Where are VFDs appropriate for blowers?

Variable-frequency drives (VFDs) are adjustable-speed ac-motor controls that increase or decrease speed on non-explosion proof motors. Where their inclusion in designs are justified, they boost design performance and efficiency, minimize maintenance requirements, and extend blower life. They allow closed loop feedback, system monitoring and real time control of the blower motor.

First some background on the most common iteration — where VFDs pair with ac motors: Recall that induction motors are the most common of all motors used in large industrial blowers. With induction motors, energy consumption is a function of running rpm cubed — which means there’s significant energy savings for even small speed adjustments. The catch is that blower motors must be sized to satisfy maximum-load conditions — even if such situations are relatively rare. So for average operating conditions, blowers are oversized — and run inefficiently unless there’s some type of speed control to optimize flow to operating settings.

Here, VFDs can reduce and increase induction-motor speed as needed to satisfy application demands even while maximizing energy efficiency. That’s a capability that helps induction-motor-based blowers outperform comparable single-speed-motor or two-speed-motor arrangements. What’s more, VFD-based blower control can optimize overall design functions — especially in process industries. Plus VFDs can provide dynamic braking and replace motor-starter functions. This is important because motors otherwise come online full rated speed — which in turn spurs current inrush and physical wear on the motor.

In addition, many VFDs for pairing with blower motors accept 4-to-20 mA, 0-to-5 Vdc, or 0-to-10 Vdc inputs for integrated automation installations. Some accept three-phase or single-phase inputs to drive three-phase motor-blower assemblies. VFDs with digital readouts (reporting Hz or rpm) and NEMA-rated keypad enclosures are available — and the latter can in some cases mount dozens of feet from the controls. (As covered in other AMETEK literature, installations that separate controller and motor by 50 ft or more necessitate a line reactor on the load side.

There are parameters for sizing VFDs to pair with blower motors — such as allowable speed. Required rpm values for optimal performance (to get target pressure and air flow from the design’s blower) is listed in manufacturer literature. Required rpm must stay within the connected blower motor’s speed capacity. That said, VFDs can (where allowable and required) run motors at a above rated rpm.

Motor

Allowable turndown

Standard

3,600 rpm to 1,800 rpm

High efficiency

3,600 rpm to 900 rpm

Inverter motor

3,600 rpm to 360 rpm

One note that relates to inverter-duty motors: Turn-down (the ability to reduce air-flow rate) exceeding 10:1 is uncommon on regenerative blowers. So for applications with speeds exceeding 3,600 rpm, consult with the blower manufacturer for horsepower sizing.

Speedup is not recommended on Regenerative blowers due to the increasing horsepower demand per the fan laws.

Part number

Model number

Description

IV101AE58

551529

115/1 • Up to 0.5 hp • DR068-DR303

IV102AE58

551530

230/1 • Up to 0.5 hp • DR068-DR303

IV101AL58

551531

115/1 • 0.75 to 1.0 hp • DR353-DR404

IV102AL58

551532

230/1 or 3 • 0.75 to 1.0 hp • DR353-DR404

IV103AL72

551533

460/3 • 0.75 to 1.0 hp • DR353-DR404

IV102AS58

551534

230/1 or 3 • 1.5 to 2.0 hp • DR454-DR505

IV103AS72

551535

460/3 • 1.5 to 2 hp DR454-DR505

IV102K58

551536

230/1 or 3 • 2.5 to 3 hp • DR505-DR555

IV103K72

551537

460/3 • 2.5 to 3.0 hp • DR505-DR555

IV102D58

551538

230/1 or 3 • 3.5 to 5 hp • DR555-DR808D

IV103D72

551539

460/3 • 3.5 to 5 hp DR555 to DR808D

IV152AY58

551540

230/3 • 5.5 to 7.5 hp • DR808-DR858

IV152AY72

551541

460/3 5.5 to 7.5 hp • DR808 – DR858

IV152BB58

551542

230/3 • 8 to 10 hp • DR858-DR909

IV153BB72

551543

460/3 • 8 to 10 hp • DR858-DR909

IV152BC58

551544

230/3 • 10.5 to 15 hp • DR909

IV153BC72

551545

460/3 • 10.5 to 15 hp • DR909

IV152BH58

551546

230/3 • 15.5 to 20 hp • DR9 • DR14BH

IV153BH72

551547

460/3 • 15.5 to 20 hp • DR9 • DR14BH

IV152BP58

551548

230/3 • 20.5 to 30 hp • DR13 • DR14

IV153BP72

551549

460/3 • 20.5 to 30 hp • DR13 • DR14

IV152BQ58

551550

230/3 • 30.5 to 40 hp • DR15

IV153BQ72

551551

460/3 • 30.5 to 40 hp • DR15

IV153ED72

551552

460/3 • 50.5 to 60 hp • DR15