Enhancement of R-134a Automotive Air Conditioning System

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. Extensive results are presented pertaining to performance of the present baseline R-134a system, realistically enhanced R-134a system and the idealized R-134a system that gives an upper bound on the maximum possible augmentation from a thermodynamic point of view. The paper also provides extensive comparisons of the TEWI of the R-134a system with those of the proposed alternate systems, viz., the flammable subcritical systems (R-152a, R-290 and R-717), supercritical carbon dioxide (R-744) system and conventional open air (R-729) cycle system. Based on these comparisons, it is concluded that the enhanced R-134a system is the most pragmatic solution to deal with the issue of the automotive air conditioning system TEWI.