The idea proposed in this paper is to control the HVAC equipment with predicting the heating/cooling loads and indoor conditions by computational simulation according to the target, such as energy consumption, energy cost, CO2 generation and indoor thermal comfort. The simulation inputs is given by the measurement results, e.g. weather conditions, indoor temperature and humidity on the spot. The developed system controls HVAC system by using the real-time simulation, and investigates the performance of this system.