However, with some reasons including the above, the figure shows that the maximum COP locates some biased point. Nevertheless, in the larger open region than 11.5% of opening, it obviously shows that COP is elevated with respect to close of expansion valve and Dh/DP is much larger than Dw_ =DP. In this aspect, it can be told that this real time control method helps a CO2 refrigeration system to avoid being operated with inadequately large expansion opening