Performance Analysis of a Heat Pump Using Different Refrigerants to Supply Heat to Industrial Processes

In a coupled system heat pump-solar thermal energy, the heat pump represents 50 % of the total cost, while the compressor represents 92 % of the total heat pump cost. Refrigerant and mass flow rate directly determine the cost and the operation of the compressor. In this work, a thermo-economic study of a heat pump coupled to solar thermal energy was carried out to determine the minimum energy cost, depending on the mass flow, varying the degree of subcooling and guaranteeing for each flow rate and three selected refrigerants, the heat load and the target temperature required by an industrial process. The three selected refrigerants were: R600a (ODP=0, GWP=3), R245fa (ODP=0, GWP=1030) and R1234ze(Z) (ODP=0, GWP=1.4). A pulp bleaching process for paper production was used as a case study. The heat pump uses a network of low-temperature solar collectors as a heat source, it reaches a temperature of 70 and 80 °C and operates with an irradiance of 443 W/m2. For each refrigerant, the minimum cost was calculated based on the degree of subcooling and the mass flow rate. Refrigerant R1234ze(Z) produces the lowest levelized cost (LCOEt) of 0.06058 $/kWh with a mass flow rate of 1.33 kg/s, a subcooling degree of 9 °C and a coefficient of performance (COP) of 3.19. The highest COP was 4.01 for the same refrigerant with a subcooling degree of 30 °C. By varying the mass flow rate of the refrigerant R1234ze(Z), the total cost of the heat pump can be reduced by up to 7 % and using other refrigerants by up to 26 % (R600a). Determination of the lowest total cost of the heat pump by varying the mass flow of the refrigerant allows reducing the energy cost by up to 19 %, making competitive the use of heat pumps feed with solar thermal energy for heat production.