Reducing electrical energy consumption of AHU fans through the integration of variable frequency drives

Variable frequency drives (VFD) enable control of the speed of three phase motors which allows the motor to be operated with variable current inputs. This technology can be used in Heating, Ventilation and Air Conditioning (HVAC) systems to lower fan operating speeds, reducing energy consumption. The client has expressed a need for a more effective means of control for the operation of their two air handling units which regulate airflow throughout their office building located on a brewing facility campus. Currently, the supply fans for both air handlers (AHUs) operate at full capacity, regardless of occupancy of the building. The implementation of Variable Frequency Drives (VFDs) on these supply fans was explored due to the client's need for lower operating cost for the HVAC system serving the building studied by automating the Air Handler control. Using industry simulation and estimating software, a VFD schedule was developed to determine the capacity for operational cost savings for these two rooftop units, based on occupancy of the building. During weekends and non-business hours during the week, the power to the supply fans was modeled at lower percentages of the full operational capacity. The results of this analysis show that the implementation of VFDs on these two air handling units can reduce operational HVAC costs by 18%.