In the experiment by Kim and Kim (2012), the gas-cooler effectiveness was varied from 80 to 100% and 96% COP compared to the exact optimal COP was obtained using the real time controller (inlet water temperature of evaporator: 27 C). When the gas-cooler effectiveness ranged from 60 to 80%, 93% of the maximum COP was obtained (inlet water temperature of evaporator: 25 C) and it is fairly acceptable performance.