Centrifugal fans are the most commonly used type of fan in industrial HVAC systems. Compared to axial fans, centrifugal fans are generally cheaper and also offer simpler construction.
Backward-curved blades curve opposite of the fan wheel's rotation. Backward-inclined blades that have straight blades are generally used in smaller blowers while larger blowers often incorporate backward-inclined blades that are curved with a shape similar to the cross section of an airfoil. Both blade designs allow good operating efficiency and are designed to handle gas streams with low to moderate particulate loadings.
These fans can be fitted with wear protection but depending on the type of blade curvature, "solid buildup" can occur. Backward curved wheels are often heavier than corresponding forward-curved equivalents, as they run at higher speeds and require stronger construction. While more expensive than forward-curved fans initially, they are more efficient and respond better to changes in static pressure.
Plenum Fans are designed for air handling and pressurized plenum applications. The main benefits of plenum fans include compact sizes, flexibility to supply multiple air take-offs, and economical price. The design of plenum fans save energy and also reduce low frequency tones that are difficult to attenuate, improving sound quality. Titan Air generally uses belt driven plenum fans, but direct drive is also available.