Testing a dual-source heat pump

Air-source and ground coupled heat pumps are depicted as energy efficient systems. Nevertheless, the ground coupling incurs in expensive extra-costs owing to the ground heat exchangers (GHEs), whereas the air exploitation suffers lower temperatures and frosting conditions. Coupling both solutions in a dual-source heat pump system (DSHP) can mitigate the former drawbacks. The present paper analyses the performance of a DSHP experimental prototype, installed as the air-conditioning system of a testing room at the University of Ferrara, Italy. The prototype is composed by a common air-to-air heat pump and a geothermal closed loop. The refrigerant circuit of the heat pump has been modified to couple on demand the closed loop by means of a plate heat exchanger. As GHE type, the Flat-Panel solution has been chosen due to its higher performance respect to all other horizontal and shallow exchangers. The switching between air and ground is automatized by mean of a control unit, according to the best thermal conditions, and the closed loop is also partializable to evaluate the length impact on the switching rules. The DSHP flexibility has allowed better performance than the original air-to-air heat pump, especially under hard weather conditions, and therefore an overall energy saving.