1mind
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Posts: 3
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Post by 1mind on Dec 5, 2009 23:02:49 GMT -8
I'm building a 1000 sq. foot greenhouse with a heavily insulated perimeter (R 40)two feet down into the ground, making the entire mass of the soil in the greenhouse a thermal battery. The pipe will be covered with six inches of stone on all sides, then a long water pool will be constructed over the pipe enclosure, providing extra heat storage and the potential for aquaculture.
I'm planning on using a 8'' stove pipe and a 55 gallon barrel. I want to be able to keep 650 gallons of water, 5 tons of stone and 3 tons of soil at least 65 degrees. Though I've got significantly more thermal mass than normal, I'd like to not have to burn the stove all day every day to keep things up to temp. I'm looking for suggestions on how to get the system more powerful than mentioned in the book (or if that's even necessary.) Seems like making a taller barrel is a common way to accomplish this, and I was wondering how high I can before some part gets dangerously hot (or what I can do to make it safe with the higher heat.) There's also making larger diameter pipe, but I don't know if that's been perfected yet, in the version of the book I read it was still just an idea.
I'm also wondering if anyone has any greenhouse specific considerations.
Thanks,
Eli
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Post by Donkey on Dec 6, 2009 11:27:56 GMT -8
Wow.. Ambitious but interesting project. I know of one other greenhouse rocket. He ran a pipe a couple feet under the beds to heat the soil. It worked as long as it was baby-sat. Maybe he'll see this post and pipe in.. ? Umm.. Shooting from the hip: You've got two base considerations. One, making much heat and getting it (relatively) undiminished to the mass. Two, placing as much heat as possible into the mass without killing the movement of the stove(maintaining draft). I'd NOT use the barrel, it's for heating up the air inside a space quickly, taking the edge off and all, But it will radiate heat away that would probably be better off dumped into your mass. A slightly taller heat riser wouldn't hurt any but really, that's about draft, not heat (necessarily). I'd insulate the bejeesus out of the fire guts, keep the heat inside the fire right up to where you want to use it. Keep EVERYTHING just as short as possible, short burn tunnel, short path to the mass, etc. I see no reason (besides cost of the parts) not to go for a larger system, ten inch seems appropriate (just guessing).. On the flip side, heat into mass... Lots of mass is good, but there's also the consideration of conductivity. Using a material with higher conductivity gets the heat into the mass faster, which means shorter piping. Seems like the water would be the best conductor for receiving the heat, it would then conduct into everything it's touching pretty well, also since everything the water is touching is very thoroughly in contact(  ), you've got good conditions for heating everything else too. On the other hand, the water will radiate away into the air faster than stone or dirt as well. If you dump too much heat out of the system, it will have trouble (or fail completely) rising up a chimney afterward, it will also cause a good deal of condensation. One fix (on the draft side) is to route the pipe back to the beginning and steal just a little heat near the firebox to keep the draft going. 'Course, this will toss out a little heat "off the top", but it seems to me that it could be less loss than if you try keeping it in the system in the first place, easier to meter too. Another possibility is to run the pipe horizontally out the side of the building and let flue gasses pour out onto the ground. This solution is dicey as you would have to rely (almost) entirely on the heat riser for draft. I've seen that with rocket stoves chimneys aren't always necessary, but they sure do help as long as there's enough heat left over to drive them. You will need to provide a way for condensation to get out. Not really difficult buried in the ground, much more difficult if you run piping in the water as I've suggested. Last thing that comes to mind.. Rocket stove feeds are small, even for a ten inch system. you might need to fiddle with ways to hold more wood. Something like what I've done with my stove here at home or perhaps in the direction of peterberg's stove. ?? Yeesh, long post. Your idea brings up a lot of issues I've been thinking about. Makes me excited and chatty... Anyway, looking forward to seeing your progress, if you would be so kind as to post it here. Welcome to the board. |
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hpmer
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Post by hpmer on Dec 6, 2009 14:36:56 GMT -8
Also, although not stove related, is to have lots of thermal mass that stores the solar heat, such as many 55 gallon barrels filled with water. The mass also helps keep the overheating down during the day. It is my understanding that water is much more efficient at storing heat than is stone.
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Post by woodman on Dec 7, 2009 6:27:55 GMT -8
I always thought it was rock first then water.
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Post by woodman on Dec 7, 2009 7:21:05 GMT -8
Would be a project to build a thermal mass collector into the floor of a sweat lodge type structure as an emergency shelter.
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Post by Donkey on Dec 7, 2009 8:50:36 GMT -8
Also, although not stove related, is to have lots of thermal mass that stores the solar heat, such as many 55 gallon barrels filled with water. The mass also helps keep the overheating down during the day. It is my understanding that water is much more efficient at storing heat than is stone. Heavier materials provide more storage per unit size.. Depending on the rock, it can hold more heat than an equal volume of water. Water is good because it has decent mass per volume, but that's not is biggest strength. It's more versatile than most other storage choices. It's got high conductivity, heats up fast, transfers heat fast. It fits any container fully leaving no gaps and can be moved around by convection for passive modes or pumps, etc. The downside of water is that it want's to get out of whatever you store it in, which presents a constant maintenance challenge. If the water freezes or turns to steam it can rupture it's container. Barrels are ugly, bulky, constantly in the way and don't make for good furniture or multi-use objects (difficult to stack functions). Pumps break down, thin hoses clog with hard water deposits. Lastly, water promotes life and depending on conditions, storage containers can turn into little biomass farms, producing sludgy glop that can compound clogging pumps, etc. |
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Post by ytksgmt on Dec 11, 2009 15:55:32 GMT -8
Liquid water may have the biggest capacity.
It's volumetric heat capacity is 4.186 J/(cm3K) at 25 Celcius.
iron ... 3.537
soap stone ... 2.7
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1mind
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Post by 1mind on Oct 17, 2010 19:26:23 GMT -8
Ok, so the greenhouse is built, and it's time to get a burn on for the winter. I've got 5/16" thick 10" diameter steel well casing for the heat riser and 12 feet of the pipe traveling through the bed. After that, I figure it will have cooled down enough that I can use normal 10" chimney pipe. I am planning on casting the J shaped feed/burn tube and am thinking to make them somewhere between 8-9" diameter, at least 1 1/2" thick. In your initial response (Donkey,) you recommended not using a burn barrel at all, due to it quickly dumping heat. If I insulated the beejesus out of the outside of the barrel, would there be any disadvantages then? Would you be concerned that the barrel could become damaged by heat over time? Thanks in advance, Eli
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Post by Donkey on Oct 23, 2010 11:21:59 GMT -8
Well, yeah, that would work fine.. But! The barrel is really MEANT as a quick heat-'em-up radiant surface. It presents some small challenge, which IS worth it, if you need the function.. But, if you don't need it, what's the point of having it? Easier to just run it through an insulated pipe to where you want the heat. One guy's opinion.. |
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1mind
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Post by 1mind on Nov 30, 2010 9:00:47 GMT -8
The reason not to use an insulated pipe that surrounds the first heat riser would be that it's freakin huge. Finding a pipe that's at least fifteen inches in diameter and a 1/4'' thick steel is no easy matter, (though I've been trying.) So the barrel is looking rather attractive right now. The other thing I am considering is using an old wood stove for my batch feed chamber. My question is, why not? Cut a hole lower down in the stove for the exit pipe (8 inch hole for the ten inch system), maybe cut a hole in the top for the top feed option (I was figuring 6 inches from the back.) I am planning on transition from the stove to the heat riser with refractory cement. My only concern would be that the metal heating and cooling would be different than the cement that surrounds it, thereby leading to making cracks or leaving gaps. Could I bridge them with a little high temp sealant? Would I want to a little refractory cement tube (8 inch) that sticks into the stove to make that transition? Anyways, sort of a fiddly point, but I've been appreciate the input, so if anyone's got any, bring it on. I'll be pouring cement soon, and then I'll start posting pictures.
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), you've got good conditions for heating everything else too. On the other hand, the water will radiate away into the air faster than stone or dirt as well. 
