Air-Handling-Unit Discharge Air Temperature Reset Based on Outdoor Air Temperature and Cooling Energy Performance in an Office Building

In many office buildings, an air-handling unit (AHU) in a variable air volume (VAV) system is operated using discharge air temperature (DAT) simply fixed at a particular set point. However, this simply fixed control causes a variety of inefficiencies related to cooling energy. Therefore, this study compares the cooling energy consumption of the fixed-control strategy, which fixes the AHU DAT at a specific temperature, and the cooling energy consumption of an AHU DAT set point reset strategy based on the outdoor air (OA) temperature, which proportionally controls the AHU DAT according to the change of the OA temperature. Commercially available software was used to compare the AHU DAT control methods of fixed control and the AHU DAT set point reset strategies. The comparison results show that the effect of reducing the total cooling energy consumption in summer (June to August) is negligible; however, in spring (March to May) and autumn (September to November), it was found to be significant compared with the single-fixed-control method. Therefore, if a method of proportionally controlling the AHU DAT is implemented, as in the case of the AHU DAT set point reset based on the OA temperature, it could be an advanced control scheme to improve energy efficiency, especially by reducing the energy consumption of the chiller, which accounts for the highest proportion of the total cooling energy consumption.