The United States Department of Energy endorses geothermal heat pumps as an energy efficient option for consumers. By the year 2030, the Department of Energy forecasts geothermal heat pumps can provide as much as 2.7 quads per year of renewable energy. This is very significant as our annual energy appetite in the United States is 81 quads. The geothermal heat pump capitalizes on the stable earth temperature. Because the earth is cooler than the outside air in the summer, the geothermal heat pump has a thermodynamic advantage over air-source heat pumps and air conditioners. The process reverses in winter. The ground coil absorbs the heat from the earth and the system transfers it to the living environment.
Geothermal heat pump technology has made significant advances in the past few years. Installation initially was limited by the amount of space that was necessary for adequate ground-loop coil placement. Development of advances, such as the slinky coil, solved much of that problem..
A narrow trench is dug with a trenching machine and the heat exchanger pipe is simply spread out, almost as it comes out of the carton, and slipped into the trench. Trenching lengths have been reduced by two-thirds and installation costs reduced by thirty percent when compared with earlier designs.
The need to tear up a yard or a small lot to bury a heat exchanger coil need not stop the installation of geothermal heat pumps. Ground loops can now be installed without disturbing lawns and gardens and on small lots as well. This is done using a horizontal boring machine that pulls the loop into the ground as the drill string is removed.
Another advancement is the angle-boring machine. This machine allows earth-coil designers to drill multiple bore holes from a single location Not having to move and reposition the boring machine results in significant time and labor saving. Electric utilities and builders in several parts of the country have developed the concept of geothermal subdivisions to reduce installation costs.
In this example, PSI Energy in Indiana installed ground heat exchangers for a whole group of new houses before the houses were even built. The builders simply left the heat exchangers stubbed out inside the house along with the other utilities. The installing contractor then moved in a new heat pump, hooked it up to the heat exchanger and the power and the system was ready to operate. This approach resulted in a 34 percent cost reduction over the one-at-a-time loop installations. Average installed costs in 1995 ranged from $1,700 to $1,900 per residence with an estimated $400 per year energy savings per customer. Additional savings were realized due to the volume purchase of the heat pumps. Heat pump manufacturers have responded to these advances by bringing forth more efficient new geothermal heat pump designs with efficiencies comparable to an air-source heat pump with SEERs up to 16 to 20 and COPs up to 4 and above.