The Main Hall Building (MHB) at Shinawatra University was designed with the purpose of energy conservation in a tropical zone. However, energy consumption in this building is relatively high when considering the limited number of occupants and the efficiency of the air conditioning system. This study aims to audit the energy consumption of the air conditioning system in order to determine its energy performance, and to identify an efficient way of managing the system. Recommendations for the energy conservation of the air conditioning system are proposed, and the energy cost savings related to the recommended schemes are determined. The air conditioning system takes the highest share of energy consumption at approximately 70%. The rest is consumed by lighting and other systems at 12% and 18%, respectively. It was found that the chiller plant is operating inefficiently, because the central air conditioning system was not designed to operate at low cooling load demand. Energy conservation using the existing air conditioning system can be achieved by changing to the smaller (190-ton) chiller during office hours. Many air conditioned areas in the MHB, which are not fully utilized, should be closed down to decrease the load of the chiller and reduce the energy use of the air handling units (AHUs) and fan coil units (FCUs). A multiple pump operation in the chiller plant system is also recommended. By following the recommended management schemes for an air conditioning system, the university can save approximately 2.26 million baht annually. This finding illustrates the importance of good energy management in buildings.