Coal Heated Cold Frame

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joeq
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Post by joeq » Mon. Sep. 28, 2020 2:14 pm

The title may be misleading, but I'm just throwing this out there for more experienced ideas.

In the very late winter I constructed this cold frame out of an old 4' square box from work, and a 4' picture window, saved (for about 30 years) from a salvaged picture window. The Mrs. was growing plants from seeds in the dining room window, and I had a brain-fart, to marry the 2 mentioned above components, and keep it all outside. All in all it worked out OK, but (as usual), I complicated it, maybe over did it, and went as far as to add irrigation, and electricity. I suspended it, (Only because I acquired it as a solid wood box) and because it already had 4X4 runners attached below, which made it easier to lift and move. I also raised it a bit more, by putting it on cinder blocks mostly to avoid the discomfort of bending down when tending to. And also had to protect and insulate the floor and sides from the added moist compost. It may be time limited, but I thought I'ld give it a try.
Here's a few photos nearing it's completion, and installation to the back yard.
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Those are older photos, and the unit is pretty much finished, 'cept for some interior and exterior trim, and was functioning in the early spring, but when the wife's plants went in, and her worries of a freezing night was a concern, I would fire up a small portable propane heater, and hang it inside. It seemed to do OK, but here is the main reason for this thread.

In the winter, I was thinking of maybe trying to grow something like spinach in there. (Just for the curiosity or entertainment of it ;) ) If my G111 is up and running, I was wondering about night time heating with coal, or even coal ash, instead of burning propane. Maybe sprinkling hot coal ash around the edges of the interior? but I would think it would cool down too quickly, or accumulate too much in time. Or have a metal pot, or pail, to put some burning coals from the111 firepot, located in the corner inside the cold frame. Or last but not least, building some sort of coal bed "under" the unit, in a barbeque grille. then again, it might burn the cold frame down to the ground.(Cooked spinach :D ) I've seen green houses with outside stoves, and heat ducted inside, but not sure if I want to go that route. just thought if I already had a burning coal bed in the 111, maybe I could utilize some of the leftovers, or burning coals, to add a little night time warmth to the cold frame.
Has anyone here had any experiences to offer, and any opinions? Would be greatly appreciated.

 
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warminmn
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Post by warminmn » Mon. Sep. 28, 2020 2:34 pm

Gallon jugs with hot water in them works fairly good for keeping it from freezing but I cant tell you how many as I havent done it in 6 years. Dont let me stop you from trying other things though.

 
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Post by Holdencoal » Mon. Sep. 28, 2020 2:46 pm

I think some in Holyoke mass beat you.


 
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Post by joeq » Mon. Sep. 28, 2020 2:56 pm

Thanks for the reply Warm
I've heard about these type of heat sinks too, but as you can see from the photos, there's not a lot of space inside. I could stack the jugs, I guess, but they would tend to cool down, and maybe freeze in time? I like the idea of throwing some burning chunks of coal into a metal pan, cause I think there would be more heat, in a smaller amount of space. But even that would cool in time. If I insulated the hot coals with ash, maybe they would stay hot longer? Through the nite?

And in reference to the video above, very interesting. Looks like he's pretty into it. Good tips. Thanks.


 
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Post by Lightning » Mon. Sep. 28, 2020 5:53 pm

joeq wrote:
Mon. Sep. 28, 2020 2:56 pm
I like the idea of throwing some burning chunks of coal into a metal pan, cause I think there would be more heat, in a smaller amount of space. But even that would cool in time. If I insulated the hot coals with ash, maybe they would stay hot longer? Through the nite?
Hmm... I take it that this unit is free standing outside and somewhat sealed?? I would tend to think that a couple burning embers would change the atmospheric composition of your little biosphere in there. I don't know if that would negatively impact the plant life or not. Other than that, hot coal ash doesn't have much mass to it. In my opinion it would cool quickly. I like the hot water bottle idea because there is substantial heat retaining mass there. If you could heat up some bricks in your stove, or on your stove, that might work even better.

 
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Post by joeq » Mon. Sep. 28, 2020 6:50 pm

Now there's an idea Lee. Heat some small red bricks, have a couple small metal trays in the corner of the cold frame, and at night, bring the bricks outside from the stove, drop them into the pans, with a few chunks of LeHigh on top for good measure. :annoyed:

 
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Post by Lightning » Mon. Sep. 28, 2020 6:57 pm

Right.. heated mass is what you need for that.. in the video the guy said he kept it 29 degrees in there while -7 outside. It was from all that warmer water in those tanks. Warm mass, and lots of it.

 
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Post by joeq » Mon. Sep. 28, 2020 7:35 pm

Lightning wrote:
Mon. Sep. 28, 2020 6:57 pm
Warm mass, and lots of it.
And so lye's the dilemma.


 
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Post by Lightning » Mon. Sep. 28, 2020 7:48 pm

So heat some bricks up with that nice stove ya got.. maybe you could put them underneath it.

 
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Post by joeq » Mon. Sep. 28, 2020 7:57 pm

That was one of my ideas in the 1st post, Lee. Not sure how well that'll work outside tho. Or how hot the bottom would get. (Made of wood.)

 
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Post by LeoinRI » Tue. Sep. 29, 2020 7:14 am

Joe,

Water has a specific heat almost 5x of brick. So lets say you load up 2 5 gallon jugs (83 lbs) of water at 150F and put them in the cold frame for the night, and the water is at 50F in the morning. If my research and math are correct 8312 BTUs are released. 83 lbs of brick at 500F dropping to the same 50F releases 7509 BTUs.

 
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Post by Lightning » Tue. Sep. 29, 2020 1:09 pm

He's right.. water has superior heat retention. That would be the ticket..

 
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Post by joeq » Tue. Sep. 29, 2020 5:21 pm

Wow. That's an interesting, and surprising bit of stats. Two, 5 gal. buckets in that little cold frame, is a pretty big foot-print. But I get the idea, and maybe can finagle something to fit, that'll hold water. Thanks for that Leo.

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