Transient model of a geothermal heat pump in cycling conditions – Part B: Experimental validation and results

The experimental validation of a transient geothermal heat pump model is presented. A commercial heat pump unit is fully instrumented to measure capacity and power usage by the compressor and the fan. On the refrigerant side, flow rates, pressures and temperatures are measured at various key points to capture the transient behavior under cycling conditions. Flow rates and inlet and outlet temperatures of the secondary fluids are also measured to check the energy exchanges at the evaporator and condenser. An uncertainty analysis shows that it is difficult to maintain a small uncertainty in such elaborate experiments. Eight cases corresponding to a combination of operating conditions are studied. In the four cases in which the unit was running in heating mode, it is seen that, contrary to expectations, the pressures equalize in the whole refrigeration circuit before the end of the off-cycle. Overall, there is a relatively good agreement between the model and the experiments.