Instructables

how to use geothermal heat for a greenhouse?

Greetings! I would like to tap a geothermal heat source to passively heat my greenhouse, but I know very little about how this is done. Any ideas or suggestions would be appreciated!

76543213 years ago
Dig a hole in the middle of the greenhouse about 3900 miles deep. Heat from the core will make it nice and toasty in their. You might need a machine like in the movie Core, though...
7654321 76543213 years ago
there*
SaveOurSkills2 months ago

http://www.earthairtubes.com/

rickharris3 years ago
On the other hand most greenhouse have a problem during the growing season of shedding excess heat. (being solar powered).

Are you sure you need to access Geothermal heat?

Hey Rick, Don't forget that the earth maintains a constant temperature. Geothermal actually is an air conditioner in the summer. It's the best of both worlds.

FYI the DIY option you are looking for is called an "earth tube" and you can find some write up on "Build it solar"

http://www.builditsolar.com/Projects/Sunspace/suns...

RedMayor (author)  rickharris3 years ago
I'm really just trying to find as many options as possible- I have a regular heater out there right now, and it works fine, it would just be better if I didn't need to use anything electric to keep the temp. up overnight. Geothermal now seems like a lot more work and expense than I am willing to spend.
Ground sourced heating is not a power less system but overall produces more heat energy than it consumes.

lots of web sites available.

If you can drill a hole a couple of 100 feet deep almost everywhere there is significant heat in the ground. in some places very significant.
RedMayor (author)  rickharris3 years ago
I wonder if maybe a cold sink is a better bet? If I dug down several feet around the perimeter on the inside, maybe use a grate of some sort, but have a place for the cold air to sink into? I read about it in "Earth-Sheltered Greenhouses", and thought maybe that would be an easier solution?
I doubt that would be any easier than heating via ground sourced heat collection. In general most heat in a green house is solar sourced, during the warm to hotter months although they are significantly warmer even in winter IF the sun shines.

They loose heat very quickly - stand in it in spring and note what happens when the sun goes behind clouds.

Heating for 7 or 9 months of the year shouldn't be a problem so stopping heat loss in the other 3 months IS the problem - Insulation!

Insulating in winter with bubble wrap helps reduce heat loss
Don't forget that a geothermal loop is normally used during the summer months to draw heat not extract it.

Take a look at this idea. Essentially he is using a kind of geothermal.
http://www.undergroundhousing.com/greenhouse_book.html
RedMayor (author)  steveastrouk3 years ago
Thank you, that is on my reading list for today.
In your question you state you want to tap geothermal heat to passively heat your greenhouse. Unless you live in Iceland, Japan, Hawaii, or another geologically active region of the earth you likely will not be able to derive significant heat from the earth passively. As Steveastrouk mentioned, you could put it in a hole, which (if below the frost line) would help keep your greenhouse at the ambient ground temp (in MN it's about 50 degrees farenheit 4-5 feet down). I'm not sure how being in a hole would affect your greenhouse's ability to gather sunlight however. Probably negatively.

Depending on the size and seriousness of your greenhouse operation (aka. in your backyard vs. your own business) the installation of either a vertical or horizontal loop ground-source heat pump may or may not make sense. Ground-source heat pumps are not passive, they use electricity to pump a fluid through a compressor like a fridge, and thus extract heat. They are quite efficient if installed correctly, but the start up costs may not make sense for a small application. I would contact a local contractor and ask if they have experience installing GS-heatpumps (many don't, yet), before making a decision one way or the other.

Hope this helps.
RedMayor (author)  ATTILAtheHUNgry3 years ago
After I posted this, I spent a day researching, and it is simply not economical for us to do that right now. If I could use a heatpump to also heat my house, and the greenhouse would just be part of the route, then maybe. Thanks!
framistan3 years ago
Don't listen to everyone on this subject because most people have misconceptions on what the temperatures are UNDERGROUND. I tried to research this subject and could not find much about ACTUAL temperatures underground..... so i decided to install my own temperature probes UNDERGROUND at various depths and get my own readings! Here are the results of my experiment. ...... 6 inch depth 35f to 80f..... 1ft depth 40f to 79f....2ft depth 41f to 79f..... 4ft depth 47f to 72f.... 10ft depth 56f to 70f.... 20 ft depth 57 to 61f. ..... ... If you graph out this data you will see that the temperatures vary greatly from summer to winter at 6 inch depth... but at the 20 ft depth the temperature only varies 4 degrees ALL YEAR. This is real data measured over about 2 years. Another thing most people do not realize is that HEAT RISES OUT OF THE GROUND ALL WINTER LONG! It is not HOT heat that can heat an UN-INSULATED house... but it CAN heat your INSULATED house up to about 62 degrees with NO FURNACE. My house will stay above 60 degrees unless OUTSIDE temperatures go below 35 degrees. This means i COULD leave our furnace completely OFF in the months of Oct, Nov, Dec..... and also Mar, Apr, and may. I only really need to run it in the months of Jan and Feb. ( I live in the center of the USA in St louis ). The picture is of my temperature gauges showing my experiment setup.
temperatures.JPG
How did you bore your deep holes ?

The work you needed can be found in the pages of the book "Earth Sheltered Housing Design" - published by the Underground Space Centre of the University of Minnesota, written by Carmody.

Also the works of the late Malcolm Well often reference the data.

Steve
RedMayor (author)  steveastrouk3 years ago
I'm looking into "Earth Sheltered Housing Design" right now, thank you!
RedMayor (author)  framistan3 years ago
Thank you for all of this info! Great research!
rickharris3 years ago
A lot depends on where you live and what your budget is.

Ground source heating will keep the green house above freezing even during the winter. Lots of web sites but it's not cheap.
Putting the greenhouse in a pit is a lot cheaper....
seandogue3 years ago
A geothermal loop will need to be embedded in your property. A heat pump is then used to extract heat from the ground and deliver it to your interior space, or, during the summer months to cool it by reversing the process.
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