The paper aims to investigate the technologies of low energy cooling that are compatible with existing buildings in order to reduce the energy consumption and peak demand associated with the cooling of institutional or commercial buildings in subtropical Queensland, Australia. The performance and effectiveness of a standard direct-expansion air-conditioning system are compared with those of a chilled ceiling radiant cooling system and a mixed-mode system that combines natural and mechanical ventilation within the building systems in a subtropical climate. The simulation results suggest that the chilled ceiling technique is preferable compared to the mixed- mode technique for efficient operation over the whole year and energy savings of 13-14% are achievable. An example of a building plan and materials is used to run the base case. DesignBuilder, an EnergyPlus based dynamic thermal simulation engine, is the simulation and visualization tool of the study.