COP Improvement of a CO_2 Refrigeration System with an Expander-Compressor-Unit (ECU) in Subcritical and Transcritical Operation

摘要

One of the most attractive low GWP and zero ODP refrigerants is carbon dioxide (R744). The use of CO_2 in lowrntemperature stages of cascade systems is nowadays state of the art. If it is used in refrigeration systems with higherrnheat sink temperatures, e.g. supermarket systems, CO_2 has a disadvantage in terms of energy efficiency compared tornother refrigerants.rnOne possibility to improve the system COP is the introduction of a work extracting expander linked with arncompressor for a second compression stage. Such an option, an expander-compressor-unit, provides two advantages:rnthe system COP is improved and the discharge pressure and temperature of the main compressor become reduced.rnUntil now several expanders and expander-compressor-units have been proposed.rnIn this paper experimental results from several operation modes with an expander-compressor-unit (ECU) inrnsupermarket systems will be compared with a standard throttle process.