When they installed our Geo-thermal heat pump, the installer told me the ground loop coils had to be 5 to 6 feet below the frost line. At our location in western Oregon, that is ~5 feet. At that depth, the ground temp here is about 52 degrees year round.
Our ground loop is 1500 feet of 2" PEX coiled in four "slinkies" that are layed in four 125 foot by 2 foot wide by 5 foot deep trenches. The fluid is a 15% ethyl alchohol/water solution.
The ground loop can also be done in vertical wells (even in your domestic water well) or in a pond or lake.
Thought you might be interested.
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If it's too hard to do, you are most likely doing it wrong. (Melvin Hill)
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If it's too hard to do, you are most likely doing it wrong. (Melvin Hill)