Heat pump

The heat pump is not a pump in the strict sense of the word, but a system with the aid of which low temperature heat can be elevated ("pumped up") to a higher temperature level. The heat pump operates on the thermodynamic principle of a refrigeration system. It allows the exploitation of the energy provided by heat sources such as air, water and soil, and also the exploitation of waste heat from industrial processes.

A heat pump system usually comprises two heat exchangers (liquefier and evaporator), an expansion valve and a compressor. The circuit is primed with a liquid refrigerant which evaporates at low temperature and absorbs heat from its surroundings. The compressor then raises the refrigerant to a higher pressure and temperature level, after which it is fed through the liquefier, where it condenses. The heat released during condensation is transmitted to a heating circuit (see Circulator pump) In the final stage the liquid refrigerant is expanded in the expansion valve and the cycle starts anew. See Fig. 1 Heat pump

The supply temperature which is capable of being attained economically in hot water heating systems or service water supply systems can amount to up to 55 °C. Heat pump systems have so far been installed mainly for room heating, service water heating and swimming pool water heating purposes, usually in conjunction with conventional heating systems (as bivalent heating system).