Carbon dioxide-Way forward for the Refrigeration, Air Conditioning and Heat Pump Industry

Carbon dioxide (CO2) is a non-toxic, non-flammable natural refrigerant that does not contribute to ozone depletion and global warming. Unlike the familiar halogenated refrigerants, CO2 has a relatively higher saturation pressure at room temperature and a fairly high a critical pressure of 73.8 bar. Therefore, if CO2 were to be used in the standard vapour compression cycle the operation has to be in transcritical or in supercritical regions. Such operations bring in fluid behaviours and cycle control issues somewhat different to the experiences with subcritically operated familiar halogenated refrigerant. Being a natural fluid, CO2 is presently gaining an increased research attention for refrigeration and heat pumps applications. This paper attempts to present a general overview of CO2 as a refrigerant, potential applications, heat transfer behaviour etc., highlighting how it differs from common halogenated refrigerants.