VFD or Damper?
Industrial fan installation and applications are full of choices, big and small, immediate and long-term. One of the small choices that can make a big difference in the long term is whether to use a Damper or a Variable Frequency Drive (VFD) to control the capacity of your industrial fan. While some may choose both options depending on their applications, many fan users make an “either-or” decision.
In our experience, the VFD is more common, primarily because of the energy savings it can offer. But there are reasons to choose a damper too.
What is a Damper?
A fan damper is similar to air vents in your car. You can open or close louvers to adjust the air flow -increase by opening the damper and decrease by closing. The fan & motor speeds remain constant. There are (2) main types of dampers and they adjust fan capacity with different system effects:
- Inlet Vane Damper (VIV) – installed on the inlet of the fan and swirls the air in the same direction as the fan rotation. They are commonly modulated with electric or pneumatic actuators. This is the most efficient damper option. Power consumption can be reduced, though not as much as with a VFD.
- Outlet Damper – mounted on the outlet of the fan and simply “throttles” the air leaving the fan. This damper is the least efficient option, as it increases system pressure drop as the air flow decreases.
How About a VFD?
A VFD is a motor controller that can adjust the motor speed and thereby change the fan speed. This allows the fan user to adjust airflow by either decreasing or increasing the motor’s speed. Back to the car air vent analogy, using a VFD is the equivalent to you reaching over and changing the fan speed on your air conditioner rather than just opening or closing the air vent.
How to Decide Between a Damper and a VFD
A system rarely operates at constant conditions, and flexibility often matters to the system’s user. It’s critical to determine how important system flexibility and energy savings are to you before making a decision on a Damper or VFD. With that in mind, here are some key considerations:
- How many hours will the fan be in operation?
- What is the cost of power in your area?
- How finite can your system controls be?
- Dampers have lower up-front costs than VFD’s, but VFD’s can provide higher long-term savings in energy costs.
- VFD’s provide the most system flexibility.
- Outlet dampers may be a great option if cold-starting the fan is the only concern (when the air’s temperature at start-up is colder than the actual operating temperature).
- Dampers can be used to regulate and balance system pressure.
We find that many of our customers will use a VFD with motors above 50 horsepower, as the $$ savings from reduced power consumption outweigh the cost of purchasing a VFD. That being said, VFD’s are also used with smaller motors. It all depends on the application!
Hear it from the Application Engineer
Senior Application Engineer Fred Besasie provides an overview of considerations for VFD’s and dampers in this 2-minute video.
When you’re ready to start your project, reach out and connect with one of our application engineers to discuss the details of your specification.
Related Content on Industrial Fan Applications
There are many factors beyond fan controls to consider in every industrial fan application. We’ve seen it all. Here are two more articles that might be of interest as you think about your application:
- FAN SELECTION: HOW TO TELL US WHAT YOU NEED
- INLET BOX: DO YOU NEED ONE IN YOUR CENTRIFUGAL FAN APPLICATION?