VFD on Fans, Pumps or Blowers

Why use a VFD on Fans, Pumps or Blowers? First, visualize your production facility:

• How many fans are started and stopped using a starter.
• What about pumps and blowers?
• How many of those use a started to control stopping and starting?
• Are you able to control the speed or flow?

Biggest question (and most costly) is: Are you wasting money and energy?

These are just a few simple questions that should start you thinking about better application control, which most times leads to energy savings. A variable frequency drive (VFD) might be your answer.

Simple Math Proves Savings

Most pumps, fans and blower systems are powered by induction motors. The energy used by an industrial induction motor is a function of the speed it runs at. In an induction motor, the power used by the motor varies depending on the cubed value of the motor’s speed. If the motor’s speed is raised, energy consumption increases. If the motor’s speed is lowered, so is energy use.

When you use a starter to start that induction motor, the motor comes on at full rated speed. This creates an inrush of electricity as well as full wear and tear on the motor and the motor housing. VFDs have the ability to run motors at a percentage of rated speed and, with limits, even above rated speed if desired.

Now about that energy savings. If you use a VFD run a motor at 50% rated speed, you are reducing the energy it takes to run the motor at rated speed by nearly 88%. How did I get this you might ask? Take the .5 speed and cube it. That is .5 x .5 x .5 = .125 or 12.5%. This means at half speed you are only using 12.5% of the same energy at full speed: That’s an 88% reduction. It sound like a lot of math, but contact me and I can walk you through it if needed. We do a ton of VFD work so I am happy to help.

Yaskawa Electric has an awesome online tool called the Yaskawa Energy Savings Predictor for estimating your own energy savings. Plug in some parameters and see what you think.

Without a VFD on a fan, or pump or blower, there is no other way to reduce the speed to realize this kind of savings. On pumps you may have a control valve. This valve controls flow or pressure. This consumes the same amount of energy on any position as motor speed is at rated speed the entire time. Fans might use a 2-speed motor but those motors lack the capability to vary motor speed to keep within the application needs. A VFD allows you to take process inputs and better control your application needs on fans, pumps and blowers.

Dan Mahoney helps plant engineers and automation and controls planners in the Houston area for Innovative-IDM. He’s a member of the President’s Club and can be contacted at [email protected]