[Red Badger]

My idea years ago (I live in Florida) was to bury a matrix of 12" PVC pipes in the ground, deep enough to be below the water table (about 4' or deeper during dry season here) The temperature of the water is always about 68°F year round. A circulation fan would direct air through the pipes and back into the house duct system with appropriate dust and critter filters.......

[whd23]

That's the essence of a geothermal system. Constant ground (or groundwater) temperature. You basically have a big AC unit inside your house; during the summer months the hot side of the AC is the ground and the cool side is your house, in the winter it's reversed so it's as if you're trying to cool the earth.

I don't have the URL handy, but one site showed a unit being installed in a NYC townhouse! They drilled into the sidewalk to place the ground loops. The catch with geothermal HVAC is that the initial costs are huge compared to traditional systems. However, my mom's winter electric bill was the same as mine (geothermal "runs" on electricity) but I still had to pay for propane. Ouch!