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Post by Orange on Oct 20, 2021 5:12:11 GMT -8
nice idea. Those stoves have a decent efficiency as they extract a lot of heat but combustion efficiency has to be like a regular box stove (70%).
those tiles can handle heat and if joints crack I just fill them with clay/sand mortar.
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Post by Orange on Oct 14, 2021 13:17:48 GMT -8
It seems that you have just one layer of brick on top of the bench. Am I right ?
You can add one or two layers on top (5 to 10cm). It will take more time to warm up but also to cool down (it stores more heat). Start with one layer and you will judge if you need it thicker.
you're right, one layer and I envisioned that it heats up quickly and that edges are warm etc. Like you said - thicker bench's disadvantage is more time to warm up and also increased height is not ergonomical.
I'm thinking of adding thin wood or metal grill so I can put matress on top so it doesn't start burning.
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Post by Orange on Oct 12, 2021 13:30:51 GMT -8
lighted full batch, after the middle of the burn CFB box seems to be glowing:
- CFB is rated at 1250C max, I've coated it with waterglass + clay - there is "burnt" smell, I really hope it goes away (not sure but think it comes from CFB as perlite and air-contrete are pretty inert and iron is uncoated) - bench gets too hot to sit on ranging from 80C to 150C, I have to burn less or increase ISA (I wouldn't like to increase bench height) - I've recalculated ISA an it's now around 5m2 (according to the specs it should be around 6,80 m2) - overal design seems great - enough power, most heat radiate low and towards the room, bench heats up quickly (magnetite brick are hotter than surrounding clay bricks)
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Post by Orange on Oct 12, 2021 13:13:55 GMT -8
satamax your method of fire startup is working well, there's no smoke comming back My thinking was to encourage draft in the early part of the burn, before the flue gasses have gone all the way through the heated bed / bench…so maybe a bypass damper would be the solution here? With the damper open, you could warm the chimney and get it to draw early — then close it once draft is established. ... You may already have good draft in the stovepipe and chimney, but if there’s a place where the system isn’t gas-tight anymore —even a small one— that could reduce the amount of draw exerted on the firebox unit at the front-end of the system, slowing down the pull of combustion gas into the heated bench/bed/bell. with bypass open (1/3 of CSA) chimney temp quickly goes to 150-200C. But even with those temps I feel like draft isn't good enough for the first part of the burn - that might be due to upper part of the chimney nor fully heated and small opening to the chimney that Satamax mentioned. Later in the burn with bypass closed chimney temp stays above 100C so there's no need to insulate or I'll be pumping heat out. Bench and firebox are airtight but metal bell isn't perfect as there are some metal on metal joints but there should be too much air leak.
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Post by Orange on Oct 8, 2021 6:31:58 GMT -8
tnx satamax , opening to chimney is 22x14cm=308cm2 (system size is 170mm diameter, so CSA is 227cm2). I will enlarge it if necessary but first I'll try your startup fire method. Forsythe - I have some insulation around firebox so back and right side of the metal bell don't get hot. I might insulate chimney pipe but what if chimney temperature becomes constant 200C - in that case I'm throwing heat out. I'll need to find balance.
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Post by Orange on Oct 4, 2021 10:22:43 GMT -8
fiedia closing bypass gradually helps!
stove runs well but for first like 15min door has to be open so there's enough air for the fire because chimney draw isn't established, and then some smoke comes out of front:
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Post by Orange on Sept 28, 2021 6:07:02 GMT -8
chimney is from bottom to top: 2m of thin galvanized pipe (170mm diameter), inside room, slight bend 2.5m refractory pipe(200mm diameter) inside hollow clay brick, inside room, no bends 1.5m refractory pipe(180mm diameter) inside hollow concrete, outside on the roof, no bends, with concrete cap on top
so it's not insulated but it's not terrible, worked flawlessly with basic metal stove.
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Post by Orange on Sept 28, 2021 0:43:54 GMT -8
Surprising, did you try to close your bypass gradually. The whole thing may need some time to warm up before closing totally.
Is it cooler inside your house than outside ? If the bench temp is at 20°C vs 24°C outside, it is impossible to get good draft.
- I didn't close it gradually since it's only 1/3 of sytem CSA.
- that's interesting, I guess it's a bit hotter outside
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Post by Orange on Sept 26, 2021 8:44:36 GMT -8
the thing still isn't working right - with bypass open chimney temps go to 150-200C but when I close it it quickly goes down to less than 50C and fire dies out. And it's still summer temperatures outside (24C). so the 2nd bell needs more destruction: In general, there seems to be two possible restriction points which are throwing up problems. The first being the transition from main bell to the bench. This should as wide as possible, meaning all the available space. As wide and high as the bench is internally. And the exit to the chimney should be low in the bench and at least 150% of the system's cross section area, preferably more. I'm suprised how other stoves (for example Vortex) work when gasses flow trough small tunnels, bends and lots of mass. In my bench many bricks are hollow to it's not that much mass. Also firebox is low mass.
original plan was to force gasses to the front of the bench where heat is needed the most but with the bad draw this wall will be destroyed: gass path from 1st bell trough 2nd bell:
this is situation after more dectruction, hopefully I won't have to enlarge that exit to chimney, we'll see:
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Post by Orange on Sept 19, 2021 6:02:19 GMT -8
It looks like a small fire in a large firebox, which most designs don't cope with well. Without the secondary combustion it cant burn clean, and without a fire big enough and hot enough to heat the firebox up properly it wont burn off any soot from startup on the ceiling. Only thing I can see in the mass that maybe could cause a problem is all those vertical ridges down the sides, that would increase the surface area but also create drag. Hope you can get it running right. yep, removing that wall inside bell and lightning bigger fire helped! - primary air frame: I used 50mmx50mm square tubes for the frame (30x44 openings). For your 170mm design, I understood that you use 60x40 tubes. May be you do not allow enough primary air inside your firebox. For my next design (200mm riser) I scaled it to 80x50. - coating: I just put oil the frame and it protects quite well against corrosion but not against water coming from condensates. The top window and its frame are a cold source. I get condensation there, inside the stove when smoke temp is too low. Water is then dripping along the steel and corroding the whole inner side of the frame. - air frame: yes, I didn't want a huge frame so I put smaller 60x40x3mm tubes. CSA-wise air should be ok, there's only one small restriction like 1cm from bottom air inlets. And doors are not airtight, intrerestingly heater can run with all doors closed - coating: I'm considering your option or coat it with waterglass. Or maybe leave bare metal. Hope you get your heater running right. Orange, insulate that chimney. That would be the first step i would take on a lazy burner. And, check and recheck for constrictions. I bet there is something you overlooked, which is restricting your draft. - yea without that bell wall I'm getting easy over 100C in a chimney. Might still insulate that spiral ventilation pipes, I've heard they can break in case of chimney fire. -exit port is enlarged, it's now greater than system size CSA. But wasn't enough I had to demolish wall in the bell too. The exit hole is to the side instead of the top front and there's no sign of a stumbler's block either. The foor channel's stub seems to strangely pointing to the side instead of to the port itself. And I am unable to see whether or not the riser stub is according to specs. You got an eye for details - floor channel is according to specs, I'm just missing a piece of iron on top of the riser stub
- removing that wall inside the 2nd bell helped a lot - I've got the stumbler so the only difference is exit to the side (like on batchblock), here's the current situation:
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Post by Orange on Sept 19, 2021 4:32:57 GMT -8
thanks guys, I've removed the wall in the second bell that was a restriction and it added to ISA: red part was removed:
so now it looks like this:
seems to be working well. Even got some nice discoloration:
as outside temps were still like in Summer (20C+) I'll need to test it when it gets cold.
only issue now is some bad smell above the first bell when fully heated - my suspects are CFB, old cast iron coating or air-concrete insulation (multipor) around the firebox. I think by the smell it can be air-concrete.
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Post by Orange on Sept 14, 2021 3:27:57 GMT -8
here's how it runs with bypass fully open (bypas opening is 1/3 system size CSA): chimney is this 2m metal pipe + 4m refractory pipe uninsulated. It worked flawlessly with the basic metal stove and ISA isn't huge so I expected no problems.
so yeah I'm thinking about increasing air velocity by removing restriction in the bell or insulating chimney (or both).
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Post by Orange on Sept 12, 2021 10:45:41 GMT -8
here's the whole thing. Doesn't run well, details below: inside the bench where gasses exit 1st metal bell. On the left are magnetite bricks for faster and longer heat transfer, 1 layer of standard bricks above for faster bench heating:
bench tunnel to the chimney. Hollow bricks + rockwool are facing wall to avoid heat transfer. Floor is from air concrete + clay (and OSB+EPS below):
mill scale grinded. Not sure about which coating to put:
top view 1st bell - minimalistic lightweight core (30mm firebricks):
CFB riser and top box. Exit port on the side to reduce stove height:
front view:
had to wear a mask while cutting CFB like it's a virus. It's coated with waterglass + clay mix:
doesn't run well, smoke comming from front:
went with backup plan - fully enlarged exit port (like on batchblock). Now it works better, doesn't smoke back like before. But I don't think it's burning clean because of dirty firebox and max chimney temp 120C with bypass (1/3 system size) open!!
I loaded only 1/3 of batch but didn't expect such weak results:
you can see the black firebox:
additional details:
- BB dimensions and ISA are pretty much according to specs
- chimney is not insulated but worked flawlessly with the basic metal stove - fire burns better with door opened than closed (I guess that's expected with more air)
- smoke sill comes from the front door even with enlarged exit port when bypass is closed (and chimney temp goes below 50C)
- upper window is useless, there are no flames and window gets dirty but I haven't burned full batch yet - bench is not heating properly, I might remove wall in the middle to help with gas velocity and draw
suggestions welcome before I demolish part of the bell.
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Post by Orange on Sept 12, 2021 10:10:05 GMT -8
yea if you don't have a lot of free time my advice is buy a tested finished product because here you have to account also finding and acquiring materials, drawing, planning, building, testing, debugging etc.
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Post by Orange on Sept 11, 2021 13:31:24 GMT -8
nice upgrades! Unfortunately the flames don't shoot out of the riser for more spectacurlar view.
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