Experimental analysis of a R600 high-temperature heat pump in sub-critical and trans-critical operation

High-temperature heat pumps can provide process heat by lifting recovered waste heat to temperature levels needed for industrial processes. The application of a trans-critical cycle extends the operating range of a heat pump beyond the critical temperature of the used refrigerant. A prototype of a high-temperature heat pump using R600 was developed and investigated. The one-stage cycle uses a suction gas cooled reciprocating compressor, a low-pressure accumulator and an internal heat exchanger (IHX) for suction gas superheating. Experimental data of sub-critical and trans-critical operation is presented. In sub-critical operation, a coefficient of performance (COP) of 4.5 at a heat source inlet temperature of 60 °C and a heat sink outlet temperature of 110 °C and in trans-critical operation a COP of 3.1 at a heat sink outlet temperature of 160 °C was achieved. The measurement data further shows a dependency of the COP on the high-side pressure and suction gas superheating realized in the IHX.