Using a Variable Frequency Drive to Improve your System Performance

A Variable Frequency Drive (middle bottom) as part of a recirculating heat system

What is a Variable Frequency Drive?

Variable Frequency Drives (often known by their initials: VFDs) convert a fixed-frequency supply voltage (60 Hz in North America) to a continuously variable frequency. By controlling the frequency of the voltage supplied to an AC motor, we can control its rotational speed and minimize stress. A VFD can control two main elements of a 3-phase induction motor: its speed and torque.

Motor-driven systems are typically designed to operate at peak load. This leads to energy inefficiencies when a system is running at a reduced load over time. A variable frequency drive gives an operator the ability to adjust the speed of the motor, matching the motor output and load requirements, thus resulting in energy savings.
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VFDs are used for two main reasons:

• To improve the efficiency of motor-driven equipment by matching speed and output to the application’s requirements
• To allow accurate and continuous process control over a wide range of speeds

Why use a VFD with your blower motor?

The rate of rotation for an industrial blower’s blades is driven by its motor speed; even a small reduction in speed can result in significant energy savings.
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The blower affinity laws govern the relationship between rotation speed, flow, and power. The laws state that:

• Volumetric airflow is proportional to speed
• Blower pressure increases with the square of speed
• Power consumption increases with the cube of speed

Therefore, in a practical application where speed has been reduced to 75 percent of the design speed:

• Volumetric airflow decreases by 75 percent
• Outlet pressure decreases by 56 percent
• The input power requirement decreases by 42 percent

​Besides saving energy, VFDs are also used to:

• Control pressure and flow without the use of a separate controller
• Lower maintenance costs
• Extend the life of your blower by reducing wear
• Eliminate the need for:
  • Throttling valves
  • Dampers
  • Soft starters
• Protect equipment from excessive torque

​Our systems are available with Variable Frequency Drives to help reduce operating costs and ensure your system is sized perfectly to your production needs. Contact us today to find out how we can help solve your application problem.

Originally published: 1/20/2014