Selection of working fluids for a novel low-temperature geothermal-powered ORC based cogeneration system

A novel cogeneration system driven by low-temperature geothermal sources was investigated in this study, consisting of a low-temperature geothermal-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger and a commercial R134a-based heat pump subsystem. The advantages of the novel cogeneration system are free of using additional cooling water circling system for the power generation subsystem as well as maximizing the use of thermal energy in the low-temperature geothermal source. The main purpose is to identify appropriate fluids which may yield high PPR value and QQR value. Performances of the novel cogeneration system under disturbance conditions have also been studied. Results indicate that fluids group presenting higher normal boiling point values shows averagely 7.7% higher PPR values and R236ea and R245ca outstand among the group. ΔTP and ηt values play more important roles on the variation of PPR values. QQR values change slightly with various ΔTP, ηt and ηrp values while the variation range is larger under various geothermal source and heating supply parameters. Smaller ΔTP value, higher ηt value, higher geothermal source parameters and lower heating supply parameters lead to higher PPR values but lower QQR values.