We are all a lot more familiar with heat pumps than we realise. A refrigerator is a heat pump, a split air conditioner is a heat pump, a large commercial building or industrial chiller is a heat pump. A heat pump simply transfers heat from one place to another. In reverse, it can even cool.
In a renewable thermal energy system, the heat pump is the interface between the thermal source and the distribution system. It moves heat from outside to inside (heating mode) or from inside to outside (cooling mode).
Heat pumps are commonly named by their source and direction of thermal energy flow. For example, the standard domestic hot water heat pump is a form of air to water heat pump as it transfers heat from the ambient air and delivers it into the hot water storage tank. The building services component is then the hot water tap in your shower. Air to water heat pumps are also commonly used as pool heaters and for hydronic heating systems.
A split air conditioning unit is a form of air to air heat pump while a multi head split or VRF / VRV style unit is an air to refrigerant heat pump.
While air to ___ heat pumps utilise the ambient air as their source of renewable thermal energy and to date are the most common type of heat pump, they are only able to utilise ambient air as their thermal source.
Whereas, the lesser known water source heat pumps are applicable to almost all other sources of renewable thermal energy.
Water source heat pumps either source water directly from water sources such as surface water bodies or groundwater or via a closed loop heat exchanger. A ground source heat pump is a variation of a water source heat pump that has been modified to suit the unique temperature requirements of a closed loop ground heat exchanger.