[diesel_john]

There specialized plastic tubing for that purpose 3/4" costs about $1 a foot. The fittings are heat fused in and cost extra. Special equipment is used to heat the tubing before assembly. For wells there is a u fitting for the bottom for example.

Heat Transfer is well documented but still depends on how wet the ground is. I think you have to assume that its going to dry out around those pipes. When your in the AC mode. The trick is you don't want to freeze the ground around the tubes in the heat mode. Because when the soil freezes it expands and loses heat tranfer, just like snow is an insulator compared to water. You will need a high flow pump to purge the air from the lines, the first time.

The geothermal heat pump furnaces can be a single packages unit, just hook up the (ecosafe)antifreeze lines to it, and the lines to the cold water heater. No refrigerant lines to mess with. The HVAC industry is very defensive about the degree of difficulty that it takes to install one of these units. So if you do it yourself your warranty wouldn't be any good. That bs. You should be able to go to home depot and buy one of these babies. And let the chips fall where they may. There is even a company called LOOPMASTERS that specializes in installing geothemal loops.