Experimental comparison between different heat pump designs working with propane to control subcooling for sanitary hot water production.

Subcooling significantly influences the heat pump performance. An optimal value based on external conditions exists. In this frame, three different propane heat pump prototypes for sanitary hot water production, where high temperature lifts at the secondary fluid take place (so the benefit from high degrees of subcooling is maximized), have been tested. This work experimentally compares the two most interesting prototypes. The most important differences between both are the subcooling control (by a throttling valve in one case (10K2V) and by the expansion valve in the other (0K1V)) and the superheat control (by the expansion valve in 10K2V and zero in 0K1V). Results show the capability of both prototypes to operate with similar COPs than other leading systems based on transcritical cycles. COP differences up to 5.5% between both and the extra valve required in 10K2V demonstrate the importance of the configuration to develop the most thermo-economic heat pump solution.