I've been doing research over the last couple of weeks for setting up a geothermal heating and cooling system for my new greenhouse and pumpkin patch. One of the gurus for this setup (Sunny Johns) is right here in Colorado, but unfortunately his website isn't live anymore (read more below). You find tons of references to it however when reading on the subject.
Basically what I'll be doing is running a bunch of 4 inch pipes under the pumpkin patch about 3 feet down. I'll then run a pipe to the top of the greenhouse and in that pipe will be a thermostatically controlled fan. That pipe will go into the soil in one far corner of the patch and attach to those pipes that are running through the soil. That pipe will then pop out of the soil on the other far end of the patch.
What will happen, during the heat of the day, is that fan will suck the hot air at the top of the greenhouse and run it through the pipes which will heat the soil. Pumpkin roots like warm soil because it activates the biology in the soil. Then cooler air will be blown out the other end of the pipe system at the other end of the patch.
During the night, another thermostat will kick on when it gets too cool. This time the warmed soil with heat the cool night air in the greenhouse warming the greenhouse slightly during the night. The whole system is very inexpensive to run and efficient.
I own a website design business (www.pixoinc.com) and when I found that the Sunny Johns site no longer existed I decided to try the Wayback Machine. The Wayback Machine is an initiative where they crawl websites every so often and then store them. So you can literally see what a website looked like on a specific date. The cool thing is that the Sunny Johns geothermal site pages mostly still exist on the Wayback Machine so you can still get all of the good information that is posted there. Visit here.