How does a heat pump work?
Heat pumps convert low-temperature heat into higher-temperature heat, even in winter when it is well below freezing. This process takes place in a closed circuit and involves constantly changing the state of the working fluid (evaporation, compression, condensation, expansion). Refrigerators operate on the same principle to extract heat from inside and discharge it to the outside. By contrast, heat pumps take stored solar heat from the environment around the house - soil, water or air - and release it together with the input energy in the form of usable heat to the heating and hot water circuit. The heat pump operates on the basis of a working fluid (coolant) which changes state (liquid/gas) in a continuous cycle and absorbs and releases heat.
The heat pump cycle is essentially based on the Carnot cycle. Its steps are:
In a heat exchanger, the liquid refrigerant absorbs energy from the heat source (water, soil or air) and evaporates as the temperature rises.
In a compressor, the introduction of electrical energy causes the vaporized but still cold coolant to compress and heat up. The coolant leaves the compressor as a hot gas.
The hot gas flows into the liquefier, releases energy to the heating system, condenses and leaves the condenser as hot, liquid refrigerant. This energy heats the hot water for heating or domestic use to the desired temperature.
The hot, liquid refrigerant is transferred to the expansion valve. In the expansion valve, the pressure is reduced very rapidly. The temperature of the coolant also drops very quickly without releasing energy. The cold, liquid refrigerant is transferred to the evaporator and the cycle begins again.