The paper discusses the results of an experimental study carried out to investigate the performance and the operating map of a 20 kW air-to-water heat pump equipped with vapour injection scroll compressor and using R-407C as refrigerant.

Laboratory tests were conducted according to European Standard EN 14511 (2004) by means of a calibrated ambient room type calorimeter and a hydronic circuit that allow to maintain the heat pump working conditions to the desired value (air dry bulb and wet bulb temperature, water mass flow rate, inlet temperature and outlet temperature).

The results show that the heat pump provides, for every air dry bulb temperature considered, a heating capacity nearly constant as a function of water leaving temperature. Moreover, the compressor discharge temperature reaches lower values lowering air dry bulb temperature and this lead to an enlargement of the heat pump operating map, especially in the region of low air dry bulb temperature and high water leaving temperature.