Theoretical analysis on a variable interstage compressor matching CO2 two-stage refrigeration (VICMTR) system

Abstract

In the two-stage refrigeration cycle, the interstage volume ratio between the low-stage and high-stage compressors is closely associated with the operating conditions and will determine the seasonal energy performance ratio (SEPR). In this study, a variable interstage compressor matching CO2 two-stage refrigeration (VICMTR) system is proposed. Five common matching options can be achieved by switching on the on–off valves in pairs and starting compressor in a compressor unit. The performance of these matching options and application feasibility in several cities are theoretically studied. The results indicate that the optimum matching can be obtained for the maximum coefficient of performance, maximum cooling capacity per compressor and low discharge temperature, respectively. H2L7 matching can recover more expansion work from expansion valve Ⅱ compared with other four matching options (HxLy, x and y are the basic quantities of high-stage and low-stage compressors). When the evaporation temperature is –48 °C, the SEPR of the VICTRM system in Beijing is 1.141, increased by 0.21% ∼ 1.87% compared with traditional fixed interstage matching system, the annual energy consumption is 63187.2 kWh, reduced by 0.19% ∼ 2.96%. The VICTRM system with eight compressors is suitable for moderate and warm climate cities. The proposed system can adapt to the variable ambient conditions in a year.