Just like air-source heat pumps, ground-source heat pumps move heat from one place to another. The system includes a compressor, a closed loop of refrigerant, and an air or water distribution system—just like an air-source appliance. Water-to-air systems also have a heat exchanger and a forced-air distribution system. Instead of capturing latent heat in the air, a ground-source heat pump uses a ground loop that runs in horizontal trenches or deep vertical wells. An add-on component (called a desuperheater) can also produce domestic hot water. Ground-source systems can distribute heat via water or air. Most are forced-air systems, using ducts.
Ground-source heat pumps run on electricity. When combined with a renewable electricity system, they can make an extremely attractive heating and cooling package.
Manufacturers claim COPs as high as 5, making these systems very efficient. But there is a catch: Published COPs do not include the electricity needed to run the pumps that circulate water through the ground loops, so actual COPs are less—probably closer to 3. The initial expense can top $40,000 for a residential system, including excavation or well-drilling expenses and the heat-pump equipment.
Typical forced-air, ground-source heat pump equipment. In this case, the system includes a desuperheater to provide domestic hot water, which is stored in the tank on the right.