This is presented in Fig. 8. The case which is presented in Fig. 8 is the same as the case of Table 2. Dh/DP Represents the ratio of increased enthalpy to the increase of pressure according to the expansion valve opening change ((h_(i+1)-h_i)/ (P_(i+1)-P_i)) and it can be regarded as a corresponding term of ∂h/∂P. In ideal cases, the COP should be maximized at the point where the ratio of ∆h/∆P to ∆(w/) ̇∆P is the same with present COP and below this expansion valve opening, additional work is much greater than the cooling capacity increase, resulting in lowering the COP. 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 ∆ w ̇/∆P . 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