Parametric study of a novel organic Rankine cycle combined with a cascade refrigeration cycle (ORC-CRS) using natural refrigerants

This paper presents a novel design of a stand-alone refrigeration system consisting of a combined organic Rankine cycle and a cascade refrigeration system (ORC-CRS) for low-evaporation-temperature applications (from −55 °C to −30 °C). Natural refrigerants were used as working fluids: toluene for the organic Rankine cycle and NH3/CO2 for the cascade refrigeration system. A parametric study and a regression analysis have been performed to characterize the system and to estimate the overall system coefficient of performance (COPoval) and exergetic efficiency (ηex_oval). The highest values of COPoval and ηex_oval calculated were 0.79 and 31.6%, corresponding to ORC evaporation temperatures of 315 °C and 255 °C, respectively. Renewable thermal energy sources from 100 to 350 °C can be used to drive the facility, thus reducing dependence on fossil fuel and CO2 emissions. This stand-alone facility seems to be a feasible option to exploit low- and medium-grade thermal energy (geothermal, solar, waste heat) in places where the electricity supply is unreliable.