Exergy and energy analysis of a double evaporating temperature chiller

Temperature and humidity independent control (THIC) has been demonstrated as an effective way to improve the performance for air-conditioning systems. As an alternative option of THIC method, a double evaporating temperature (DET) chiller using zeotropic mixture refrigerants of R32 and R236fa has been proposed to substitute the traditional water-cooled chiller. The low temperature chilled water of 7 °C and high temperature chilled water of 17 °C will be produced simultaneously by this DET chiller, and the latent and sensible cooling loads of buildings can be afforded by the produced low temperature chilled water and high temperature chilled water respectively. In this paper, the experiments with different concentration ratios of R32 to R236fa are carried out on a 4.0-kW DET chiller. To further improve the energy performance of the DET chiller, the exergy analysis is used to investigate the effects of chilled water temperature and mass concentration of zeotropic mixture on the DET chiller. The exergy loss for each component is discussed in detail to identify the inefficient components, and then indicate the ways to improve the performance of DET chiller. The results show that the DET chiller achieves the lowest exergy loss and highest exergy efficiency when the mass concentration ratio of R32 to R236fa is 40%: 60%. Furthermore, the design temperature of high temperature chilled water should be at 16 °C to improve the energy utilization of DET chiller. This study will help to understand the design and operation for the DET chiller based air-conditioning systems.