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How the air source heat pump works

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An air source heat pump is able to extract heat from the ambient air even at low temperatures of down to minus 20 degrees Celsius. Even at this temperature, the refrigerant used will evaporate.


The refrigeration cycle process as part of the mode of operation

An air source heat pump uses the ambient air as a heat source to supply heat to an entire building. In operation, a built-in fan actively draws in air and channels it to a heat exchanger, the evaporator. Within this is a circulating refrigerant, the physical state of which changes at low temperatures due to the thermal properties. When it comes into contact with the "warm" outdoor air supplied, it heats up until it ultimately begins to evaporate. Since the temperature of the resulting steam is still relatively low, the steam continues to flow to an electrically driven compressor. This increases the pressure, which also increases the temperature. Once the refrigerant vapour has reached the required temperature level, it flows on to the next heat exchanger, the condenser. Here, it transfers its heat to the heating system and condenses.

The heat gained in this way can be used for heating or domestic hot water heating. Before the cooled refrigerant can be reheated and compressed again, it first flows through an expansion valve. This causes the pressure and temperature to drop to the initial level, whereupon the cycle can be repeated.

Air source heat pump

Air source heat pumps utilise free energy from the ambient air for heating. They are ideal for modernisation projects, and allow for flexible siting. 

Heat from the air

[1] Vitocal air source heat pump
[2] DHW cylinder
[3] Heating water buffer cylinder

Heat from the air (with outdoor unit)

[1] Vitocal split air source heat pump
[2] DHW cylinder
[3] Heating water buffer cylinder
[4] Outdoor unit

Downloads on heat pumps

Optimised components ensure economical operation

Modern air source heat pumps from Viessmann are characterised by their very high efficiency and achieve a coefficient of performance (COP) of up to 4.0 at an outside temperature of two degrees Celsius and a flow temperature of 35 degrees Celsius. COP represents the instantaneous ratio of invested drive energy to useful heat generated. This high value can only be achieved by coordinating components. In this case, a power saving high efficiency pump, a variable speed fan, a compressor with anti-vibration mounts and an electronic expansion valve ensure the highest possible level of efficiency. Viessmann air source heat pumps are also among the quietest units available and are optimised for the use of self-generated power from photovoltaic systems.

Improving the life cycle assessment with green electricity

Heating with environmental energy is considered climate responsible. Depending on the output and outside temperature, only a fraction of the drive energy usually needs to be used in the form of electricity. For some time now, many power supply utilities have also offered special heat pump tariffs that are not only financially more attractive than standard electricity tariffs, but also more ecological. With the combination of an efficient air source heat pump and green electricity, system owners protect their own wallets and the environment at the same time.

Cooling with the air source heat pump

Even though the primary task of an air source heat pump is heating, it can also be used for cooling thanks to reversible operation. This ensures a pleasant living climate in all rooms, not only in the cooler months of the year, but in the warmer months too. You can find detailed information in the article on Passive and active cooling.

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