Selection of a suitable working fluid for a combined organic Rankine cycle coupled with compression refrigeration using molecular approaches

Abstract

A vapor compression refrigeration cycle (VCRC) driven by an organic Rankine cycle (ORC) is an alternative to generating cold through a renewable energy source such as solar, residual thermal, and geothermal energy. The system analyzed in this work consists of an ORC coupled with a VCRC by a shaft where each one of the cycles uses an independent working fluid. This manuscript analyses 8 working fluids resulting in 16 combinations. These fluids include common refrigerants, such as R22 (HFCF) and R134a (HFC), with other low or null global warming potential (GWP) substances, such as hydrocarbons (HCs) and hydrofluoroolefins (HFOs). The PC-SAFT EOS is used as a predictive tool to obtain the equilibrium condition and thermophysical properties at each point in the cycle. The choice of the best combination of working fluids is done under the criteria that the ORC boiler and evaporator temperatures work in a range of 60.0 to 100.0 °C and −15.0 to 0.0 °C, respectively. The compressor outlet temperature, the VCR-ORC system Coefficient of Performance (COP), and the VCRC COP are the selected key parameters analyzed. The results show that the combination of n-pentane and R1233zd provide a good performance in terms of COP compared to other refrigerants.