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There is intense research activity to appraise the merits of the carbon dioxide (R-744) mobile air conditioning system due to its perceived amelioratory effect on the total global warming impact which comprises two components: direct global warming due to refrigerant leakage into the atmosphere and indirect global warming due to power consumption by the system. While the direct global warming impact of R-744 is negligible compared to that of R-134a, the indirect global warming impact of the R-744 system is intrinsically higher than that of the R-134a system. In order to quantify the indirect global warming impact of the R-744 system, an accurate assessment of its coefficient of performance (COP) vis-a-vis COP of the present baseline R-134a system is necessary.

The paper deals with potential augmentation of the present R134a automotive air conditioning system with the intent to lower its total equivalent warming impact (TEWI) which is a source of concern from the standpoint of environmental benignity of the system. It is identified that the most effective augmentation strategy includes (1) increase in compressor isentropic efficiency, (2) increase in condenser effectiveness, (3) decrease in lubricant circulation through the system, (4) decrease in air side pressure drop in evaporator through improved condensate management, (5) increase in condenser airflow, (6) decrease in air conditioning load via permissible increase in the amount of recirculated air through the passenger compartment and (7) reduction in direct emission of R-134a from the system through conservation and containment measures. The effect of each of these augmentations on the coefficient of performance (COP) of the system is quantified in a rigorous fashion.