On the Use of Thermal Storages in Low-Capacity Heat Pump Systems

The paper proceeds from a hardware-in-the-loop experimental campaign on the operation of an air-source heat pump for heating a reference dwelling in Pisa, Italy. The system performances suffer from typical oversizing of heat emission devices and high water-supply temperature, resulting in heat pump inefficiencies, frequent on-off cycles, and relevant thermal losses on the hydronic loop. An experimentally validated heat pump model under different supply temperatures and part-load conditions is used to simulate the installation of a thermal storage between heat generator and emitters, in both series and parallel arrangements. Results show that the presence of the thermal storage in series configuration ensures smoother heat pump operation and energy performance improvement. Preliminary guidelines are proposed for correctly sizing the tank in relation to the heat pump capacity and the average daily heating load of the building.