Dynamic simulation and energy performance analisys of a dual-source heat pump

In this paper the energy performance of a dual-source heat pump (DSHP) able to use both air and ground as external thermal sources is analyzed by using TRNSYS17. The DSHP energy performance is compared with those offered by a conventional ground-coupled heat pump (GCHP) and by an air-to-water heat pump (ASHP) in order to evaluate the advantages obtainable with the use of a double external thermal source. Numerical simulations are carried out by coupling three heat pumps (DSHP, GCHP and ASHP) having similar nominal thermal power to the same residential building located at Bologna. By using dynamic simulations the seasonal and annual energy consumptions of these three heat pumps are calculated and compared. The simulations have been used in order to determine the best shifting strategy for DSHP between air and ground heat sources during the season in order to maximize the energy performances of this kind of heat pumps. As expected, the results show that the energy performances of DSHP are between the performance of GCHP and ASHP. It is demonstrated that the use of the ground during the winter can eliminate the energy losses and the problems linked to the cycle inversion due to the defrosting cycles and for this reason DSHP performs better than conventional ASHP. However, DSHP can become more attractive of GCHP because the use of air as alternative to ground allows a significant reduction of the boreholes size and, hence, a reduction of the investment costs. In addition, DSHP can solve the problem of the undesired ground thermal drift in buildings characterized by unbalanced winter and summer loads (with winter loads larger than the summer ones). A preliminary analysis about the economic convenience of DSHP with respect to GCHP and ASHP is also presented. This study has been conducted in the frame of the HEGOS (Heat pumps for EnerGy Harvesting Of Smart Buildings) project.