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Industrial Fan Flow Control: The Hows and the Whys

By In Blog On October 20, 2020

Industrial fans hold court over a variety of industries and applications. Gas management, pressurized airflow and air exchange, and other important processes rely on a range of fans for movement. Whether you delve into mining, agriculture, or HVAC, you can be sure a centrifugal or axial fan system makes their presence known forcefully.

Most industrial fans within a system operate at a constant speed to maintain a fixed rate or velocity. Operators must preside over any fan system to regulate and control that airflow. Here’s a deep look into fan flow control methods and why changes in speed may be necessary.

Several Methods Control Fan Flow

Flow change is possible through various methods in a fan or system.

Pulley Change

One way to change fan volume is to alter fan speed via a pulley change. This method works when a fan is driven by a motor through a v-belt system. Pulley changes are quite simple but permanent, and should only occur if the fan is able to tolerate the air capacity change.

Fan speed will increase or decrease with a slight change in the drive pulley, the driven pulley, or sometimes both. Usually, a higher sized fan can be downsized when the drive pulley is exchanged for one with a smaller diameter.

Damper Controls

Certain fans contain damper controls at the inlet or outlet. When system resistance is added or removed in the form of a damper, air volume decreases or increases respectively. Damper controls allow operators to generate more or less air while a fan remains at a constant speed. However, dampers are not very energy efficient because that fan maintains a fixed power consumption as it generates less air.

Inlet Guide Vanes

Another way to provide variable airflow is with inlet guide vanes, or adjustable curved sections located near the fan inlet. Vanes help alter the angle at which air enters the inlet and meets the fan blades to increase or decrease speed. Guide vanes are more energy-efficient than dampers, especially for modest airflow changes.

Variable Speed Drives

Variable speed drivers, or VSD, provide great variability in speed control because they reduce fan speed according to flow requirements. As flow demands change, so too does power input, which makes VSDs one of the most energy-efficient options.

Unfortunately, VSDs can be a pricey upgrade and are not the most economical method when a system experiences only sporadic or infrequent speed variations. On the plus side, VSDs reduce part-load noise generation and reduce wear on components like bearing and belts.

Parallel and Series Operation

If expensive VSDs, inefficient dampers, or permanent pulley changes are out of the question, consider operation in series or parallel. Both methods use fan combinations to reach target airflow while fan system size or fan diameter remains unchanged.

  • Parallel operation involves more than two fans that blow side by side to double the flow. This method works best when fans operate in low resistance environments.
  • Series operation involves a pattern of multiple fans to create a push-pull arrangement. Two fans placed in a series increases static pressure capability of airflow.

When the use of other control methods is realistic, operators can equip series or parallel fans with dampers, VSDs, and inlet guide vanes to boost flexibility and reliability further.

Why Fan Flow Control is Necessary

Many industries design and install a fan system to operate at a constant speed most of the time. However, occasions arise that demand an operation adopts one or more fan flow controls. For example, a booming business means a new run of ductwork within a facility that requires additional airflow. Or, poor design means an oversized fan drains power and an operation must reduce flow without a complete system swap.

Compressor-Pump & Service, Inc., helps clients size the appropriate fan system right the first time. We can advise you with regard to the right industrial fans for your needs.

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