Experimental study on a Dual-Source Heat Pump in ground mode to assess the soil thermal response by means of a Distributed Temperature Sensing system

In this paper, a Dual-Source Heat Pump (DSHP), able to exploit both aerothermal and geothermal energy sources, has been tested in ground mode to evaluate experimentally the soil thermal response in presence of an undersized Borehole Heat Exchanger (BHE) field. The field is instrumented with a Distributed Temperature Sensing (DTS) system, by which the geothermal fluid temperature can be measured over the entire length of the boreholes during the heat pump operation. The DSHP has been tested to reproduce the working profile of a heat generator coupled to a reference building, which has been numerically simulated by means of ALMABuild, a Matlab-Simulink tool. Three operating profiles have been identified within the simulation results to define three typical days of the heating season, characterized by different required loads. The results show that a DSHP operated in ground-mode and coupled to a borefield 50% undersized can meet completely the heating needs of a typical winter day, whilst higher building loads must be satisfied exploiting both air and ground sources. In this case, 80% of the undisturbed temperature of the soil can be recovered in an hour when aerothermal energy is extracted, thus the unit efficiency remains high and the investment cost is strongly reduced.