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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 focus of the present paper is the energy efficient automotive air conditioning system, which ipso facto is also environmentally friendly from the standpoint of global warming impact. Two efficiency enhancement strategies are presented - one entailing the use of judicious amount of recirculated air and another relying on reduction in the amount of reheating of the chilled air employed in the conventional system. The first strategy, referred to as the air inlet mixture strategy, reduces the air conditioning load by mixing proper amount of recirculated air with the outside air. The second strategy, referred to as the series reheat reduction strategy, reduces reheating of chilled air under low to moderate load conditions. Analytical relations are presented for the determination of reduction in air conditioning load due to mixing of outside air with varying amounts of recirculated air as well as due to reduction in the series reheat.