Dynamic modelling of a dual-source heat pump system through a Simulink tool

In this paper, the performance of a reversible Dual-Source Heat Pump (DSHP) system, able to exploit renewable energy from, alternatively, air and ground sources, is evaluated by using Matlab-Simulink. The actual source exploited depends on a simple control strategy on the basis of the current external air temperature. Yearly dynamic simulations have been carried out by coupling the DSHP to a detached residential building located in Bologna, in which heating and cooling loads are strongly unbalanced, and coupled to a Borehole Heat Exchangers (BHEs) field. Different case studies have been analysed in which the length of the borefield has been modified. The obtained results show that an optimal switching temperature can be determined to maximise the Annual Performance Factor (APF) for a fixed BHE field length. Additionally, it has been demonstrated that DSHPs can be very useful in order to reduce the total required length of the borehole heat exchangers and, consequently, the associated costs, and to solve the problems linked to the ground temperature drift, which can be originated by the presence of an undersized borefield and/or by unbalanced building loads. As a consequence, DSHPs can be suggested for the retrofitting of traditional ground-coupled heat pump systems in presence of undersized BHEs.