Nevertheless, the
performances of air-to-water heat pumps are strongly dependent on the external air temperature, which continuously
changes in time during the heating season. As a consequence, the good sizing of the heat pump, which is crucial in
order to obtain good seasonal performances, takes into account not only the building loads, but also the climate of
the location where the building is located and the kind of control system of the device, which is responsible of the
heat pump performances at partial loads.