This paper presents the online optimal control strategies of the central chilling system in a super high-rise building in Hong Kong. The work presented aims at developing a package of optimal control strategies and evaluating their energy saving potentials and finally implementing these strategies in the building to enhance its energy efficiency. Based on testing the effects of interactions within the cooling water system and chilled water system on the system operation performance, the optimal control strategies for the cooling water system and variable speed pumps with different installations in the secondary chilled water system are developed. These strategies are tested and validated in a virtual environment representing the real building system and its central chilling system prior to site implementation. The implementation issues the online control strategies for practical application are also addressed.