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Post by grizbach on Oct 2, 2014 7:02:37 GMT -8
Hi Greg,
You don't really want to go below 140F on your exhaust. Below that and too much condensation occurs, stalling draft. And draft is what you need for a rocket. So don't plug or slow down the flow!
If you follow the design, you will be happy with heat extraction.
Terry(hour N of Detroit)
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Post by satamax on Oct 2, 2014 9:20:39 GMT -8
three questions: *at what temperature (or temperature differential) does steam/smoke choose to fall, rather than rise? *any guesstimate for what kind of temperatures the exhaust would be, once exiting the house via the chimney? *how determined is heat to pass through the entirety of the chimney mass -- does it seek to equalize all mass materials via thermal bridging, before radiating into the house? Greg, you can have quick heat. You plonk a metal tank in front of your chimney, ane build the rockety in there, then, do a second bell in the fireplace/chimney. The plunger tube doesn't need to be insulated by cerablanket or the like. Rockwool is plenty good enough till 800C° even a thousand. May be even usual glasswool batt insulation could do the trick, if encased. You could even cook onto the metal tank. Smoke and steam would fall down if under the ambient temperature. Quite unlikely when you need to heat up! Exhaust is usualy from 60C° to 120C° if the rocket is tunned correctly. You mean will the heat, heat the whole mass of bricks evenly before radiating into the room? Nope! Bricks on top of the bell will always be hotter than the ones on the bottom. And since heat takes time to travel through bricks, it wont reach the great outsides that fast, before it has had time to warm you! If not a bench, you could always turn a wall of that mass into a settee back! A little check onto this site could broaden your views! heatkit.com/research/2009/lopez-rocket.htmAll i'm saying, is if i had such a nice fireplace/chimney arangement, it would alrerady be done. No messing, since it's soo simple and effortless! |
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Post by mrgregcrawford on Oct 3, 2014 16:00:43 GMT -8
this is a fantastic resource! love it.
perhaps its there... but on my first scroll through, i didnt see the heat dissipation over time. curious how long the bricks hold the heat, post-firing. also, my 110 year old chimney does have some hairline cracking already... which certainly is a concern.
great experiment. thanks for the link.
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Post by DCish on Oct 3, 2014 16:48:39 GMT -8
You might consider reading Into Evans' book (Rocket Mass Heaters 3rd Ed). Many of the basic questions are answered there. He says 2"/ hr heat travel for cob, 4"/hr for stone. I'd guess brick to be in the middle, but that gives you a range to start with.
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Post by satamax on Oct 3, 2014 22:37:56 GMT -8
this is a fantastic resource! love it. perhaps its there... but on my first scroll through, i didnt see the heat dissipation over time. curious how long the bricks hold the heat, post-firing. also, my 110 year old chimney does have some hairline cracking already... which certainly is a concern. great experiment. thanks for the link. Well Greg, i'm replying here, in public. It's better for future builders. As far as i know, there's only JRL's work which has been finished, retrofiting a fireplace with a batch and using it as a bell. I'm under the impression that i am the first one to have imagined this solution, but not sure. What gave me the idea is the french cantou www.google.fr/images?rlz=1T4SAVJ_enFR550FR551&q=cantou&hl=fr&sa=X&oi=image_result_group&ei=FIsvVNXzH5PlaLWRgaAF&ved=0CBQQsAQIt's a huge fireplace, where you have the fire in the middle, and two benches each side for the elders to sit on. It's big enough to make a single bell in it. The idea evolved and i've let it out when i saw people with useable fireplaces. Basicaly what the plan is; is to close the fireplace, to make a box, where the gases would gather and stay when hot. With a burner inside, for saving place or outside for better efficiency. And the plunger tube. That's a simple idea, instead of building the chimney on the side of the bell, why not put it where it's convenient, easy. A tube going to the floor, with insulation outside of it, so it's dosn't waste too much heat to power the draft, and you're done. Pish easy. You seemed to have a misconception about what the plunger tube. About your case, when you say from the plug down; you mean from the plug up? Anyway, the first thing to determin, is where to put the plug. In my drawings it's on top, but that isn't realistic. The first thing is to take your fireplace dimensions. Chose what system you want to use? Is it a batch or a J? What size? What are your need heating wise? 2700ft² you said, so big! And detroit is damp and cold in the winter? You said you wanted to be able to cook on it too. So you could do a bell extension in front, and use the later 8 incher from Peter. Since it seems to work soo well. www.permies.com/t/40007/rocket-stoves/Results-batch-box-thingy-InnovatorsBut it's getting a smidge more complicated. Since the riser is high. You would have to do something along thoses lines to house the riser. Top plate for boiling stews. The other one for normal cooking.  That in front of the actual fireplace, used as a first bell, and the fireplace used as a second bell. Can you access firebricks easily? A cast iron plate, or thick metal plate, real thick? I think in detroit, there's no prob. Tube for the plunger is no prob i would think. Insulation too, even glasswool would do if contained by aluminium foil and chicken wire for example. I woudn't worry too much about lining the chimney for the moment. First of all is to measure the fireplace and chimney both sides to know what are the possibilities. |
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Post by mrgregcrawford on Oct 4, 2014 7:19:45 GMT -8
about the plug up/down... it is assumed that i will need a liner from the plug up; but i ought to line the hot gases, keeping them off the already-degraded bricks of the chimney, from the plug down. or re-plaster the inside of the chimney (from the plug down). is this making sense?
i dig the french cantou. lovely atmosphere in there.
now, this is what i am thinking: a j-tube, outside & adjacent to one (herein referred to as the 1st) fireplace, made of repurposed firebrick (yes, i have a good source) & 55 gallon drum -- i have the materials for this already, and this will provide the quick-heat, as well as a cooking surface. the manifold will enter into the 1st fireplace, which has been sealed. and here it is... can i plug that 1st chimney, entirely/without a liner, and instead drop a liner down the 2nd chimney, into the 2nd fireplace, which is piped into the gas-chamber of the 1st? thereby, the hot gasses hang out in the 1st fireplace and in a portion of the 1st chimney, fall to the bottom where the ducting of the 2nd chimney picks it up and takes it outside. this is desirable, because protecting the brickwork of the 1st chimney is made much easier by not having to run the plunger tube through it. what do you think about all that?
sizing for heat: it would be absolutely miraculous to heat the entire 2,700 sq ft of the house with one RMH... this is not my target. for now, i would like the heater to be able to handle 3 or 4 standard-size rooms -- 2 off of the 1st fireplace, and the other 1 or 2 off the 2nd fireplace.
yes, i am wondering where to locate the plug. i will retrieve the measurements!
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Post by mrgregcrawford on Oct 4, 2014 8:55:49 GMT -8
very impressed by the 'batch-box thingy' you've linked. i usually am by 'the innovators.' i like the idea of doing a bell extension in front (materials as previously mentioned in last reply), and doing a later 8-incher a la Peter. wondering if the fireplace can act as Peter's 3rd bell...
i see the dimensions laid out in the link -- perhaps the mathematics will allow for a single bell (55g drum) which dumps into a 2nd (this being the fireplace), before going into the lined chimney...
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Post by mrgregcrawford on Oct 4, 2014 9:55:12 GMT -8
You might consider reading Into Evans' book (Rocket Mass Heaters 3rd Ed). Many of the basic questions are answered there. He says 2"/ hr heat travel for cob, 4"/hr for stone. I'd guess brick to be in the middle, but that gives you a range to start with. thanks DCish, but what i am wanting to know is how heat wants to move through the material in terms of: thermal contact conductance vs radiation; how determined is the heat, to heat the material before radiating (as satamax reiterated for me in a reply). thus, how far will the heat travel through the chimney (up and down), before radiating into the rooms? satamax feels pretty good about expecting it to not go too far before radiating. i would like to feel good about it too. especially because the chimney is enormous, and connected to the basement & outdoors. |
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Post by satamax on Oct 4, 2014 11:27:35 GMT -8
Mate, i'll read that later. It' nine thirty, an i'm drunk. So reading in english is hard.
I'va had probs with the place i'm tring to buy. And im' a bit down. So i'll reply tomorow!
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Post by DCish on Oct 6, 2014 13:15:20 GMT -8
Here is my thinking on the heat transfer question... I am very much open to correction by more knowledgeable others. As i understand it, heat moving by conduction moves at the same rate in all directions until it reaches equilibrium within the material (assuming perfect insulation of the material), or exits the material. When heat reaches the edge of the material it transfers to the next material at the rate of the slower transferring of the two materials. The denser the material, the closer the molecules within it and the more rapidly that heat is transferred. Air is less dense than solid and takes up heat much more slowly. Karl addresses the transfer of heat to air in this post ( donkey32.proboards.com/thread/1326/kind-weight?page=1#post-12875 ). A less specific, more rule of thumb type of number is given here ( www.cretepermaculture.com/2013/08/masonry-heater-3.html?m=1 ) claiming 1sq ft of surface area as good for radiating 185 but/hr for a masonry heater. So if you insulate the chimney, the heat will continue spreading throughout the entire chimney. If you don't, it will exit when it hits a boundary. When calculating how much heat will exit through the floor of a bell, Peterberg doesn't even factor the area of the floor into the calculation because the gasses at that level have a low enough temperature that heat transfer is negligible. If you consider that you might plug the chimney at, say, 5 feet up from floor level to make your bell, with 10' ceilings you'd have 5ft more for heat to travel before being lost to the room. Consider also that as heat moves up brick by brick, the face of each surface brick becomes a heat transfer surface. So heat must travel not only up, but also outward to keep up with heat being lost to the room. If you calculate brick at a (generous) 4"/hr heat transfer, it would take 15 hours for that heat to travel through the brickwork to the top of our theoretical 10' room... all the while losing heat as it goes. I believe Satamax is right. Even if you fired it for 15 hours straight you'd probably struggle to overcome the effect of such a large radiating surface. |
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jrl
Junior Member
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Post by jrl on Oct 14, 2014 9:40:17 GMT -8
Greg, for fuck sake! Please transform that into a rocket massonry heater!  Check this: www.permies.com/t/31382/a/13852/chimneybell.skp?download_attachment=trueYou replace the top of the bell extension in front of the chimney by a cast iron plate from a range, and you can cook on it!  Myself, i would do two sides. One with a batch rocket in the fireplace as JRL did. And make a range retrofit exhaust into the bell of the batch rocket. Not the safest option, may be. But i'd love that design. Is that chimney just a hollow brick structure? Or is it lined with a clay flue or channel inside? Is it just a single wall of brick? One thing to consider is brick/mortar is not usually 100% sealed if it's a single wall. With a plunger tube inside the main chimney cavity, you will probably have a heck of smokey mess in your house until the thing heats up, when cold starting. Once it's warm it will stay warm for 48 hours. As long as you fire it again within 48 hours you would have no smoke backing into your house. Any masonry heater owners here to comment on smoke backs with a single wall of brick? I like the idea of making the whole thing a giant masonry heater. I like the cooking surface in front of the bell as depicted above. I'd make the cooktop the first thing the exhaust hits and then channel it into the bell. A bypass damper could channel the exhaust away from the cooktop when you're not cooking (kids in the house?). A few batches a day and you'd be heating the room all day and night. Brick holds heat for a long, long, long time. My small (much smaller), rumford fireplace retrofit does well to heat my 12x14 living room all day and through the night on just an armful of finely split logs. A small fire at 7am and it's still 75 in the room at 7pm when I fire it up again. But, it's a much smaller application and it's a 5" CSA system. I'm also only using it in the fall and spring and only heating 1 room with it. I heat the house with a much bigger btu output coal stove in the winter. You, on the other hand, have brick exposed to the room on all sides and will get a tremendous about of convection/radiation into the room. Masonry heater/bell design, all the way! And definitely a batch box, don't even both with a J-tube design, IMO. |
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jrl
Junior Member
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Post by jrl on Oct 14, 2014 11:30:01 GMT -8
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