Energy performance of a dual air and ground-source heat pump coupled with a Flat-Panel ground heat exchanger

A dual air and ground source heat pump can be an effective solution to improve the performance of a heat pump, by reducing the respective drawbacks of each individual technology. A dual source system in fact, allows a reduction in the size of the ground heat exchanger. Moreover, a dual source system can achieve a higher efficiency by switching to the more thermally favourable source, thus avoiding also the frosting/defrosting process of a common air source heat pump (ASHP). In the present contribution, the performance of a dual-source heat pump (DSHP) is numerically analysed. The building energy demand for both heating and cooling is estimated by means of the software EnergyPlus. Then, the resulting time series values are used as the boundary heat flux in modelling a ground heat exchanger. The commercial finite element method (FEM) simulation package COMSOL Multiphysics is implemented to simulate the heat transfer in the ground due to a horizontal ground heat exchanger (HGHE) in the shape of flat-panel. A function has been properly implemented in COMSOL to control the switching between air and ground sources, according to their temperatures. The DSHP shows a higher efficiency in comparison with an ASHP, due to the more favourable working conditions and the protection against frosting. In addition, a DSHP may represent a viable solution to couple the respective advantages of ground-source and air-source heat pumps.