Geothermal greenhouse

Wanted to start this to get some feedback. I am going to build a geothermal greenhouse this summer(20’x40’), has any one done this? Thinking about an underground heat exchanger, maybe like a 55gal drums full of aluminum cans. Most just use 4’’ drain pipe, but I think it that can be improved. Any thoughts?


Have you looked into building a walipini greenhouse? They are very interesting.

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Where do you live Al? A lot would depend on your average winter temps and number of sunny days and what you intend to grow in it.


I’m in WV, not the best for solar, that is why I am thinking of more heat sink to hold the heat for nights.

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Al, check out my greenhouse topic. If you gou a south faceing slope and good ground to work with its a good design. If not, this guy has a incredible greenhouse


Follow up video show the structure thermal-dynamic design details.
Show this is all off grid. With engine generator for mechanical systems powering at 4:42

Good find KristijanL.
I like that it is all above ground grade.
Here PNW wetside it is bad-bad to go underground. Energy kill your self de-humidifing for a wet-wet 50F.
Steve unruh


That’s a good sized greenhouse Al. Mine is only 10 by 20 but it was built mainly to do research in. Are you talking about a greenhouse or a hoop house? We have about as challenging a climate as you can have for greenhouse growing. Not because of the cold. Our average winter temps are in the Twenties, but because of the constant cloud cover in the winter. The last two years we have gotten more winter sun than I can remember but still we get at least five days a week with a dull grey low light sky because we are right off Lake Michigan. Many times we go for weeks with no direct sun. Heavily reliant on grow lights which was mainly why I came back to wood gas. The humidity here is somewhat like Steve described his. I get so much condensation coming off the ceiling when I run the heater that it like working in rain. I made most stuff out of concrete except the roof framing so I don’t have to deal with moisture rotting everything. I have a new design heater in my greenhouse but haven’t been able to use it yet. I have a six hundred gallon water tank built in there and I need to get it filled before I can run the heater to heat the tank. My other heater is a six inch rocket mass heater heating a 30 inch wide by 17 foot long grow bed. It’s not enough to keep my greenhouse above about 55 degrees in January. Good enough for root crops, lettuce and kale, but not much else.


I thought you were in Canada for some reason, but I suspect you get a lot more solar then in Michigan. :stuck_out_tongue:

Most thermal storage I have seen uses rocks or concrete. I get where you are going with it since aluminum conducts heat better. It is far more expensive then rocks unless you pick up a ton of free cans. And then i personally, would probably melt them and cast them into like bricks,balls or plates to achieve a higher density. aluminum cans have a bunch of plastic coating too. Putting them in a steel container will create die-electric corrosion issue.

But my question is whether you are trying to do a heat sink or do geothermal.

Here I just pulled this up around page 19 it has a brief table on the storage values of various solid materials, and it looks like you are on the right track.

They talk about aluminum oxide as well which would be in the slag. But around here I think it is 20c/lb for the slag or 40c/lb for the cans at the scrapyard. Because cans are a very thin layer of aluminum, about half of what you melt ends up to be slag unless you have a rotary kiln. Which is fine and dandy if you get that many cans for free. :stuck_out_tongue:

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Canada? really? :smiley: Any how, I just threw out cans as an example. Basically geothermal greenhouse is using the earth as a heat sink, blow hot air from the top down underground, then reverse at night. I am just trying to hold more heat.


Water has the greatest heat capacity of all materials. Why not use it? Its not nesseserly more complex neither.

Btw, l plan to join the greenhouse right on the south face of the house. Actualy l designed the house with this in mind.


Well don’t throw out the cans! Obviously they will work. :stuck_out_tongue:
but you are going to have to hook up with some heavy beer drinkers.
with a 50% yield of aluminum from melting down cans, you are going to need around 290k cans per cubic yard (~4500lbs)… On the bright side, it is like your own buried treasure.

It will work but most people use rocks and stack them inside the greenhouse for overnights. If you bury them and run air through them, you have to worry about the molds and stuff that can grow on them. but I have heard of people keeping their houses warm through winter by doing that.

Barrels of water will work as well too but you have to be careful if they actually freeze.

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I have about 8 inches of water in the bottom of my tank right now just to stretch the liner tight so I can seal around the water inlet for the heater. A few weeks ago we had about two weeks of temps right around zero F. With no supplemental heat and very little direct sun that water just got possibly a eighth of an inch of ice on top. I don’t think you would have to worry about barrels freezing but they take up a lot of room. Still, water is the cheapest and best way to store heat.


How about phase change salts? They were one of the leading candidates in the 70s - early 80s. They have the performance characteristics for greenhouse temps.

As said, water is hard to beat. And the obvious link to this site is to heat it with wood or other biomass, maybe with a charcoal producing burner in mind like Matt has demonstrated. Biochar is significant money, very little in the way of standards…

Greenhouses in northern winter climates I feel should be considered 3 season rigs. And given that in the summers things grow fine outside, 2 shoulder seasons really. Removable hoop houses can give good season extension.

Without artificial light, the solar power is mostly gone by October till March, might as well grow indoors under full artificial conditions.


Bout the same here Gary. I’m reworking my greenhouse right now switching over to more hydroponics, but I have enough LED growlights to cover the whole house. That’s about a thousand watts. Not real terrible on-grid but that’s providing power for that load for 12 hrs everyday off-grid. That’s a strain.


Hi Al. I wanted to revive your thread. It’s been a year and since you mentioned it in the other thread I have some suggestions. I have friends that are in the business of selling produce they grow at Farmers Markets. They have extensive experience with hoop houses. If you wanted I can get you on our private site and you could do some brain picking. One thing I will mention is that one problem with common hoop houses using the inch and three eights top fence rail tubing is that they will not take a lot of snow load. A few inches of snow and even worse, any ice and it’s necessary to get that stuff off there. I have seen lots of on-line pictures of collapsed hoop houses do to snow loads.
You may not have come across this idea but it is worth considering for anyone interested in grow structures. Not only very strong but also less span between framing for the plastic covering.

Another video that may be of interest.


Hoops and homemade bender. 3 hoops make 20ft wide that pile will make 40ft long 4ft centers


keep the pictures coming please, Al.