A comparative study to investigate two configurations of a two-stage evaporator in a CO2 heat pump chiller

Abstract

This study is carried out to investigate the performance of a CO2 heat pump chiller that provides heating and cooling simultaneously. For heating applications, hot water is produced at 90°C; while for cooling applications, chilled water is produced at 4°C. The evaporator utilized for chilled water production is a novel two-stage evaporator. Two configurations have been proposed to implement this two-stage evaporator in the CO2 system. One configuration is termed GFES: the first stage is fed by gravity; the second stage is fed by ejector suction. The other configuration is termed EDES: the first stage is fed by the ejector discharge; the second stage is fed by ejector suction. The primary goal of this study is to compare the performances of these two evaporator configurations and their effects on the system’s overall performance. To fulfill this objective simulation models are developed in Modelica. Results show that the COPs are nearly the same for both configurations. In addition, it is observed that the integration of the two-stage evaporator enhances the overall performance as the cooling capacity is shared between the two stages and the suction pressure of the compressor is elevated by utilizing the ejector.