A properly applied Variable Frequency Drive (VFD) will significantly reduce operating costs. This is particularly true for variable torque loads such as:

Fans
Blowers
Pumps

Blowers, for example, are often used with dampers to control air flow. These dampers may be operated either manually or automatically. When dampers are closed, 50% motor current will drop to approximately 60% of Full Load nameplate current. By utilizing a Variable Frequency Drive (VFD) in this application, current draw in the motor will be reduced 30% for every 10% drop in speed. The same motor operating from a Variable Frequency Drive (VFD) at 50% speed will draw approximately 20% of FLA.

An example application:

A 10 HP AC motor rated 90% efficient running across the line with the dampers operating between 50 – 70% for 2000 hours per year will require 11,996 KWH. If your KWH charge is $.08 per KWH, the cost to run this motor will be: $1,248.00 annually.

The same motor operating from an ASD between 50 – 70% speed for 2000 per year will require 4,676 KWH. Operating cost at the same KWH rate will be: $ 432.00 per year. This represents a savings of $ 816.00 per year and should be enough to pay for the investment into a drive and installation costs in the first 12 months of operation.

If the application operates more hours than in this example and/or the KWH charge is higher the savings will compound very fast.

: Reduce Energy Costs Up To 60% Using a Variable Frequency Drive

Another factor to consider is mechanical wear. Because the motor and blower in this application is running at a lower speed mechanical wear will be proportionally less. You should also expect less vibration and heat that may affect other equipment nearby.

Most VFD’s will accept a 4-20 Ma input signal for speed reference and control. Most pressure transducers and automatic controllers can be wired directly into the same control position as your automatic damper. (also 4 – 20 ma)

The same theory will apply to all variable torque loads. A variable torque load is one that the load on the motor shaft increases when speed increases, or decreases when the speed decreases.