Viewing post #667703 by cycadjungle

You are viewing a single post made by cycadjungle in the thread called the greenhouse that never needs heating.
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Jul 26, 2014 9:47 PM CST
Lakeland Florida (Zone 9a)
Bromeliad Seller of Garden Stuff Vegetable Grower Tropicals Seed Starter Pollen collector
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All of my greenhouses are hand built with 4x4s, 2x6s, etc. and are much larger than this one. They range from 28x48x10 to 40x60x12.
This is my "experimental blue house" . My original idea is that blue cycads look green here in my part of central Florida because the rain washes off the wax that makes these plants look blue. All I did was bury 4 fence posts 12 feet apart and tack some plastic on the corners.
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Soon after I put this together we were about to have the coldest winter I have seen since 1983. I had to turn this into a greenhouse, which was easy enough, but then I had to figure how I was going to heat it. We were about to see 9 nights that would go into the teens F and my lowest low would go down to 15F, which is not expected here in Florida. I have small propane heaters for the larger greenhouses, but those cost about $24 a night, per greenhouse (4) to run. So I have set it up that small water emitters drop well water in the greenhouses, and that heats all of them at the same time. Since the water itself is free, it costs 50 cents each night to heat all the greenhouses. However, this one is not close to the irrigated area. I thought about running a hose under the wall of the greenhouse, but the hose froze up when I tried that.
I thought about using a black barrel filled with water to solar heat the greenhouse, but even that can go wrong. Many times around here, it will be cloudy and rain for up to 3 days before the freeze events blow in. That makes any solar heating devise useless. So, how could I heat this greenhouse in a way that never needed power, a machine, or anything that could go wrong in the middle of the night and ruin a bunch of multi $1000 plants.
Around 1984 I thought I wanted to be a contractor so I bought all the books I needed to study and get my license. In one of the books it showed how to build a Trombe wall on a house, which is a window on the south side of your house and more or less, you can heat your entire home with the electricity of one 4 inch fan. This south wall is filled with materials like brick, rock, or in this case, water bags, which are heated by the sun hitting the window, but the key was table that showed a btu rating for each material. I cubic foot of water, in the right situation would produce a constant 62.4 BTUs.
So, the $10 geothermal greenhouse heating devise that can never fail.

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I buried a 55 gallon drum mostly in the ground and covered it with a half drum that I had sitting around that normally would be a planting container. There are two small holes on each side in the lower barrel right above ground level. I also cut a 3 inch hole in the top. I filled the bottom barrel with about 40 gallons of water. The cold air in the greenhouse sinks to the bottom and goes into the small holes, the air is heated by the water, which is constantly heated by the ground. The hot air rises and goes out the top hole, and that creates a vacuum, which pulls in more cold air into the bottom holes. During a freeze of 15F, and for the last four years, for that matter, no plants even had tip damage. I went into the greenhouse when it was 20 outside and took some readings, the water in the barrel was 63 degrees and the air in the barrel coming out was 58 degrees, which apparently, is enough to heat this 12x12x6 mini greenhouse. This was just a prototype, but there are all kinds of ways to use this same kind of thing and heat huge greenhouses as well. Tom

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