The strategies of buildings energy management can be developed through energy audit, analysis and simulation. Currently, different end-users of CQU buildings such as heating, ventilating and air conditioning (HVAC) units, electrical appliances, etc do not take full advantage of local sub-tropical climatic conditions. Therefore, climate-responsive strategies need to be implemented in order to take full advantage of the positive climate attribute of sub-tropical climate regarding efficient energy management and conservation measures. This study is conducted on a three-story library building of CQU. HVAC systems were selected for practical operational energy conservation measures (ECM) to take advantages of hot and humid subtropical climate. A baseline energy consumption profile of the building is simulated using building energy simulation software called Energy Express (EE). The simulated results are then validated with energy audit and on-site metered data. The means to utilize environmental conditions to improve building energy efficiency is investigated. Variable air volume (VAV) system as an energy conservation option is investigated and compared with existing constant air volume (CAV) system. This study found that about 12% energy savings could be achieved by replacing CAV system with VAV system as an option for energy retrofitting, and hence recommended to CQU management for consideration.