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Post by craigmiller on Nov 12, 2014 19:07:43 GMT -8
I'm needing to know what to include in my ISA calculations. See the pictures of my 6" single bell up to this point here: Front ViewBack ViewSome explanation: The space under the batch box is to dry wood. The compartment above the batch box is going to be a white oven. I'm assuming all sides of the oven count toward the ISA. If I recall correctly, Peterberg says not to insulate the batch box. Do the sides of the batch box count towards the the 64 sq ft, or not?
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Post by peterberg on Nov 13, 2014 2:02:53 GMT -8
If I recall correctly, Peterberg says not to insulate the batch box. Do the sides of the batch box count towards the the 64 sq ft, or not? Yes, insulation of the firebox isn't necessary but the riser is. So for ISA, please take all surfaces into account. The outside of the firebox is different, though. When the heater is cold all the surfaces will absorb heat but when hot, the firebox is radiating heat. I would say, count the firebox as half. Oh, don't count any floor area.
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Post by craigmiller on Nov 13, 2014 18:56:35 GMT -8
Thanks peterberg! I'm going to use mesh to keep the ceramic fiber blanket in place around the heat riser. Should I use high temp mortar as a glue to help it stay in place?
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Post by hallinen on Jun 14, 2015 10:43:56 GMT -8
Hello Craigmiller, Thank you for posting picture of your batch box, very nice! I am curious as to how your 6 inch batch box is working out. Did the mesh work for holding the ceramic fiber blanket around the heat riser? What type of material and what shape did you make your heat riser? Are the bricks that make the bell firebrick? Do you have a glass door at the front of the batch box? Do you have any temperature data for your project? What was the exhaust pipe size?
Thank you, D
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Post by erikweaver on Jul 18, 2015 10:43:41 GMT -8
Most interesting. I wasn't counting the fire box surface area at all in my sketches so far.
Last winter (2014-15) I ran a 6-inch j-style, approx. 1-1/2 barrel system. This was to test the indoor operation and how I liked it. I liked the heat, but not the constant attention. So I'm now planning to switch to the batch box design, which I believe better fits my lifestyle. I am planning to have the batch box replace the j-style feed (the new heater will be entirely rebuilt, in a new location several feet distant from where I ran the j-style this past winter).
My plan is to build the batch box, and situate the approx. 1-1/2 barrels on top of that, so that the fire riser empties into the barrels, and flows out the rear-bottom of the stacked barrels, into a bell. Then from the bell, into the chimney.
So my ISA calculations would include the portion of the batch box that is within the perimeter of the barrels, the interior sides of the stacked barrels, and the exterior surface area of the fire riser?
(I am undecided upon fire riser construction at this point. I'm most strongly considering a fire brick riser, surrounded by rock wool; or re-using the clay-perlite mix I used in the present j-style riser, but this time making both the interior and exterior shells out of metal tubing (6-in. interior, 12-in. exterior dia. fire riser), and adding refractory cement to the mix in the ratio of 14:14:1, as per another thread on this forum.)
My understanding is for a 6-inch batch box, comprised of two bells, I ought to be targeting about 43 square feet of ISA. The interior of a single barrel is about 23 sq.ft., so an estimate of a 1.5 barrel stack would be about 34.5 sq.ft.
If the fire riser is 44-inches tall and 12-inch dia. it's surface area is 2*pi*r*h = 2*3.14159*6*44 = 1658.75952 sq.in. / 144 = 11.519163333 =~ 11.5 sq.feet.
So my estimated ISA of the 1.5 barrel/fire riser assembly is 34.5 + 11.5 = 46 sq.ft.
That is already in excess of the 43 sq.ft. target for the heater, so I have no remaining ISA for my bell; nor have I added the half-value of the portion of the fire box enclosed by the barrels. Yet I know folks have been making bells, so where is my thinking going wrong? I'm obviously missing something.
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Post by peterberg on Jul 18, 2015 13:01:34 GMT -8
The target for a 6" batch box up until recently has been 6 m2 or 64.6 sq ft. New experiences and calculations led to the conclusion this might be too much in a number of circumstances. So at this moment I think the maximum safe ISA of just one bell would be 5.5 m2 or 59.2 sq ft.
For the calculation, don't count the floors of the bells and don't count the enclosed suface area of the firebox and riser. Furthermore, because a double bell is quite a bit more efficient as compared to its single brother, deduct 15% off the maximum ISA, which would be 4.675 m2 or 50.3 sq ft. The 1.5 barrel you are intending to use is roughly 2.5 m2 or 26.9 sq ft. The ISA you have available for the second bell is 50.3 - 26.9 = 23.4 sq ft, a bit smaller than the first bell.
See that the gases can stream from all sides into the exhaust opening to the next bell. When you aren't sure just use a larger diameter or a reducer of a larger diameter to the 6". The same goes for the exhaust to the chimney, this is just to ensure there won't be any restriction in there which could possibly slow down gas velocity. This is a very important point, the same goes for J-tubes: the manifold-ish areas where the gas stream need to change direction should be wider in order to avoid friction losses.
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Post by erikweaver on Jul 19, 2015 5:41:33 GMT -8
Thank you, Peter. I knew I was missing something, but didn't know what. Now I feel like I'm pointing in the right direction again, and able to get back to laying this out.
I hope you write a book on this topic at some point, I'd like to buy a copy!
For my test system that I burned last winter, I cut a square hole roughly 12x16 inches in the lower-rear side of the bottom barrel (the half barrel), building up the interior bottom slope to this hole with perlite-clay mix (so that the perlite-clay floor sloped from a high point at the firebox, to a low point at the 12x16 hole); I then used hardware wire/cloth (1/8 inch squares) to form a shape going from square to round, held together with wire threaded through the edges, and all covered in a fireclay-cob mix to seal it; which allowed me to attach 6-inch chimney pipe to this manifold; this wired clay shape is about a foot deep/long I would guess, and it seemed to perform well.
Perhaps this time, it would be easier to keep the same idea of sloping the bottom barrel toward this 12x16 inch opening, and build the second bell in such a manner this dumps the hot air into one of the sides of the second bell, somewhat above the floor.
For my chimney pipe connection (from second bell, to through the roof connection), several options come to mind. Are any better than others?
1. I could simply plumb the chimney pipe to enter the top of this second bell, with a flange/reducer fitting at the bottom of the chimney pipe (8-to-6 inch reducer, 6-inch chimney pipe through the roof), perhaps 6-inches above the floor of the second bell;
2. Almost the same idea, but run 8-inch chimney pipe into the second bell (through the top) and above the bell reduce to 6-inch chimney pipe and run that through the roof (8-inch dia. pipe inside the bell, 6-inch dia. pipe outside the bell);
3. At the bottom of the second bell, build a small manifold off the side, and fit the chimney pipe to this (fitting the manifold to a 8-to-6 inch reducer, and 6-inch chimney pipe through the roof). I would have to add the increased ISA to the calculations, and the chimney pipe would not be running through the hotter portion of the bell on the way out (I'm uncertain if this is a good thing or not: if routed through the interior of the bell it would obviously pick up more heat on the way out; less so if routed to the roof along the outside of the bell).
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Post by peterberg on Jul 19, 2015 7:29:13 GMT -8
The manifold of your test system has been spaciously, that's a very good thing. Keep doing that, this will avoid friction areas.
Both #1 and #2 has the disadvantage of keeping the pipe warm in the bell itself. By doing this you could make the bell wider than the recommended maximum but don't ask me by how much, you would be the first one to test this out.
#3 is better in a number of ways. It won't pick up heat out of the warmest part of the bell, and you are creating the possibily of a bypass at the top of the second bell. In order to implement that, place the same reducer near the top of the bell and connect to the chimney pipe coming from below by means of a T-piece. Inside the T there need to be the bypass damper in order to be able to close this gas route when the chimney has warmed up sufficiently. The t-piece itself doesn't need to be 8", it's only needed to get the heater started when it's wet and/or cold.
Hmm... part of the above could count as #4, I believe.
And for #5, when you don't like the pipe outside the bell, there always the possibility to insulate the part which like #2 is inside the bell. Could be done with double walled insulated chimney pipe.
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