Performance investigation of multi-stage saturation cycle with natural working fluids and low GWP working fluids

Improving the efficiency of a vapor compression cycle and using low GWP working fluids have become more important than ever due to the environmental concerns. A saturation cycle consisting of saturation compression and saturation expansion was proposed in order to improve a vapor compression cycle performance by reducing thermodynamic losses associated with single phase gas compression and isenthalpic expansion. The saturation cycle can be approached by multi-stage cycles with two-phase refrigerant injection. In this paper, the performance of saturation cycle was theoretically investigated for low GWP working fluids including natural fluids under ASHRAE standard operating conditions and extreme heating condition. The simulation results indicate that the benefit of using the multi-stage cycle is higher for the cycle with higher pressure ratio. When the saturation cycle technique (four-stage cycle) is applied, the COP improvements of D2Y60 (mixture of R32 and R1234yf), CO₂ and propane are 46.9%, 43.2% and 38.2%, respectively under extreme heating condition.