In this part of How Geothermal Energy Works, we will review how geothermal energy is converted into useable energy through geothermal heat pumps.
A geothermal heat pump (GSHP) or ground-source heat pump is a heating and cooling system that uses the ground as source of heat during the winter and a sink for heat during the summer. Invented by Lord Kelvin in 1852, the heat pump was developed by Peter Ritter von Rittinger in 1855 and built in the late 1940s.
The GSHP combines a reversible refrigeration cycle with a circulating ground loop to provide heating or cooling. The key system of a GSHP is similar to that of an air source heat pump. However, in contrast to an air source heat pump, which exchanges heat with the air outside, a geothermal heat pump uses the ground for the heat exchange. A geothermal heat pump operates with an advanced efficiency compared to an air pump because the temperature of the ground is warmer in the winter and cooler in the summer than the air. Moreover, a geothermal heat pump enhances efficiency and reduces the operational costs associated with heating and cooling by taking advantage of the uniform ground temperatures of about 50-60 °F (10-16 °C) throughout the year. This temperature is maintained even at shallow depths of 5 to 10 ft. Not being weather-dependent allows a geothermal heat pump to be successfully combined with intermittent sources of energy such as solar to form a geosolar system that has even better efficiency.
The geothermal pump systems can reach 3-6 coefficient of performance (CoP) during the cold winter months, compared to a coefficient of 1.75-2.5 for air-source heat pumps on similar temperatures. In fact, geothermal heat pumps are considered to be among the most energy efficient HVAC and water-heating systems. The lowest coefficient of performance of a geothermal system (and that includes the power for the fluid recirculation through the underground pipes) is 2.5.