:33 GMT -8
Thanks for digging around Trev,
Ya the claim of 120% is over the top. They are likely getting all the benefit of energy released from phase change condensation within the dwelling. That is where the extra 20% comes from. Folks at the Central Rocky Mtn Permaculture Institute (CRMPI) have been growing tropical plants in winter via phase change heating in their greenhouses.
No doubt the Flexovn is also harvesting all the heat from combustion. So that saves another 5% to 10% that is usually sacrificed to drafting function
But the claim of 120% assumes optimized combustion. GIven all the work that Peter and Co. have put into trialling and testing Js and BBs, i'd be surprised if this set up without the port is faring as well as it could. Eg. what does the coaling phase look like?
Still, the overall idea is intriguing.
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Post by pyrolyse on Jan 13, 2017 5:24:41 GMT -8
Steen's condensing flue is interesting. The thing is though, it would seem he is not even near the temperatures or proper oxygen levels of Peter's batch box, because then that metal heat riser would deteriorate very quickly. I think Peter's batch box is superior in performance, but it would be cool to experiment with a condensing flue to rid the exhaust gasses of the last few particles. However, I don't think many people would want such a noisy fan in their living room, I don't understand why it is not placed somewhere outside. Steen is somewhat lacking in 'finess' and 'finish'.
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Post by patamos on Jul 14, 2019 17:56:40 GMT -8
Condensing flueas are once again in my mind, so thought i'd revive this thread. A quick google search brought up all kinds of examples at a macro scale. dallenergy.com/en_gb/biomass-technologies/flue-gas-condensation/I'm getting ready to build a heater for friends that has a steep drop off behind the house. So a purely gravity powered operation is in the cards... The build after that has only a 4' drop to surrounding ground level. BUt i wonder if a super efficient water jacket - more like a reverse boiler - could do the trick
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Post by gadget on Jul 14, 2019 20:21:56 GMT -8
Condensing flueas are once again in my mind, so thought i'd revive this thread. A quick google search brought up all kinds of examples at a macro scale. dallenergy.com/en_gb/biomass-technologies/flue-gas-condensation/I'm getting ready to build a heater for friends that has a steep drop off behind the house. So a purely gravity powered operation is in the cards... The build after that has only a 4' drop to surrounding ground level. BUt i wonder if a super efficient water jacket - more like a reverse boiler - could do the trick I don't think you can make it work without a blower fan. You would need to cool the gases way below outside temp. Say its 50F where your exhaust exits, you would need to have the flue down to say 10F as an example? I'm not sure of exact numbers but there has to be a decent temp difference. There is not enough push from the riser to over come everything in the system, you need the buoyancy difference at the exit. Maybe if you had a very simply system with no bells or mass restrictions but then how do you get all the heat extraction. As your temperature gradient decreases, your heat exchanger efficiency has to increase to make up for it. That typically means a much larger surface area and more restriction which kills flow. Blowers can be had for free and they take very little power to run. I have about a dozen of them that I get out of scrap furnaces. The last one I used to pull flue gases moved air very well through many restrictions and it only uses 80 watts on high speed. The other challenge is if you want to get 100% to condense, you will need a very large and efficient heat exchanger. I had lots of moisture condensing in my system and still there was lots of visible moisture out the exit. My flue temps would peak at about 90F after hours running at full power. Have you seen the thread I did on the forced induction mini rocket? I learned allot on a condensing flues with that build. If your interested in a water cooled heat exchanger I have a design for a copper one I am building but it would only work with a blower system.
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