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Post by patamos on Jan 9, 2014 8:37:49 GMT -8
Hi All,
I'm interested in anyone's opinion on whether widening the horizontal flue in 90 and 180 bends really matters in a well designed rocket system. Many years ago a grundofen builder/restorer from the Weimar told me to widen the turns so that the flow rate remains as constant as possible... ANd yet i've heard Earnie and Erica say that even 90 degree T cleanouts in the corners 'don't make a difference in flow'. Would it be more accurate to say 'don't make enough of a difference to bother modifying galvy tubes?
The old grundofens tended to have rectangular flues with lots of friction. Round flow way better....
A good rocket heat riser pushes harder than a bigger masonry heater fire box...
Is there anything i am missing here?
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Post by matthewwalker on Jan 9, 2014 9:50:45 GMT -8
I've got 8+ elbows in my 8" home heater, and it works beautifully. I'm inclined to disagree with the idea that elbows add 5' or whatever to the possible flue run length calcs. That said, using a small half barrel is a cheap way to make a plenum where flues change direction that offers a lot of design options. Personally, I wouldn't worry about widening elbows for possible draft issues, especially as this is a small system, but rather as function dictates. A larger plenum for turns can be designed to be a small bell to create warm zones at the typically cooler ends of a run.
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Post by patamos on Jan 9, 2014 16:11:53 GMT -8
Thanks Matthew, Well, after all my mental preparations and lengthy writing, i have arrived on site and found the walls have been framed up differently than anticiapted. I now have no more than 5' of bench space under a stair well for a mass bench before it butts intoa big post, and therefore no way to clean out the intended runs in the backrest. (The post in the right of the pic protrudes 6" form the lath wall to the right and 14 from the wall to the left. I had anticipated the whole wall being flush with the post.  So...Your split half barrel approach is now coming strongly to mind and i am wondering how far you got in experimenting with that, and conclusions you have drawn of late. If i recall correctly, you set the infeed port from the downdraft chamber close to but higher up than the exit to vertical. ANd this worked well(?) I can see how i would T- off the infeed port to create the double flue set up. It would occur about 18" behind the flue in the existing temporary set up. The flue would then dog leg forward higher up to go through the hole that has been cut through the ceiling. So long as i place cobb in layers with drying intervals and burlap or fiberglass mesh closer to the bench surface, i think i can build it air tight and strong enough to hold up over the longer term. Might there be any point in extending the infeed channel deeper into the bell area to enhance the heat dispersal? Also i will have 25+ft of vertical flue pulling from above the exhaust port, so i wonder if i may need to slow things down in the bell? .Maybe a smaller bell upstairs (if the ISA needs boosting), or a bit of horizontal routing there if the whole thing wants to pull too fast... Perhaps this should go into a thread titled 'indoor split barrel bell' But for now any feedback will be much appreciated. Attachments:
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Post by matthewwalker on Jan 9, 2014 22:03:43 GMT -8
Hmm, dang Pat, that's not much space. Lots of stuff to cover in your post, and I'm not sure I'm following your description (infeed?), but I'll answer what I can. Hopefully others will chime in here as well. Man, that is just one of the best tools in the kit, in my opinion. The original concept came from that outdoor bench/bell where I used sticks as lath to form the top. I viewed the half barrel as essentially a permanent form for the cob, to make a large hollow with a strong structure. It's really grown into a problem solver for me. I have no caveats with that system. Folks worry about sealing, but in a classic RMH there's a dang cob beehive for the transition area. In other words, and I don't need to tell you this, but cob is just wonderful at solving things that seemed like problems before your hands were dirty. Sealing is just a non issue. I think they are great solutions for areas where you don't need or want much mass, and they can be incorporated into high mass builds as well, but if you use 55g drums, there's quite a bit of space in there. So, in a small area, if you want high mass, it might not be the best solution. Conversely, you can configure them as bells and (perhaps) get relatively long heat cycles with lower mass, or at least, mass in a different shape. Other way around, put the bypass higher than the mass run. That way, things will start up easier, and then once warm you can use the draft to pull through the lower loop. I think it would only increase resistance if you have a true bell. On the other hand, you may have just come up with a new type of flue run. I'm picturing a single infeed flue running through the inside of a half barrel bench to the end of the run then the gasses returning inside the half barrels. Flue in a flue. Crazy, but it just might work. The downside to just the half barrels as a bell in a horizontal configuration that long is it is slow to heat the far ends of the dead end since things are rather slow moving in the bell, so that crazy idea just might solve that! Not only that, but you wouldn't have to have the exhaust exit lower than the infeed. Hmmmm. Tangent alert. Mind=Blown.  Unless there's some reason not to, on this build I'd be inclined to do a standard double 6" flue run out and back for the bench. I think you'd get a lot more mass in the small space than the half barrels would allow. Maybe a half barrel plenum at the far end to make the 180°, to maximize transfer surface area at that spot where you want it to bleed heat into the mass most. Since it's for someone else, I'd think you want to stick to tried and true, and not too tricky to run or maintain. I wouldn't worry too much about no clean outs in the first run to the wall, as long as you put some at the far end. I've got a 10' vacuum hose I can easily snake around a 90° for cleaning longer runs. As long as you have a cleanout at the barrel end of the run and the far end I think it could all be cleaned fairly easily. As for the upstairs addition, that can be tackled down the road if you feel like you are sending way too much heat out the chimney. That won't happen until you get the cob dried out on stage one, so just take it in steps. Way better to have a system that runs great in all conditions but maybe blows a bit of heat out the roof than to have one that's right on the edge and falls flat when conditions aren't right, in my opinion. I've added on after the fact on many systems, and, in fact, I'm learning that this is a good way to maximize your system. You'll have a much clearer picture of what it can do once it's up and running. |
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Post by matthewwalker on Jan 9, 2014 22:13:28 GMT -8
Just saw your cross post with me in the Half Barrel thread. I think a half barrel bench would work for you in this situation, and I agree that the tall primed chimney would allow you to stuff the exhaust down low for max heat in the bench. I said above no caveats, but that's not exactly true when using the half barrels as a true bell as you intend. It works great, but the gasses move slowly in the bell so that far dead end will be slow to heat. It will get hot there eventually, but much more slowly than using the barrels such that the gasses flow from one end to the other in transit, if that makes sense. I've made dead end half barrel benches, but I prefer to put the exhaust at the far end if possible, which negates your bypass, so I'm sticking with my recommendation above.
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Post by patamos on Jan 9, 2014 22:58:36 GMT -8
Thanks again for your advice Matthew. Deeply appreciated
I hear you about taking it one step at a time re upstairs modifications. Makes sense to err on the hot side heading up.
Clarification re bypass location. Planning to T it off the tube leading from down draft into first flue run. Aiming the T upward at 11o-clock to line up with primary and return flues heading towards ceiling. Will place damper in between where it makes sense as the body of the heater shapes up.
love the video
definitely a day of discoveries.
A input flue within the bell flue to the far end. Then let the gasses mingle their way back. Very interesting.
Thinking about how to sequence the build... maybe set the galvy pipe down on the ground in the belly and cobb it to completion. Then set barrels over top...
Definitely worth a go some time or another.
ONe issue coming to mind with the barrels is how to equalize the dispersal of heat through the cobb covering. Seems the crest of the arch is where i'd want the most insulation (say an inch of clay perlite) sandwiched in the cobb over... But this is also the weakest/thinnest cross section of the arch. I think the basic shape is a winner, and i have tremendous faith in the strength offered by a layer of burlap embedded 1/4" to 1/2' from the bench surface. Together they ought to be more than enough. Have your experiences shown you any trouble here?
Thinking now about a rectangular (L-shaped in plan view) bell made of cob and old bricks (of which i have many on hand). And creating a 36" CSA channel along the inner front face going from downdraft exit to far end of bell. It would involve buying a dozen or so 2'x2'x1.75" concrete pavers and building an internal column or two in the L-corner. Slower and pricier to build than the half barrel to be sure. But could be a good way to get the ISA closer to the 40sq.ft. range. Long vertical surface radiating into the room at leg level would be a plus. With the double flue bypass i'm sure i could prime out any cold slugs.
How do you think those pavers would hold up with the highish bell-top temps?
That said, I really like your idea of the bell at far end of the bench with flues coming and going. Totally makes sense to let the gasses linger there.
Presuming it would be wise to have the return flue exit lower down in the bell...
Looks like 6' of horizontal from downdraft chamber to bell with one 90 elbow. Then about 7.5' coming back (further back to the wall and under the stairs) with another elbow. How on earth to calculate ISA?!?!?
hybrid shenanigans...
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Post by pinhead on Jan 10, 2014 8:23:13 GMT -8
A input flue within the bell flue to the far end. Then let the gasses mingle their way back. Very interesting. Thinking about how to sequence the build... maybe set the galvy pipe down on the ground in the belly and cobb it to completion. Then set barrels over top... Definitely worth a go some time or another. I wouldn't cob over the flue within the bell. With such a short run heat dissipation "within" the bell wouldn't be wasted, as it will be fed into the mass anyway. One issue coming to mind with the barrels is how to equalize the dispersal of heat through the cobb covering. Seems the crest of the arch is where i'd want the most insulation (say an inch of clay perlite) sandwiched in the cobb over... But this is also the weakest/thinnest cross section of the arch. I think the basic shape is a winner, and i have tremendous faith in the strength offered by a layer of burlap embedded 1/4" to 1/2' from the bench surface. Together they ought to be more than enough. Have your experiences shown you any trouble here? I have about three inches of cob over the surface of my half-barrels. Once the bench is warm the heat is extremely even across the entire surface. also, I regularly stand, walk, and have even jumped on top of the barrel to test the structural integrity and am absolutely amazed of their resilience. Thinking now about a rectangular (L-shaped in plan view) bell made of cob and old bricks (of which i have many on hand). And creating a 36" CSA channel along the inner front face going from downdraft exit to far end of bell. It would involve buying a dozen or so 2'x2'x1.75" concrete pavers and building an internal column or two in the L-corner. Slower and pricier to build than the half barrel to be sure. But could be a good way to get the ISA closer to the 40sq.ft. range. Long vertical surface radiating into the room at leg level would be a plus. With the double flue bypass i'm sure i could prime out any cold slugs. How do you think those pavers would hold up with the highish bell-top temps? My 6-inch Peterberg stove puts out much more heat than the typical J-tube stove. The max temp I've seen on my bells (low-mass, mind you, which will produce higher temps) is 200°F. You'd be amazed how much heat is dissipated in the primary heat exchange (the barrel over the heat riser). That said, I really like your idea of the bell at far end of the bench with flues coming and going. Totally makes sense to let the gasses linger there. Presuming it would be wise to have the return flue exit lower down in the bell... Looks like 6' of horizontal from downdraft chamber to bell with one 90 elbow. Then about 7.5' coming back (further back to the wall and under the stairs) with another elbow. How on earth to calculate ISA?!?!? hybrid shenanigans... Bells are much more efficient both in terms of heat distribution and flow resistance than straight pipes. See my pic. You are right about wanting the flue exit low - close to/on the floor is optimal.  |
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Post by patamos on Jan 10, 2014 9:30:01 GMT -8
Very cool.
I am jazzed by all this evolution. Thanks for all the support you are offering here.
I am gravitating into building the side walls of the bell (bench body) with brick and cobb. Fire brick for the downdraft, morphing into old red brick along the front face of the bench. This way i can approach the final curved shape of the bench sooner than later.
The downdraft chamber off the side of the heat riser might start at 64" CSA (16"x4" or the like) and gradually shrink down to 36" once it curves and morphs into horizontal flue. Might be a 8"x4.5" chamber made of brick, maybe or 6" galvy pipe) just inside the front face of the bench towards the far end of it.
Kind of like a water fall dropping into a fast running stream dropping into a big eddy pool before accelerating again (up the exhaust flue) elsewhere.
Man, talk about natural building...
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Post by patamos on Jan 10, 2014 9:34:03 GMT -8
And talk about widening a flue turn...
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Post by matthewwalker on Jan 10, 2014 10:27:42 GMT -8
Ha, cool stuff guys! Pinhead, great thoughts and drawing, I love it.
I totally agree with Pinhead, don't sweat the thickness over the top. Half barrel is 11" or so high, so by the time you get to 18" bench height there's usually plenty of material over the top.
As for calculating ISA, man, I never do. When folks are talking about that they are typically discussing fairly involved masonry builds with large rectangular bells, and they need to get it right the first time. Not only that, but running more masonry heater style, start up from almost cold, store the heat in the bells, and shut it down. I think a typical RMH is run a bit differently, and with your bypass you'll have a lot of control over draft so I think you will be able to drive more mass, particularly as things progress from a cold mass to warm. You can run a whole lot more mass when it's all hanging out at 120° from the start, which my bench does all winter.
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Post by patamos on Jan 13, 2014 16:41:47 GMT -8
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Post by patamos on Jan 15, 2014 21:36:50 GMT -8
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