Experimental Evaluation of a Charge Reduced Heat Pump Module Using 150g of Propane

A low refrigerant charge brine-to-water heat pump circuit was evaluated addressing a heating capacity of 5 - 10 kW and using propane as refrigerant. Propane is a natural refrigerant, has a low GWP (3) and attractive thermodynamic properties. Due to safety aspects the refrigerant charge was limited to 150 g, resulting in 0.45 kg of CO2 equivalent. The reduction of charge was achieved by minimized volumes of the internal components: the condenser and evaporator were chosen with an asymmetric plate profile, the liquid line was designed as short and thin as possible, the filter dryer in the liquid line was shifted to the suction line and the amount of compressor oil was reduced to its minimum. The charge reduced heat pump circuit was tested with different heat exchangers and two different compressors at various points of operation. This paper presents the results of the experimental evaluation and potentials for further optimization.