Direct exchange geothermal (DXG) heat pumps exchange heat with the earth by circulating refrigerant directly through the ground through copper tubes. Two DXG units have been field tested in separate occupied residences in the Knoxville, Tennessee, area. Unit 1 utilized a pit with copper tubing laid horizontally at a depth of 4.5 ft (1.4 m) and has been tested over four consecutive heating and cooling seasons. Unit 2 utilized 5-3 ft (0.9 m) diameter vertical bore holes 13 ft (4 m) deep. A 10 ft (3 m) long, hollow galvanized steel cylinder wrapped with copper tubing in a spiral pattern on the outside was installed in each hole. This unit has been tested over three heating and cooling seasons. A flowable fill was used to surround the copper tubes in both ground installations. Energy savings ranged from 30% to 50% compared to the previous air-air heat pumps based on consistent degree-days. Neither unit required auxiliary heat at any time.

Units: Dual