How we cut energy use with a variable frequency drive

A pump running directly off the mains always spins at full power — even when demand is half that. A variable frequency drive matches speed to actual demand. On a real project this cut annual energy use by 18%; here's the calculation behind those numbers.

Where the savings come from

For pumps and fans, power scales with the cube of speed: cutting speed by 20% cuts power by roughly half. Throttling with a damper or valve just dumps that energy — a drive instead spins the motor at exactly the speed needed. The difference shows up directly on the electricity meter.

How the project ran, and the result

On a group of 6 pumps we measured operating modes for two weeks, pulled the load profile, and fitted drives to three pumps. Soft-start turned out to be a bonus on top — hydraulic hammer disappeared, and pipeline leaks dropped. The installation paid for itself in 14 months.

A drive is an energy-saving tool, but without the right load profile it's just an expensive box — measure first, buy second.

Practical tips

• Before installing, pull a real 1–2 week load profile.
• Verify the savings against meter readings — don't settle for a theoretical calculation.
• Factor in the mechanical savings from soft-start (belts, bearings, piping).