Variable frequency drives are sold as energy savers, and they are — but only on the right loads. Knowing which is which keeps paybacks honest.
Fans and pumps: the jackpot
Centrifugal loads follow the affinity laws: shaft power falls with the cube of speed. Slowing a fan 20% cuts its power draw roughly half. If a damper or throttle valve is doing the regulating today, a drive usually pays for itself within a year or two of running hours.
Conveyors and mixers: the steady gains
Constant-torque loads save less dramatically, but drives still trim losses at partial load, soften starts that hammer gearing, and cut demand charges by removing across-the-line inrush.
Where savings evaporate
Loads that genuinely need full speed all shift — a hard-worked compressor, a saturated pump — save little. A drive there buys control and soft starting, which may still be worth it, but call it what it is.
Measure before and after
A clamp meter and a week of logging beat any brochure curve. Measure, retrofit the best candidate first, and let its numbers make the case for the rest of the plant.
