ORC, R245fa, R1233zd, GWP, Efficiency
The majority of recently introduced ORC systems use R245fa as working fluid. The lower saturation pressures of R245fa versus R134a allowed the use of existing HVAC electric motors, compressors, evaporators and condensers after minor modifications as ORC electric generators, turbines/expanders, boilers and condensers. At elevated saturation temperatures R245fa turbine/expander equipment matches the power density of R134a HVAC compressors equipment. Refrigerants with still lower saturation pressures such as R123 and the newly developed low GWP fluid DR2 are excellent ORC working fluids but lack the synergy that exists in terms of power density between existing R134a compressors and their R245fa turbine derivatives. The use of these fluids in ORC applications prevents the use of existing HVAC compressor/motor hardware. Recently, a new refrigerant R1233zd has been introduced as a low GWP alternative for R245fa. This paper analyses the effect of this new fluid as a drop-in for R245fa into an existing 75 kW variable-speed, oil-free low temperature ORC system. The somewhat lower saturation pressure and vapor density of R1233zd allows a somewhat higher boiling temperature at maximum operating pressure, resulting in 8.7% higher cycle efficiency at equal capacity.