To Affinity… and Beyond! Estimating VFD Power Draw From Motor Speed

Variable frequency drives (VFDs) are an energy-efficient method of matching system output to the load. Energy engineers often estimate the power draw of a VFD-driven system using the full load (100% speed) power draw and the estimated or actual operating speed. This article offers guidance on the equations to use when developing those calculations and aims to clarify the differences between the speed-to-power and flow-to-power exponent values.