The refrigeration cycle requires there to be enough low temperature energy, from either the ground or the air, to turn the internal refrigerant from a liquid into a gas. Unlike water, which requires around 100 degrees to turn from a liquid into a gas, heat pump refrigerants can change into a gaseous state with temperatures lower than 0 degrees.
The refrigerant, although in a gaseous state, remains at a relatively low temperature until it is turned into a high temperature gas, through the use of the compressor. The compressor is the main piece of heat pump apparatus and is where the majority of the electricity consumed by the unit is utilised.
The high temperature refrigerant gas is then used to heat the requirement system or process, transferring the heat into a water circuit through a heat exchanger. As the heat is transferred the refrigerant condenses back into its original liquid form, from this point the cycle begins again with the refrigerant turning back into gas, utilising the energy source.
The typical energy balance is that potentially upwards of 4kW of heat can be produced by 1kW of electrical energy supplied to the unit and its subsequent compressor. The industry evaluation of this is a Coefficient of Performance (CoP) of 4, based on the ratio of 4:1.