Testing of a dual-source heat pump coupled with flat-panel ground heat exchangers

The paper reports and analysis the preliminary tests of a dual-source heat pump prototype (DSHP) as experimental air-conditioning system for a room at the University of Ferrara (UNIFE), Italy. The prototype is composed of a common air-to-air heat pump, a geothermal closed loop, and a novel kit for coupling the air-source heat pump with the closed loop. The kit links the refrigerant circuit with a plate heat exchanger coupled with the closed loop, and automatizes the switching between air and ground by mean of a control unit which pilots valves according rules based on air-ground temperature and air humidity. As ground heat exchanger (GHE), the Flat-Panel patented by UNIFE is chosen due to its higher performance in comparison with similar shallow and horizontal GHEs. Moreover, its flat shape allows installations in narrow trenches, minimizing the digging and therefore the overall costs. By mean of a comprehensive monitoring system, the behaviour of the duo prototype-closed loop was monitored for a whole year in terms of temperatures, pressures, flow rate, electricity supply, and heat flux. Even if the first year was used for the optimization of the switching rules, the comparison with traditional air-source systems evidences the better behaviour of the DSHP, and therefore the overall energy saving. Having the possibility to partialize the closed loop, the performance was also evaluated in under/overloaded conditions of the Flat-Panels, to implement new control criteria matching DSHP control rules with closed loop length for a dynamic design of the overall system.