The Internal Heat Exchanger in a Transcritical Co2 Refrigerator: an Experimental Study

The classical substances as Hydrochlorofluorocarbons (HCFCs) used as working fluids in the vapour compression plants have to be replaced by new substances because of their ozone depletion potential and their greenhouse effect. Carbon dioxide (CO2) is non-toxic, non-flammable, has zero ozone depletion potential and negligible global warming potential as refrigerant. Referring to a transcritical CO2 cycle working as a classical “split-system” to cool air in residential applications, the aim of this paper is the evaluation of the energy performances using an internal heat exchanger. The experimental plant employs a semi-hermetic compressor, plate-finned tube type heat exchangers, a back-pressure valve electronically controlled and an expansion valve. Besides it is possible to control the flash gas produced in the liquid receiver thanks to another semi-hermetic compressor linked to an inverter. An increase of the coefficient of performance has been found using the internal heat exchanger. The comparison of the coefficients of performance of two cycles, working with and without the internal heat exchanger, is discussed. Key-words: carbon dioxide, transcritical cycle, internal heat exchanger