Hey "greenhouse" folks wrap your head around this idea...

If a person had an 8"diameter column of air 160 ft deep into the earth and there was a greenhouse built over top of it....how much heat do you think they could exchange within a small greenhouse during Middle TN mild winters?

It's a cased well. If I were to stick a fan on top of the well and pull air out of the earth, can it be enough to make a difference inside the greenhouse? It will be a small greenhouse, 12x16, maybe even smaller.

Thoughts?

If anyone even cares to chime in at all I am "all ears".

Sure sounds good in my head. A fan that's roughly the same diameter as the well casing - pull air from the earth and increase/decrease temp in greenhouse...with a special emphasis on "heat".  I can live without a greenhouse in the summer and I'm certainly building it with winter in mind.  I'd have an average air temp of around 58.2 degrees in that column of air. Fans/blowers are cheaper than heating elements to run.

Any ideas would be appreciated.

Where the well is at is also a really good spot of the greenhouse I want to build.

Side note - The well is currently not being used. Previous owner switched to public and the well had to be unhooked from house. I will be getting the well operable again, put a pressurized tank in the greenhouse, and use well water for our gardens.  I'd probably put in a wood stove for those really cold nights for heat so a pressurized water tank wouldn't freeze solid. I currently burn 6 cords/winter to heat my home so I've already got the wood and am use to tending a fire. I'd expect the need to burn the stove no more than 20-30 days in the winter months.

Think it's possible to keep the inside of the greenhouse from freezing conditions just by moving heat from the air in the well?

You'd have to put a 6" pipe down to the bottom to allow for air flow and use a 6" fan to blow air down into the hole, with the exhaust coming out the 1" space around the 6" pipe.  I don't know if you'd get enough heat exchange with that, but it might work.

Another Idea is to pump up the warm 60F water from the well and circulate it around the greenhouse. Think radiant in floor heating. You could even pump and store the warm 60F water into tanks and they will radiate the heat.

If there is water down there water is the medium to use. Much better heat exchange and 1200 times the density of air... so much less energy to move water then air.

I was just thinking about this the other day. Since my well head is in my pump house, could I use the casing to heat up the pump house to prevent freezing? My well is 120 ft deep. If I were to circulate air in the casing would it bring up the heat in my pump house on those days that it is well below zero and I have an occasional freeze up? A solar panel with a boat bilge vent fan? In my greenhouse I have used a duct fan to draw heat from the peak to corrugated drain pipe under the beds to create a heat battery for the raised beds. Using the well casing for a GAHT in the pump house just might work.
Here is a link using well water but I was just thinking air within the column.
https://greenrisks.blogspot.com/2012/07/using-your-water-well-as-standing.html

To those that mentioned to instead circulate the water...

I had considered that, but in the grand scheme of things if I wondered how I'd recirculate the water vs discharging it out into the yard and making a skating rink.

I would have to design it in such a manner that I'd never risk contamination of the well.  I have great water in the well and plenty of it.  The water column starts at 160ft down and extends down to 200 ft (depth of well). I'd hate to think I'd recirculate potentially contaminated water back down into the well if I simply opened it back up to air by letting it discharge back down into the well head.

Let's just hypothetically assume I'd need to recirculate 50 gallons every 4 hours back down into the well. Contamination?

Personally recirculating water back into my aquifer worries me a bit. Probably one chance in a million but recirculating something that I don't want in my drinking water or my neighbors would make me procede with caution. With a GAHT they suggest perforated piping to allow for condensation/mold issues. I could easily slide two two inch pipes side by side down my casing for inlet outlet. Solid piping would keep anything out of my well that might get sucked into intake.

Robert Ray wrote:Personally recirculating water back into my aquifer worries me a bit. Probably one chance in a million but recirculating something that I don't want in my drinking water or my neighbors would make me procede with caution. With a GAHT they suggest perferated piping to allow for condensation/mold issues. I could easily slide two two inch pipes side by side down my casing for inlet outlet. Solid piping would keep anything out of my well that might get sucked into intake.

You know I just edited my post from a few minutes ago to bring up the idea of contamination. I then looked and you had mentioned it.

I have a lot of water under me, it's potable and it's good stuff. I'd never compromise that for heat. Somebody someday down the road will def be thankful for the resource in a big way.

How warm do you want to keep your greenhouse? Or more specifically, what do you want to do in your greenhouse, so how warm do you need to keep it?

Do you have good southern exposure? Solar gain might be easier and more effective than heating it.

If you just need to protect some of the plants from the coldest nights of the winter, putting an additional cover over them on those nights is pretty effective.

To do it with air, I'd definitely put a long pipe down into the well (4-6") and blow cold air down and let it get heated up by the casing on its way back up.  Just putting a fan on the casing won't suck much since there's no way for air to get down in there in the first place.

Putting two 1.5" pipes into the well with a U at the bottom connecting them could be a liquid option.  Have them go down into the water as deep as possible without hitting the pump.  Circulate water down and then up through a radiator with a fan on it.

Designing the greenhouse for heat retention will make a really big difference.  If you put my greenhouse in your back yard it would probably never go below 50 even without heat.

This is an interesting issue to have.
In Australia where I am, Bendigo, we have 46 C days and sometimes get a few days at miuns 2 thats all. To read of your problems is eye opening

Recirculating water is geothermal, and a so-called open geothermal is absolutely acceptable done right.

http://www.geothermalgenius.org/blog/are-you-in-the-loop-open-vs-closed-loop-systems-in-geothermal.html

It will take a lot of energy to pump and recirculate water, but easy to pump air into bottom of that hole and get 50 degree air coming up. That air will very moist, and will condense everywhere in the winter. You will get icy windows and will rot any wood that stays wet.