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Post by Solomon on Jan 27, 2021 8:13:18 GMT -8
Here's the situation. I want to build an 8" system with an L shaped bench and I could do split barrel, but I'm having trouble making the air sealing work in my head with the split barrel.
Here is the configuration: L shape, side A on the left is 9 feet long, side B on the right is 10 feet long. The chimney is located about 3 feet from the end on side A.
I could place the combustion unit at the end of side A next to the chimney and use a serpentine pipe setup to go down to the end of side B and back. Or I could put it at the end of side B and use a split barrel setup, OR two parallel pipes to move the exhaust to the chimney.
I've done the math on the ISA, I'm in a pretty good place in any configuration, probably going to have fairly warm exhaust.
The idea I have right now is to sit the barrels on a floor of Hardie board and then use cob and or silicone to seal them. I can also weld them end to end, at least for structural strength.
Somebody please poke holes in my ideas. Am I worrying too much about air sealing (and condensation) in the split barrels?
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Post by josephcrawley on Jan 27, 2021 14:15:21 GMT -8
Hard to picture how 19 feet of bench is well within ISA.
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Post by pigbuttons on Jan 27, 2021 15:02:47 GMT -8
Parallel pipes are probably going to be problematic. Everyone I've read about that tried to use multiple paths, no matter how close to identical, one will draw and the other(s) won't. Path of least resistance will always win.
i've attempted to locate the formula for ISA and hove only found the rule of thumb stuff from early on in some of Peterberg's posts. Can you post a link? Thanks.
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Post by Solomon on Jan 27, 2021 17:08:37 GMT -8
Hard to picture how 19 feet of bench is well within ISA. Because 19 feet is the length of the wall, not the bench. There is the core on one end and the chimney is not all the way at the other end. The bend of the L further reduces internal surface area. I have a spreadsheet. Show me your math and I'll show you mine. |
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Post by Solomon on Jan 27, 2021 17:12:14 GMT -8
Parallel pipes are probably going to be problematic. Everyone I've read about that tried to use multiple paths, no matter how close to identical, one will draw and the other(s) won't. Path of least resistance will always win. i've attempted to locate the formula for ISA and hove only found the rule of thumb stuff from early on in some of Peterberg's posts. Can you post a link? Thanks. Mathematically, channels equalize headloss. Adding heat and whatnot probably does screwy things. ISA is internal surface area not including the floor. So I calculated surface area of barrels and pipes. |
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Post by josephcrawley on Jan 28, 2021 7:45:39 GMT -8
Hard to picture how 19 feet of bench is well within ISA. Because 19 feet is the length of the wall, not the bench. There is the core on one end and the chimney is not all the way at the other end. The bend of the L further reduces internal surface area. I have a spreadsheet. Show me your math and I'll show you mine. Sorry not trying to be negative but that is still a very long horizontal run. It will be pretty difficult to get the draft started at that length. |
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Post by Solomon on Jan 28, 2021 8:36:37 GMT -8
So you're saying 12 feet of split barrel is long for an 8" system, but 25 feet of 8" pipe with four 90 degree bends isn't?
What length would you suggest? How many half barrels can I use?
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Post by Solomon on Jan 28, 2021 10:22:01 GMT -8
You say it's too long, and I ask about that, and then you change your tune and say the flue needs to be next to the barrel so you can have a bypass. These are separate issues.
I hear you. I have a solution for that. Compressed air blowing up the chimney.
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Post by josephcrawley on Jan 28, 2021 12:14:10 GMT -8
Solomon,
My advice is based on my own experience with rocket stoves. I have rebuilt the one in my house 4 times over the years and made quite a few stoves for other people. There are pathways that I and others have gone down over the years that ended in suboptimal results. I give advice with the hope to save others from making the mistakes I have made.
And yes the long run and the placement of the chimney so that a bypass is possible are the same issue. Without draw the stove will smoke the house up and no one wants that to happen.
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Post by Solomon on Jan 28, 2021 12:17:03 GMT -8
Yes, and the length of the bench is what you were initially commenting on. Then you changed tact.
So is 19 feet not too long now that the issue is having a bypass?
Just trying to get solid consistent info. I'm doing to be spending a lot of hours building this thing. I'd like to get it figured out on the front end.
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Post by josephcrawley on Jan 28, 2021 12:54:47 GMT -8
Yes, and the length of the bench is what you were initially commenting on. Then you changed tact. So is 19 feet not too long now that the issue is having a bypass? Just trying to get solid consistent info. I'm doing to be spending a lot of hours building this thing. I'd like to get it figured out on the front end. My gut says that yes 19 feet is too long but of course the only way to find out is to try it and see. With the pipe you could set it up with no cob and see what happens. Build the core on some heavy duty casters and if needed roll it closer to the chimney! My other concern is that an 8 inch J will take a very very long time to heat up that much mass. |
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Post by Solomon on Jan 28, 2021 13:02:33 GMT -8
Okay, what about 12 feet which is much closer to what the bench is likely to be? Maybe a total of 4.5 split barrels.
I'm just trying to gauge what your rule of thumb is because the Wisners is 50' of pipe minus headloss for bends, and Berg's is 101 sf internal surface area which works out to about 5.9 whole barrels or two barrels for the heat riser and seven half barrel length bench (which would be about 20 feet).
Just give me a number.
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Post by pigbuttons on Jan 28, 2021 15:02:44 GMT -8
Just some random brain storming here so let's see if it is of any value. You'll still want some way to clean out the split barrel section just like you need cleanouts in the tube version. The barrels are definitely easier to clean so maybe just two, one in the corner and one near the chimney end. End of the small storm.
Small squall still to come. I'm not clear how you will implement the compressed air to initialize the draft, but I trust you are and I'm sure it'll work. But my thought is that you could build an inverted funnel at the bottom of the chimney port inside the tunnel. Then you could use the cleanout port, if large enough, to start a charcoal fire under the funnel to initiate the draft as well. I do this in my j-tube with two briquets just inside the burn tunnel and it works every time as long as there is even slight positive pressure in the house because of the temp differential with the outside. But make SURE, very SURE, that the range hood is not running when you do this or the fire will come out of the feed tube and take the hair off of the back of your hand, ( just speculating, really! No, reaLLY, I'd never try lighting the stove with the range hood running! ).
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Post by pigbuttons on Jan 28, 2021 15:12:36 GMT -8
One other quick tip I've learned. Since the riser is well above the upper lip of the feed tube it will always draw. And if you make sure that the exit of the barrel that sits over the riser is just slightly above the top lip of the feed tube it is hard to imagine the whole thing running backwards. (Except as noted above, when introducing a negative pressure environment artificially.)
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Post by josephcrawley on Jan 28, 2021 15:23:01 GMT -8
Maybe a different approach would be to think of how big in mass a storage battery you need. The rule of thumb for that is 100 kilos per hour of storage. I'm not sure what a cubic foot of cob weighs but I'm sure someone has figured this out.
Put those engineering skills to work and you will have your answer.
I honestly don't know how many feet of "push" you can put on the end of a J tube. After building that first J tube stove years ago I knew it was not for me since then I build a more "traditional" masonry heater based around brick bells.
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