Long term performance analysis of a Dual-Source Heat Pump system by means of the Matlab/Simulink tool ALMABuild

In this paper, the performance of a Dual-Source Heat Pump (DSHP), able to exploit energy from both air and ground, has been investigated through the Simulink toolbox ALMABuild. Two different control strategies for the external source selection have been implemented: with the first one, the ambient temperature is compared to a reference value (namely, switching temperature logic); with the second one, the heat pump is forced to operate in air-source mode and ground-source mode during the diurnal and the nocturnal hours, respectively (namely, scheduled times logic). The DSHP has been coupled to a building with unbalanced loads and to a Borehole Heat Exchanger (BHE) field, for which different total lengths of the borefield have been considered. The obtained results show that with undersized BHEs a DSHP achieves better annual performance with respect to Air-Source Heat Pumps (ASHPs) and Ground-Coupled Heat Pumps (GCHPs) coupled to the same borefield. In addition, a DSHP can reduce the ground temperature drift originated by undersized borefield and/or by unbalanced building loads. The paper shows how DSHPs can be selected for the replacement of traditional GCHPs in presence of undersized BHEs.