Due to the low purchase costs, the low installation effort, and the small footprint, air-water heat pumps are not only an attractive heating option in new buildings. Air-to-water heat pumps are also suitable for modernizing heating systems in existing buildings, provided the building has good thermal insulation.

How it works
Ambient air is drawn in via a fan and fed to the evaporator of the heat pump. Here, the existing heat is transferred to a refrigerant and compressed with the help of pressure, which results in a further increase in temperature. This heat is then transferred to the water circuit of the heating system via the heat exchanger, while the refrigerant, now cooled but still under high pressure, is expanded by the expansion valve.

Operating modes
The operation can be either in conjunction with panel heating systems or as a supplement to oil or gas heating, with the heat pump providing both domestic hot water and heating. Special models are also available for heating only the water circuit, the heating heat in this variant is generated by another energy source.

Installation types
Outdoor installation of an air-source heat pump
One of the great advantages of an air-source heat pump is its flexible installation. This is because an outdoor installation of the heat pump is possible if there is little space inside. For indoor installation, the unheated basement room is usually used to avoid condensation as far as possible. In order for the system to work effectively and to avoid thermal short-circuits caused by the intake of discharged air, a certain minimum distance must be maintained between the intake and exhaust air openings. Ideally, the system is installed in a corner of the basement, so that the two ducts can work orthogonally from each other. In the split version, cost and noise reduction can be achieved by placing the heat pump (inside) and the evaporator (outside) separately.

Advantages
Since the installation of the air-water heat pump eliminates the development costs for expensive digging and drilling work, the investment costs are relatively low compared to other heat pump systems. Approval procedures are not required at all. The small space required for the installation of the technology also makes the air-water heat pump an interesting alternative.

Disadvantages
A disadvantage of this energy source is the inconstant temperatures of the air. In unfavorable operating conditions, such as very cold winters, the effectiveness of the air-water heat pump is reduced. As a result, electrical auxiliary heating becomes necessary, which increases energy costs. The measure for the efficiency of a heat pump is the so-called annual performance factor. This should be at least 4. The fan that sucks in the air can cause noise pollution if it is installed in an unfavorable location. Therefore, the installation site must be selected with particular care.

Conclusion
Air-to-water heat pumps are an inexpensive alternative compared to other systems. Due to the low development and installation costs, they are therefore well suited for retrofitting as part of a modernization project. A price comparison of different specialist companies is worthwhile in order to reduce investment costs.