[AIVC, Air infiltration and ventilation glossary, 1992]:a device operating on a refrigeration cycle in which the evaporator is a water/refrigerant heat exchanger and the condenser a refrigerant/air heat exchanger. The circuit normally includes an arrangement which allows the refrigerant flow to be reversed thus allowing heat to be transferred in either direction. In one system, a number of small air/water heat pumps installed in various zones around a building are used to transfer heat into or from a common water circuit. Thus, heat unwanted in one zone may be transferred to another where it is needed.