Variable Air Volume (VAV) unit system is one of the commonly used forced-air heating and cooling systems in typical office buildings. Literally, it adjusts the supply airflow from the central Air Handling Unit (AHU) to meet the heating and cooling load of the building, while theAHU Supply Air Temperature (SAT) is usually fixed. This AHU SAT has significant impacts on the overall VAV system energy performance. In this study, the detailed analysis of the impact of AHU SAT in the conventional VAV system was performed in the typical office building prototype under Korean climatic condition using the whole-building energy simulation software platform, EnergyPlus version 7.1. Three different AHU SATs were investigated in this study: AHU SAT set-point of 13.9°C, 15.6°C and 17.2°C. It was observed that increasing AHU SAT raised the fan energy, while reducing the heating and cooling energy. Due to the fact that the amount of heating and cooling energy reduction was larger than that of the fan energy increase, the total HVAC energy consumption slight decreased with the higher SAT.