An energy saving air conditioning system is disclosed which provides different air conditioning modes, including a closed-loop mode, an open-loop mode, and a partial-loop mode, for controlling the environment in a high-density apparatus room. The energy saving air conditioning system uses a cloud operating center to monitor the temperature and the moisture inside and outside the high-density apparatus room. The cloud operating system dynamically selects the air conditioning mode in such a manner that energy can be saved and the environment in the high-density apparatus room can be optimally managed.