Thermodynamic analysis of subcritical High-Temperature heat pump using low GWP Refrigerants: A theoretical evaluation

An Industrial heat pump recovers low-grade waste heat from the industrial processes and upgrades it into usable heat, obviating the need for conventional boilers. The subcritical technique of high-temperature heat pumps (HTHP) has proven to be an environmentally friendly solution for a wide variety of industrial processes requiring temperatures between 100 °C and 150 °C. The purpose of this paper is to determine the feasibility of a high-temperature heat pump operating over a wide temperature range and utilising an eco-friendly working fluid other than the relatively high GWP R245fa. Environmental and thermodynamic characteristics of R1233zd(E), R1336mzz(Z) and R601 are evaluated and compared to R245fa. A steady-state thermodynamic model of a single-stage HTHP with an additional internal heat exchanger was developed to determine system operational constraints and assess the cycle’s energetic and exergetic performance. The minimum degree of superheating for dry refrigerants is mapped to assess the specific performance at different temperature lifts. The evaporator and condenser heat transfer coefficients are computed and theoretically analysed. The energetic findings confirmed that using R1233zd(E), R1336mzz(Z), and R601 as working fluids enhanced the coefficient of performance (COP) by up to 8.32 %, 11.68 %, and 19.61 %, respectively, in comparison to R245fa. According to the exergetic results, the compressor followed by the expansion process has the greatest thermal losses and therefore has the most potential area for future improvement. Furthermore, R1336mzz(Z) and R601 require larger compressor sizes when compared to R1233zd(E) due to their lower volumetric heat capacity value. Based on the environmental analysis of direct and indirect emissions, utilising low GWP refrigerant results in a significant reduction in the total environmental impact value when compared to using R245fa.