This study presents a new approach for enhancing building energy performance by integrating the energy audit and simulation using DesignBuilder software on a university building located in Alexandria, Egypt. The approach aims to evaluate the existing buildings' energy performance, quantify and analyze the gap between design predictions and actual energy performance, and improve energy performance. The findings reveal that the validation of the simulated building with the measured data proves the accuracy of the simulation. Lighting control saves 1.11% of electricity with a 0.92-y payback period. HVAC operating pattern achieves a substantial 20.8% annual natural gas consumption saving with 7.2 and 2.21 y payback period for the automated and manual systems, respectively with 2.5 tons CO₂ emission reduction. Using the optimal annual operating schedule saves annually 20.88% of the total cooling and heating energy and achieves 365 thermally comfortable days.