Ground & Air Source
A GSHP system consists of a ground heat exchanger, a water-to-water or water-to-air heat pump, and a heat distribution system. Generally closed-loop or ground coupled systems are used, where the ground heat exchanger consists of a sealed loop of pipe buried either horizontally or vertically in the ground. Most commonly GSHPs are indirect systems, where a water/antifreeze solution circulates through the ground loop and energy is transferred to or from the heat pump refrigerant circuit via a heat exchanger.
Overall efficiencies for GSHPs have generally been higher than for air source heat pumps because ground temperatures are higher than the mean air temperature in winter and lower than the mean air temperature in summer. The ground temperature also remains relatively stable allowing the heat pump to operate close to its optimal design point whereas air temperatures vary both throughout the day and seasonally and are lowest at times of peak heating demand. However both technologies are improving swiftly at the moment and claimed Air source efficiencies appear interesting.
Air Source Heat Pumps take energy from the air and raise it to a higher temperature, using a process which is similar to reverse refrigeration. They are similar to ground source heat pumps in terms of technology. With the ambient temperature as low as -15 °C, the system will still operate efficiently. The heat generated can be distributed either through water systems (radiators etc) or by circulating warm air. These systems can also be reversed to help cool spaces in periods of hot weather.
For more information download the Ground Source and or the Air Source FACT sheets