|
|
Post by pasto76 on Jan 3, 2012 8:17:51 GMT -8
I have available 2 inch landscaping rock, large chunks of concrete, pea gravel and crushed gravel. This is one part of the build for which I do not want.
I am thinking of using a crushed gravel as the material in contact with the duct, and having the 2 inch and larger chunks beyond that. I think doing that will maximize the surface area contacting the duct. The heat transfer from the duct is via conduction.
If you have any thoughts on that or experiences I would appreciate hearing them.
|
|
|
|
Post by canyon on Jan 6, 2012 11:57:03 GMT -8
These mass benches need to be monolitic. So, your rocks, gravels etc are great if you have sand in there to fill the voids. Otherwise it won't work effectively I found out first hand.  |
|
|
|
Post by pasto76 on Jan 13, 2012 8:51:37 GMT -8
Word. Im going to use road base or breeze, whatever is less expensive, to ensure monolithicity;0
|
|
|
|
Post by chrisz on Jan 13, 2012 10:18:34 GMT -8
along the same lines. . .
Is it acceptable / a decent idea, if I am going to be running metal chimney pipe verticle, to encase it in concrete block and then pack it tight with clay/sand or something like that?
The chimney will be in the garage going through an second floor (also garage space) and then through the "attic" and out.
I was thinking of encasing only the parts that are in the garage and the second floor room, for "thermal mass" and then running insulated pipe in the attic and out.
cz
|
|
bud
New Member
Posts: 11
|
Post by bud on Jan 13, 2012 16:46:24 GMT -8
since we're on this subject...
Is there any problem with heat flow through tubes in a vertical (upright) vs. horizontal thermal battery, then running the exhaust outside horizontally. I'm trying to avoid penetrations in my super-insulated roof.
|
|
|
|
Post by canyon on Jan 13, 2012 23:54:25 GMT -8
chrisz, No problem going vertical with your plan of packing tight with clay/sand as long as you can support that vertical point load without uneven settling or cracking of slab or whatever. In the straight vertical run as such the exhaust gasses establish a laminar flow so heat exchange is not so great but extra mass is extra mass and worthy, the question is whether it is worth the effort/expense versus stack robber for hot air during firing. The other thing is if you allow a vertical mass to go cold it could be a trick to get draft for lighting. Just some things to think about. Are you doing a mass bench before this stack? Bud, Would you give some more details about your situation? Do you not have room for a horizontal bench? One of the great things about the horizontal bench is that you are spreading the weight out so the psi is not so great and can be supported easier on existing floors vs. vertical where you need an appropriate solid foundation right from the ground. An insulated vertical stack outside could help the draft if you don't want it inside. |
|
|
|
Post by pasto76 on Jan 14, 2012 8:48:25 GMT -8
Canyon, wondering if you have any pics of some fins you've put on the duct inside the mass. Thats a good idea and want to do something like that.
|
|
|
|
Post by canyon on Jan 14, 2012 11:47:27 GMT -8
Canyon, wondering if you have any pics of some fins you've put on the duct inside the mass. Thats a good idea and want to do something like that. I assume you are talking about the turbulators which are just a strip of steel (stainless preferably) with the narrow width being 1/2 inch or so less than the id of the flue. You then take the strip and put one end in a vise and use vise grips on each side every 6 to 12" running the length to give it a twist like a corkscrew or you can bang it up with a ball peen hammer to give it an uneven surface that will break up the laminar flow. Heat exchange goes up dramatically and they are easy to remove for cleaning (can even assist in cleaning the flue). I don't have a camera at this point so I hope this suffices. |
|
|
|
Post by pasto76 on Jan 14, 2012 12:38:46 GMT -8
my apologies, I thought you had mentioned using a fin on the outside of the duct, extending into the mass to help transfer heat to the mass. I know someone wrote it, somewhere. Just not in this thread.
The turbulators are very interesting though! I have some metal with which I can experiment. Thanks!
|
|
bud
New Member
Posts: 11
|
Post by bud on Jan 15, 2012 20:45:05 GMT -8
Canyon,
To make a short story long, I have a timberframed farmhouse in N.E. Ohio, built into the hillside(lots of trees for firewood); the original part was built in 1816 with handhewn oak beams(avg 10 inch sq) as floor joists and 1.5ftx1.5ftx2ft sandstone blocks for the walk-out basement walls It had a loft which was expanded into a second story.
The "new" addition to the house was added in 1849, with rough-cut timbers, and concrete block foundation walls added under this "new" part in the 40's. The roof is slate over seriously under-engineered framing, so a new roof will be needed, which I intend to superinsulate, and through which I don't want any penetrations.
I want to avoid any heavy loads on the suspended floor, and I don't really care for the cob bench. I won't put this sort of load on 195 year old timbers. Part of the basement floor is still dirt, and I plan to put the mass heater in the walk-in basement, so I need to run the heat up through the floor into mass in the first-floor space. I am considering an all-firebrick mass heater with a large"firebox" along the lines of Donkey's "stove at home" that would serve also as the structural base for some upstairs mass. I'm looking for radiation(I have ideas for various "radiators") more than conduction heating. Being chained to a cob bench for 4 months a year if I want to avoid freezing to death in this climate ain't in my game plan (sorry if that's rocket heresy).
It may be an over-simplification, but as I see it, the significant advantages of a rocket mass heater are the internal chimney and the horizontal exhaust(low temps and no hole in my roof insulation). Apologies for the dissertation, but that's what I'm shooting for.
|
|
|
|
Post by pasto76 on Jan 17, 2012 9:44:14 GMT -8
also wondering if there is a practical limit to how far below the duct mass will warm. As it turns out, my duct is rather high, wondering if I need to build the top of the mass 1 foot or more, or if 6 inches would be ok.
|
|
|
|
Post by Donkey on Jan 17, 2012 21:03:18 GMT -8
Heat travels in ALL directions equally.
HEAT DOES NOT RISE!!!
Heated fluids will move by convection in a gravity well.. This is a property of fluids, not heat itself.
(can you tell this is a peeve of mine?)
|
|
|
|
Post by pasto76 on Jan 18, 2012 6:46:53 GMT -8
no your frustration is thinly veiled on that subject. Originally when I realized my exhaust would be 16 inches off the ground, I thought that since the mass is heated via conduction, no problem. then I start to worry....but no worries. Thanks
|
|
|
|
Post by Donkey on Jan 18, 2012 8:11:01 GMT -8
No sweat.. Umm... Wood doesn't burn either... |
|
|
|
Post by grizbach on Jan 18, 2012 10:26:06 GMT -8
Heat travels in ALL directions equally.HEAT DOES NOT RISE!!! Heated fluids will move by convection in a gravity well.. This is a property of fluids, not heat itself.(can you tell this is a peeve of mine?) Hey Donkey, My bench Is about 6 inches off the floor. I'll have to say after a few hours of firing the bottom is slightly warm and the sides and top can be almost hot. This is with the flue equal distance from the surfaces.  ?? |
|
??