Transcritical carbon dioxide small commercial cooling applications analysis

摘要

This paper presents a project to develop an R744 commercial single door bottle cooler that is cost competitive and matches the performance of typical cost optimised R404A and R134a systems. Compressors with different displacement and efficiency values are evaluated for refrigerating systems with fin and tube and steel wire-on-tube gas coolers. Capillary tubes are tested. A methodology to properly sizing them and to optimize the combination of capillary tube and refrigerant charge is developed. The problem of optimal cycle high pressure is addressed and Liao's approximated solution questioned. Tests demonstrate that the CO_2 energy consumption systems are higher than traditional ones especially at ambient temperatures above 25℃. Carbon dioxide appears to be a feasible option for stand-alone refrigerating equipment in terms of total equivalent warming impact (TEWI) compared to HFC refrigerants with actual single stage R744 compressor technology, only if the refrigeration units operate at medium-low gas cooler inlet temperature.