100 feet of 2 inch PVC pipe buried 4 feet underground
 

Hay Ron, I have installed a cooling system that works pretty well. It consists of 100 feet of 2 inch PVC pipe buried 4 feet underground in a closed loop ( the greenhouse is also underground). I use two small fans one to push the air into the loop and the second to pull air out. Going in, it has been as warm at 110 degrees, but it always comes out at around 60 degrees. Since it is closed looped I can also use CO2 and not worry about air lose. I thought I would pass this along to the list.

Tell me more. How large of an area are we talking about to bury the 100 ft. of pipe. Did you use a trencher to dig the hole. How big is your greenhouse and how cool does it get.