How it Works: Ground-Source Heat Pumps
Heating and cooling, courtesy of the earth.
Synopsis: A ground-source heat pump uses the relatively stable temperature of the earth below 20 ft. to keep a house cool in the summer and warm in the winter. It works by cycling a refrigerant back and forth between the ground and the house. In heating mode, the pump uses the ground as a heat source; in cooling mode, it uses the ground as a heat sink.
Left to its natural devices, heat energy flows from areas of high temperature to areas of low temperature. A heat pump reverses this natural process, absorbing heat from a relatively cool environment and moving it to a warmer area.
A window air conditioner is a common example of a heat pump. The interior of a room is not cooled by pumping it full of cold air; rather, it’s cooled by extracting heat from the room and dumping it outside. A heat pump can also be used to warm a room by reversing the process—that is, pulling heat energy from the exterior air and distributing it inside.
The flaw of air-source heat pumps (ASHPs), the most common type, is that their efficiency decreases with increased temperature extremes. The more frigid the air outside your house, for example, the harder the ASHP has to work to extract usable heat energy. That’s why many homes are relying on ground source heat pumps (GSHPs) for air-conditioning and heating at a higher level of efficiency.
Instead of air, a GSHP uses the relatively stable temperature of the earth as either a heat source or a heat sink depending on whether the system is in cooling or heating mode. Here’s how it works.
Heating and cooling, courtesy of the earth
Although the temperature of the upper 6 ft. or so of soil varies based on the air temperature, if you dig to at least 20 ft., the ground temperature is roughly equal to the annual ambient temperature at that latitude. Depending on whether the house’s heat-pump system is in cooling mode or heating mode, the soil is used either as a heat sink or a heat source.
For diagrams and more details on the refrigeration cycle of ground-source heat pumps, click the View PDF button below.