Novel zeotropic refrigeration cycles for air cooling with large temperature decrease

Abstract

Refrigeration and air conditioning systems consume 20% of the overall global electricity. Developing refrigeration systems using zeotropic refrigerants is an effective approach to save energy in air conditioning systems, because the temperature glide of zeotropic mixtures can improve the temperature matching between the refrigerant and airflow. However, in air conditioning systems, the temperature variation of the indoor airflow is considerably larger than that of the outdoor airflow. Thus, a simple zeotropic vapor compression system cannot simultaneously match the temperatures in the evaporator and condenser. This significantly compromises the benefits of adopting zeotropic refrigerants. In this study, four new relay-evaporation cycles are proposed. They can simultaneously improve the temperature matching in the condenser and evaporator. Thermodynamic models of the proposed cycles using R32/R1234ze(E) are established, and their performances are compared to that of the single-stage and two-stage compression cycles in terms of the coefficient of performance (COP), exergy destruction, and temperature match indicators. Under the basic condition, the relay-evaporation cycles can improve the COP by 6.8%–16.0% compared to the single-stage compression cycle. In particular, the relay-evaporation cycle with a recuperator and an economizer exhibits 3.4%–6.6% higher COPs than that of the two-stage compression cycle.