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Fan Efficiency and Volume Controls

Selecting the correct industrial fan for your pneumatic system is critical to success. The more complex the air system, the more difficult selecting the correct industrial fan becomes. Add in the variable of multiple operators on a given pneumatic conveying system, and it becomes apparent that a safety factor for the fan’s capability to generate sufficient airflow is preferred. So how is this accomplished?

There are generally three methods to control your industrial fan’s volume output. Each has its advantage, however when thinking in terms of pure energy efficiency, there is a clear pecking order.

The first and typically cheapest to implement is an outlet damper, actuated manually, electrically, or pneumatically. While this usually represents the lowest capital cost of air volume control, it is also least efficient.

The second method involves the use of a damper on the intake side of the industrial fan. This can be done directly on the intake opening with an internal or external variable inlet vane (VIV) designed to pre-spin the air in the direction of wheel rotation, or through the use of an inlet box where a damper is mounted to the intake of this box with vanes set to pre-spin the air similarly to the VIV. These can also be actuated manually, electrically, or pneumatically. While this method has greater capital cost as compared to the discharge damper, the advantages include better system control and lower energy costs.

The third method of volume control – operate the industrial fan motor with a variable frequency drive (VFD). With the cost of VFD’s becoming more reasonable, return on investment has improved. This method is the most energy efficient way to control your fan’s volume. It gives you full control of your fan’s potential.

To discuss which fan or volume control method is best suited for your application, contact Indventech at 888-864-4344 or email sales@indventech.com.

Posted on 2 Comments

2 Responses

  1. Pepper White says:

    Hello,

    I have been doing an analysis for a VFD retrofit on two VIV fans. The first has a static pressure requirement that is about 80% of the potential of the fan. I found that with the relatively limited turn-down on the speed of the fan, and with the VFD inefficiency added (94% assumed), the VIV approach is actually a little bit less power using than the VFD.

    In a second application, although the VIV operates between 45% and 73% open, the operating points are again close to the full speed fan curve, and the savings potential is small, with a very long payback period. Do you have any insights regarding this?

    Thank you,

    Pepper White, P.E.
    LCI Energy
    174 High Street, Suite 103
    Ipswich, MA 01938
    (978) 356-7767
    lcienrgy@tiac.net

  2. keenan says:

    Hello Pepper,
    The inlet damper creates added resistance/pressure loss simply by being in the airstream. This can be estimated based on the fan’s air velocity. Assuming your benchmark is a fully open damper, have you tested the fan’s performance with no damper? Are their any negative inlet/discharge conditions such as elbows closer than 8 duct diameters to inlet/outlet, discharge elbow directed opposite of wheel rotation, or steep sloped transitions, all of which have negative system effects to the fan (causes unpredictable performance)?

    Regarding fan curves, I would not place too much trust in them, but rather create your own. It is odd that your operating points are so close to the full speed curve when the damper is 45-73% open. What type of fan are you testing?

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