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

A novel cogeneration system driven by low-temperature geothermal sources was investigated in this study. This system consists of a low-temperature geothermally-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger and a commercial R134a-based heat pump subsystem. The main purpose is to identify appropriate fluids which may yield high PPR (the ratio of power produced by the power generation subsystem to power consumed by the heat pump subsystem) value and QQR (the ratio of heat supplied to the user to heat produced by the geothermal source) 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 (pinch temperature difference in heat exchangers) and ηt (turbine efficiency) values play more important roles on the variation of PPR values. QQR values change slightly with various ΔTP, ηt and ηrp (refrigerant pump efficiency) 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.