Thermo-economic and environmental analysis of various low-GWP refrigerants in Organic Rankine cycle system

Among various techniques of utilizing waste heat, ORC is receiving more and more attention for its high efficiency and flexibility. One of the toughest tasks in ORC waste heat recovery system is working fluid selection. The aim of the study is to investigate the effect of physical properties on overall ORC system costs and propose a general method of refrigerant’s performance assessment of ORC system. The internal relationship between the enthalpy of vaporization, molecular weight, and molecular complexity, and the impact on investment cost were analyzed theoretically. The analysis and experiment using R12333zd(E), R1234ze(Z) and R1366mzz(E) as well as R245fa explain the internal mechanism of the effect of different working fluids on NPIT, which represents the ratio of the net power output to the total cost. The economic performances of several new environmental-friendly refrigerants are evaluated using the NPIT assessment. The results show that R12333zd(E) has the best performance and its maximal NPIT value is 0.0625, followed by R1234ze(Z), R1366mzz(E) and R245fa. In addition, when R1233zd(E) performs excellently, evaporation and condensation temperature are 127 °C and 30 °C, respectively. The physical properties of R1233zd(E) and R245fa are extremely close, which makes R1233zd(E) be an alternative refrigerant without redesigning components of ORC system. NPIT is the answer to the challenge of complex boundary conditions and system types with various operational parameters and it could guide the selection of operating condition and design of ORC system equipment.