ASABE Technical Library - Abstract

Abstract. Variable frequency drives (VFDs) allow fans to operate at a lower frequency when their full capacity is not needed. At static pressures common in animal housing, this can increase fan efficiency. We wanted to know whether the increases in energy efficiency justify the increased costs of equipping the ventilation system with VFDs. We also wanted to know whether VFDs could improve fresh air distribution during cold weather by more evenly distributing where air is exhausted. Herein, we predict energy efficiency and cold-weather airflow distribution in a low profile cross-ventilated dairy barn for scenarios in which VFD-driven fans and single-speed fans are used for ventilation. Performance data from tests performed on a 57” Schaefer exhaust fan are used to predict the system‘s efficiency as a function of static pressure and frequency. A computational fluid dynamics (CFD) model is then used to simulate the cold-weather airflow distribution for both cases. The estimated energy savings resulting from equipping the example barn with VFDs pay for the system‘s additional cost in 3 to 6 years. The CFD model predicts both systems provide similar airflow patterns during cold weather. However, the impacts of VFDs on both air distribution and energy efficiency are site-specific. Most importantly, VFDs only save energy when the system is running at partial capacity, providing little benefit for systems that almost always run at full capacity.