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Post by satamax on Jul 2, 2014 11:05:17 GMT -8
any more experienced builders have some critical feedback? Well, i'd say, that starts to smell like the eternal project. Too complicated and will never be finished! JRL, how many rockets have you built? Keep it simple. Just chuck a plunger tube, held by rockwool in the chimney, at the proper height for the right CSA, build your firebox and heat riser with something like clay slip, insulate the whole lot, fit a metal plate in front, with the right cutout. Hold it temporarily with a few concrete blocks, and see what happens. Then if it doesn't function like you hoped for, change things one at a time, to get better heat exctraction. Or am i a completely crazy, doomsayer noob, with no experience nor common sense?
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jrl
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Posts: 101
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Post by jrl on Jul 3, 2014 6:48:25 GMT -8
any more experienced builders have some critical feedback? Well, i'd say, that starts to smell like the eternal project. Too complicated and will never be finished! JRL, how many rockets have you built? Keep it simple. Just chuck a plunger tube, held by rockwool in the chimney, at the proper height for the right CSA, build your firebox and heat riser with something like clay slip, insulate the whole lot, fit a metal plate in front, with the right cutout. Hold it temporarily with a few concrete blocks, and see what happens. Then if it doesn't function like you hoped for, change things one at a time, to get better heat exctraction. Or am i a completely crazy, doomsayer noob, with no experience nor common sense? First test of this bell system last night was a flop. The fire burned well, but it didn't rocket at all. All the combustion was occurring in the fire box and not in the riser. The damper was sealed off except for the plunger tube, but I don't think the seal was good enough. The front facing (an old glass fireplace cover) never got even warm, except in front of the firebox. My next test is to seal the system up better, mud the bricks, seal off the damper better, seal off the facing better with sheet metal as you suggested, and see if I get any better results. When the rocket, un-mortared, is just setting in the fireplace with the damper wide open above, it takes off like crazy, so I know the core is good. I think I've decided that I don't have the space within the fireplace to do traditional metal barrel setup (would be square not round in my case). It just won't fit a big enough vessel around the riser. This leaves me with using the fireplace as a bell as originally hypothesized. I've also been reviewing the masonry batch heater created by Vortex. I like the idea of the multiple mini-bells made out of firebrick at system size. It makes the fireplace a mass heater. If the bell design fails, maybe something like that would wood in this space. I don't know if it would have much rocket action in that setup, but as long as you're getting full combustion, heat is heat.
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Post by satamax on Jul 3, 2014 8:22:39 GMT -8
JRL, to get things going, buy some denatured alcohol. You chuck a glass or two in the heat riser, pile up very quickly some wood sticks in the firebox, another glass on top of thoses, and "throw" a match onto the wood, this should get the draft in the right direction. Carefull tho, never ever on a hot stove, even a smidge more than lukewarm can give you bad surprises.
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Post by satamax on Jul 5, 2014 13:13:21 GMT -8
So, any progress?
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jrl
Junior Member
Posts: 101
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Post by jrl on Jul 5, 2014 16:33:54 GMT -8
Yesterday was rainy and cool all day, so I spent the day mortaring the core in place with Firestop refractory cement. It was a calculated risk to mortar it, but proved rewarding. I bent the edges of piece of aluminum sheet metal and fit it to the fireplace opening. I also sealed the damper as best I could in a makeshift way around the plunger tube. I estimate the facing was some 85% airtight, the core was 100% airtight, and the plunger/damper was 90% airtight. Anyway, once I got the front of the firebox piled with bricks to close it off and form the 20% CSA bottom-side air intake, the thing took off running with a small load of scrap wood. The core and riser aren't insulated yet, but it rocketed like one angry beast.
As for the bell effect... It was clear after 30 minutes of burn that a massive amount of heat was inside the fireplace and stored up in the firebrick walls and red brick mantel. In this regard, I think I achieved the fast/hot burn and complete combustion of materials needed. But, very little heat was radiating out into the room. 3 hours after the burn (only one half-load burn), the aluminum sheet was still too hot to touch even momentarily and the brick work was still massively hot. The lower half of the sheet metal, down near the exit to the plunger tube, was not hot at all. So the gases stratified, but only effectively in the upper half of the bell. I think I need to send the plunger tube down a few inches further to just above the floor.
I still think this bell concept is the only thing that's going to work for this design, but it needs convection tubes, a blower, routing of gases, something to get the heat out of the chamber into the living room. Also, shiny aluminum probably wasn't the right choice to conduct heat. I think some rectangular steel tubing, some air tight welds, and maybe a blower fan are in order. I'm also toying the idea of adding a small downdraft radiator over the riser, but not sure the effect this will have on the system.
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Post by peterberg on Jul 5, 2014 23:16:11 GMT -8
First, the plunger tube isn't insulated inside the bell yet. This is really necessary in order to avoid heat loss through the chimney. Second, that aluminum plate is good in conducting heat when it's black at the inside and out. A way to get more heat into the living room is enlarging the area of the blinding plate. Corrugated steel would be ideal, though unsightly and might be difficult to seal off. Sealing the whole thing is very important, it's the fine line between working properly or not.
The distance of the plunger from the floor could be as little as 4", provided it's got space all around. When that isn't the case, 6" would be probably sufficient. And last, a bell doesn't sport gas channeling inside, or it won't act as a bell anymore.
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Post by satamax on Jul 5, 2014 23:39:36 GMT -8
I'm wondering if you could get more heat into the room by using a steel plate in front, with welded fins on the inside of the bell. You could have many of thoses, spaced 3cm appart at least, that would increase the ISA localy where the steel plate is. May be you could make theses 10cm deep, and the height of the fireplace's firebox. Ten of thoses, 60cm high would increase the ISA of 1.2m² (two faces!) And that would rigidify the front too.
One thing you could do too, buy a cheap thermometer with a transmiter, you know thoses to check house temps inside and outside, tho the prob is finding one which goes to 80 or 100C° and put that in your chimney near the top. Which would give you some informations about your exhaust temps.
Do you have an elbow at the bottom of the plunger? If yes, i would bring this nearly to the floor. May be the bottom 3cm above. But if that's six inches tube, highest point is still about 8 inches above the bell's floor, while if your plunger was straight, as Peter said, you could go down to 4 inches. Well, in my calcs, you could theoreticaly go down to 3.74cm, if gases had no friction with the floor, tube edges and themselves, because of the change of direction in the flow. So 4 inch is a conservative figure.
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Post by matthewwalker on Jul 6, 2014 7:45:03 GMT -8
JRL, the aluminum is almost as low as you can get on the emissivity scale. It is just flat out terrible for that application, change to steel and you'll notice a huge difference in heat to the room.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jul 6, 2014 9:18:39 GMT -8
JRL, the aluminum is almost as low as you can get on the emissivity scale. It is just flat out terrible for that application, change to steel and you'll notice a huge difference in heat to the room. Aluminum is just what I had laying around. The real facing will be steel. I hope it does make a big difference. I'm going to just build the facing and see how it does, leaving room for convection tubes if they are needed.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jul 7, 2014 14:23:44 GMT -8
Had the day off today... progress. All-steel frame and 22 ga panel.
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Post by satamax on Jul 7, 2014 20:29:03 GMT -8
Doesn't look bad! Did you fire it?
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jrl
Junior Member
Posts: 101
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Post by jrl on Jul 8, 2014 4:50:48 GMT -8
Doesn't look bad! Did you fire it? Haven't fired it yet. It's not air tight. It's mostly just tack welds holding it together and I ran out of materials. I still need to add a 3 inch lip along the backside of the frame to hold it snug in the fireplace opening with some insulation. It's looking like the door frame and door will go on niceley. The gap between the frame and the firebox is for the 1" insulation that will be wrapped around the firebox.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jul 14, 2014 14:41:34 GMT -8
Here we go, more progress. I've got it fitted for a test run, plus welded up a little better. Plunger tube is insulated, and everything is mostly air tight now. I still have some more work to get completely air tight, but should be good enough for testing.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jul 15, 2014 5:45:17 GMT -8
I test fired it last night. I had a little back drafting issue at first. I think it was because the whole house fan had been on for a while and the attic fan was also on due to the high temperatures. As soon as the windows were all open, the problem resolved itself. Anyway, what I saw was every little orifice and crack in the system where smoke can leak out. It is obvious to me now that the sytem will never be air tight. That's no issue I guess so long as I minimize the places where cooler air from the living space can enter the bell. As for results, the system performed largely the same as it did with aluminum facing. It did marginally better due to more air tightedness, insulated plunger tube, steel facing, etc. The upper half of the facing was quite hot for a long, long time. Also, it used what seemed like a very small amount of wood to produce a very large amount of heat capture in the masonry. The brick in the mantel was still warm to the touch this morning. So right now the system is 'effective' at producing a good amount of heat and storing a portion of it in the brick and masonry, and radiating a portion of it into the living space for a long time. But, I have no means of measuring if the system is 'efficient'. It seems like it is more efficient than just lighting up some logs in the fireplace with the damper open. Right now the system is very 'subtle', the type of thing you light up when you get home from work and after an hour, the room starts to warm and will stay warming for a while after the fire goes out, but open the front door for a minute and it will take a long time for the room to recover. In terms of design changes I can go one of two ways: 1. Work to store even more of the heat and move towards a masonry heater type design. 2. Add more radiation / convection into the room by means of convection tubes, blower, radiant paneling, etc. My gut feel is that while it's storing a good amount of heat in the little masonry I have, I'm sending a bunch of it up the chimney. Again, effective but not neccesarily as efficient as it could be. As for convection, I'm thinking about building a second steel facing the same shape/size and hanging it out 3 inches or so from the stove. Bascially turning the whole thing into a giant radiant panel heater. This would passively get air moving across the steel facing without having to deal with blowers and tubes. What do you think? If I added such a panel in front of the stove, should it be conductive or insulative?
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Post by DCish on Jul 15, 2014 7:22:33 GMT -8
Sounds like what you need is more surface area interfacing with the room. Ideas already floated might help (corrugated front; fins behind and in front of the steel face; channels that go behind the face at the bottom and emerge at the top) but it might take several things combined to make the difference you want. Perhaps a simple experiment would be to place a regular box fan facing the face plate during the burn and see how much heat can be harvested just by introducing forced air circulation.
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