A STUDY ON THE PERFORMANCE CHARACTERISTICS OF CARBON DIOXIDE REFRIGERATING SYSTEMS WITH MULTI-SPEED TWOSTAGE COMPRESSION

摘要

The light-commercial refrigeration sector considers carbon dioxide (CO_2) as a promising naturalrncandidate to replace the conventional synthetic refrigerants, but performance improvements at the cycle levelrnare still required. The aim of this work is to investigate the effect of the compressor speed on thernperformance characteristics of CO_2-based refrigerating systems. To this end a variable speed two-stage rotaryrncompressor was installed in an existing experimental apparatus and an energy optimization exercise wasrncarried out. The optimum refrigerant charge and restriction for each compressor speed was experimentallyrnfound and compared. It was noted that Coefficient of Performance (COP) for the whole range of compressorrnspeed reaches a maximum at a single combination of charge and restriction. This suggests that a capillaryrntube may be used for metering the refrigerant mass flow rate in variable capacity carbon dioxide refrigeratingrnsystems, even knowing that at low speeds the evaporator heat exchanges will be negatively impacted by thernhigh evaporation pressures.