One of the most effective methods to reduce energy consumption in buildings is to install the advanced HVAC equipments and to control them properly. This paper describes the optimum HVAC control system through the developed data platform, BACFlex that the simulation is executed using BEMS data, the weather forecasting, etc. The concerned targets are CO2 generation, energy consumption, comfort and cost. The brief structure of the system is explained and an example applied to the school is introduced. The accumulation of expertise of the construction, the tuning of the simulation model, the operation in many usages of buildings may offer the simplified systems.