Abstract:

The aim of our study is to propose a theoretical model to analyze the energy efficient and environment friendly cascade system for various refrigerant pairs. In order to realize, the optimum cascade evaporation temperature (TOPT,CAS,E) which maximize the performance, COP values are determined for different refrigerant pairs of the system. After the optimization, two different cases have been investigated through a thermodynamic analysis to discover the best refrigerant pair for the system. Natural refrigerant CO2 is selected instead of R404A which has high Global Warming Potential (GWP) value for the low temperature cycle (LTC). On the other hand, synthetic refrigerants (R134a, R152a) and a natural refrigerant (NH3) are chosen for the high temperature cycle (HTC). In order to determine, an energy efficient and environmentally friendly cascade system, R134a/CO2, R152a/CO2 and NH3/CO2 refrigerant pairs are investigated in Case 1. On the other hand, R134a/R404A, R152a/R404A and NH3/R404A refrigerant pairs are investigated in Case 2. In calculations, the evaporation temperature (TE) is varied from -20oC to -40oC in LTC. The condensation temperature (TC) is considered to be between 30oC and 45oC in HTC. Mass flow rate requirements of systems for various refrigeration capacities (QEvap) are calculated for different refrigerant pairs. Moreover, the COPmax and total equivalent warming impact (TEWI) values of the system’s refrigerant pairs are evaluated and compared for various operating conditions.

Keywords: