This paper introduces the application of the TAS simulation support software to determine the energy performance in between a full mechanical ventilated building than that of a hybrid ventilated-- combined mechanical and naturally ventilated (atrium area to be naturally ventilated) building. A modeled three-storey commercial office building will be used as the main subject of this analysis. To determine the thermal comfort level of the central atrium, Parameters will be set in such a way that the full height windows will be 100% open. Results will be then tabularized to determine and analysis the output of the simulation. Recommendations will be then given based on the output performance of the building. In Tropics, it’s very difficult to achieve better thermal comfort in a naturally ventilated building. With the help of these simulation tools we can find whether natural ventilation is possible in this tropical climate in terms of thermal comfort, ventilation system and energy demand.