Air-source heat pumps have been used for residential and commercial heating and cooling for many years. Such units rely on air-to-air heat exchange through evaporator units similar to those used for air conditioners.
More recent heat pump technology relies on circulating a refrigerant through buried copper tubing for heat exchange. These units rely on the constancy of the ground temperature below the frost level (about 55°F) for heat transfer and are considerably more efficient than their air-source counterparts. They are known variously by such terms as ground source, earth-coupled, direct exchange or geothermal.
The most efficient ground source heat pumps use ACR, Type L or special-size copper tubing buried in the ground to transfer heat to or from the conditioned space. The flexible copper tube (typically 1/4-inch to 5/8-inch) can be buried in deep vertical holes, horizontally in a relatively shallow grid pattern, in a vertical fence-like arrangement in medium-depth trenches, or as custom configurations suited to the installation.
The number of manufacturers which can supply commercial and residential ground source units is constantly growing. Contact the Copper Development Association Inc. to obtain the current listing.