Comparative study of mid- and low-pressure refrigerants in heat pumps connected to district heating and cooling networks.

This study evaluates the performance and carbon footprint of medium and low-pressure refrigerants in heat pumps combined with district heating and cooling networks (DHCNs) using one-stage and two-stage cascade heat pumps (HPs). Among medium-pressure refrigerants, R1234ze(E) achieves the highest coefficient of performance (COP), reaching 2.78, and a combined COP (simultaneous heating and cooling case) of 5.17 in one-stage configurations. R513A presents the lowest COP (2.62) and, nevertheless, presents the highest heating capacity. In two-stage cascade configurations, low-pressure refrigerants R1233zd(E) and R1336mzz(Z) enable high-temperature applications with condensation temperatures of 130 °C. The highest COP in cascade mode is 1.64 for the R1234ze(E)/R1233zd(E) pair, and the highest combined COP achieved by the same pair is 2.68. Carbon footprint analysis highlights indirect emissions, with R450A/R1233zd(E) producing the minimum total equivalent warming impact (TEWI). The carbon footprint analysis shows the need to focus on the GWP value and the indirect emissions of each refrigerant.