Air heat pumps are among the most widely installed heat pumps in Germany. This is due both to their simple and rapid installation and to their relatively low investment costs. A conventional air source heat pump extracts heat from the outdoor air and raises it to the required temperature through the refrigerant circuit process. Depending on the model, appliances can be installed either outdoors or indoors. In the case of monoblock appliances installed outdoors, the refrigerant circuit is completely built into the heat pump. The generated heating energy is transported into the building with heating water. With split heat pumps, the refrigerant circuit is separated. The heat is transported by refrigerant line to the interior of the building, where the evaporator heat exchanger is located. This guarantees that the outdoor unit is frost-free, even in the event of a power failure.
A special form of air source heat pump is known as an extract air heat pump. Instead of outdoor air, this heat pump uses the extract air from rooms, which tends to be much warmer. This means that the compressor has less work to do to reach the required temperatures. The air volume is usually limited, however, which means that mono mode operation is not possible. As a rule, these types of heat pump are used for very small heat loads.