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Centrifugal Fans vs. Axial Fans

fans

The two main kinds of fan systems, centrifugal and axial, each offer different benefits, efficiency levels, and costs—so which one is right for you? Keep reading for an overview of both fan systems, including common applications. 

Centrifugal Fans

Centrifugal fans change the air direction twice as the air moves through the fan, meaning the air turns into the wheel, then turns again into the ductwork or plenum. Sometimes called a “blower,” these fans usually have an involute type housing around the wheel or impeller. 
Centrifugal fan systems are very cost-effective when it comes to ducted systems and are widely used in industrial and power generation applications. In comparison to an axial design, a centrifugal fan: 

  • Has a greater range of static pressure capabilities (from moderate low to high static pressure)
  • Is more energy efficient over greater ranges 
  • Is more durable and resistant to corrosive, abrasive, and heavy dust-laden environments
  • Can be easily armored with wear resistant materials
  • Can be designed so that it has a non-overloading horsepower curve
  • Is well-suited for operation in ductwork systems 
  • Can be designed with self-cleaning characteristics

There’s a variety of impeller types that can go into your centrifugal fan system. 
Forward curve (FC) impeller blades are commonly found in most residential and light commercial HVAC equipment. FC designs produce the most performance for a given size footprint.  They’re built for low to medium static applications, and are considered the most budget friendly—but least efficient—impeller blade option. 
Radial blade (RB) designs, albeit not very efficient, are rugged and dependable and well suited for harsh environments.  
Radial tip (RT) impellers are normally used in heavy dust-laden applications where high volumetric flow rates with moderate pressures are needed.  
Backward inclined (BI) impellers are used in both clean and dirty environments. This design normally has a non-overloading horsepower curve. It lends itself well to being armored for a wear-prone environment and is more efficient than a RB or RT design.  
Backward curved (BC) fan blades are very efficient, built to last, and quiet. These features, of course, make them more on the expensive side of things. The BC design is universal and can be applied in clean and wear-prone environments and well-suited in forced or induced draft applications.  
Airfoil (AF) impellers are shaped like airplane wings, and perform similarly to backward curved fan blades—although they’re a little more efficient, a little quieter, and a little more expensive to build. When evaluating initial cost as well as power saved through the life of the equipment, these designs will most often be the most commercially attractive option. AF designs are not suited for moisture-laden or dust-laden environments. 

Axial Fans

Axial fan systems don’t change the direction of the air, so everything flows in and out in the same direction or basically straight-line flow. These types of fan systems can provide extremely high volumetric flow rates flow at low to very low static pressures. You’ll most likely see these kinds of systems in free-blow unit heaters, and in condenser sections in rooftops or split systems. In power generation applications, they are used as booster fans when additional air pollution control equipment has to be installed to meet more stringent regulations.
In comparison to a centrifugal design, an axial design: (1) is normally more energy efficient, (2) produces higher dynamic or velocity pressures, (3) per capacity requirement consumes less power, (4) can move extremely large volumetric flowrates and (5) is typically smaller, lighter and less expensive.  
With axial fan systems, your blade type options include tube axial, vane axial, and propeller. 
Tube axial fan blades consist of propeller-shaped blades that are mounted in a tube. These blades are generally built for low pressure ductwork. 
Similar to tube axial blades, vane axial blades have air straightening vanes added in front or behind the propeller blades. This design is used on a large scale in power plants as booster fans where a small increase in pressure is needed for an extremely large volumetric flow rate.  Variable pitch vane axial designs are highly efficient over a broad range of operation as the pitch of the blade can be altered in flight. 
Propeller fan blades are mounted in a flat frame, and are usually built for installation in walls, open ceilings, or floor mounts. 
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