A friend/acquaintance of mine who lives a few miles from me built a setup based on this, here in southern Ontario. It's pretty neat. Big tubes into the ground and fans to run into/out of them to circular air from ground heat storage.

Ended up costing him quite a bit to build even though he did a lot of the work himself. But he does have a full season growing setup though, and a swimming pool in there. Not sure how much if any supplemental heating he uses; but he's got various citrus, bananas, etc. growing.