Theoretical Performance Comparison of CO2 Transcritical Cycle Technology Versus HCFC-22 Technology for a Military Packaged Air Conditioner Application

Abstract

The world-wide agreement to restrict the use of chlorofluorocarbons (CFCs) and hydrofluorocarbons has prompted research into the possibilities of replacement refrigerants, particularly those occurring naturally in the environment. One such natural refrigerant, carbon dioxide, has been considered for certain refrigeration and air conditioning applications. In order to evaluate the potential performance of a refrigeration cycle based on carbon dioxide, a cycle model has been developed which can simulate the operation of a carbon dioxide based refrigerator/air conditioner. This model is called ACCO2 and accounts for the realistic effects of the thermo-physical properties of carbon dioxide. The model simulates the operation of a carbon dioxide based air conditioner that uses air as the heat source and heat sink. A parametric study has been conducted using ACCO2 as well as a validated cycle model which simulates the operation of an HCFC-22 based packaged air conditioner designed for use by the U.S. Army in a combat environment. The size and weight constraints of this application render HCFC-22 based units less efficient than typical HCFC-22 unitary air conditioners of the same capacity. It is hypothesized that these same constraints will not affect the performance of a carbon dioxide based packaged air conditioner as severely. The evaporative capacity, compressor power, and COP were calculated for each cycle over a range of indoor and outdoor temperatures, and used as a basis for comparing the two cycles.