Comparative study of combined organic Rankine cycle and vapor compression cycle for refrigeration: Single fluid or dual fluid?

Abstract Combined organic Rankine cycle and vapor compression cycle (ORC-VCC) systems for heat activated cooling are widely concerned because of their simple structures and convenient maintenance. According to the number of the working fluids, there are two different ORC-VCC systems, which are single-fluid and dual-fluid ORC-VCC systems. However, it lacks a deep understanding of their applicability. In this paper, using the geothermal water of 140 °C as heat source, the flash tank vapor injection cycle is coupled with ORC (ORC-FTVIC) in order to improve the efficiency. Meanwhile, four different systems of ORC-VCC and ORC-FTVIC based on single-fluid and dual-fluid are compared. Six kinds of working fluids are selected to analyze the effects of system parameters on the system performance. Taking the second law efficiency of thermodynamic as the objective function, the key parameters and working fluids of four heat activated cooling systems are optimized simultaneously and compared. When the heat source temperature is 140 °C, the cooling capacity of dual-fluid ORC-FTVIC system is maximum (2282.0 kW), followed by single-fluid ORC-FTVIC system (2177.5 kW), dual-fluid ORC-VCC system (2132.8 kW), single-fluid ORC-VCC system (1918.8 kW). The corresponding optimum working fluids are R1234yf-R152a, R1234yf, R1234yf-R152a and R1234yf, respectively.