What is an Air Source Heat Pump and how does it work?

An Air Source Heat Pump (ASHP) is a system which absorbs heat at one place and releases it at another. This device is reversible, it can be used as a space heater as well as a space cooler.  An ASHP is composed of two heat exchangers, an evaporator and a condenser. 

An evaporator collects the heat from the ambient air, even at low temperatures. The evaporator contains liquid refrigerant and the heat transfers from the air to this refrigerant. The refrigerant’s temperature increases, allowing it to pass from the liquid state to a gaseous state. This gas is then compressed by an electrically driven compressor, and its temperature increases significantly. Then the hot gas refrigerant passes through a condenser where the heat energy is transferred to the fluid (air or water) used in the space heating system. Finally the cooled refrigerant turns back into a liquid state. After passing through an expansion valve it returns to the evaporator.

Air source heat pump
Air source heat pump