This is the device I plan to add to an existing heatpump for geothermal use. It will be added just upstream of the outdoor condensor coil.

It's original use is for heat recovery from the hi side of the AC system for domestic hot water.

http://www.acoverstock.com/ecu-heat-recovery-unit.html


Here in north Texas you need approx 400 feet/ton of horizontal pipe buried six feet deep where the temp is about 68f all year. A "slinky" of 3/4" black poly laid in a 3' wide trench is reccomended.