Centrifugal fans according to the curvature of the blades

Centrifugal fans with forward curved blades

Fans with forward curved blades have blades curved in the direction of rotation of the fan impeller. They are particularly sensitive to particles and are normally only used for clean air flow, such as in air conditioning. Forward-curved fans are typically used in applications where the static pressure is too high for a bladed axial fan, or a smaller centrifugal fan size is required, or the noise characteristics of a backward-curved fan are inadequate for the space. They are able to provide a lower air flow with a higher increase in static pressure compared to a bladed axial fan. They are usually used in FCU (fan coil) units. Overall, they are less efficient than backward curved fans.

Centrifugal fans with backward curved blades

Fans with backward curved blades have blades curved against the direction of rotation of the fan impeller. Smaller fans may have backward-sloping blades that are straight rather than curved. Larger backward-curved fans have the blades whose backward curvature mimics the airfoil cross-section, but both designs provide good operational efficiency with relatively economical construction techniques. These types of fans are designed to handle gas flow with low to moderate particulate loads. They can be easily fitted with anti-wear protection, but some blade curvature can be prone to solids build-up. Backward-curved impellers are often heavier than their forward-curved equivalents because they run at higher speeds and require stronger construction.

Back-curved fans can have a high specific speed range, but are most commonly used for medium specific speed applications – high pressure, medium flow applications such as in air handling units.

Backward curved fans are more energy efficient than centrifugal blade and forward curved fans, so for high performance applications they can be a suitable alternative to cheaper centrifugal blade fans.

Centrifugal fans with straight blades

Centrifugal fans have impeller whose blades extend straight out from the center of the hub. Centrifugal blades impellers are often used on particle-laden gas streams because they are least susceptible to settling of solid particles on the blades, but often have a greater noise output. High speeds, low volumes, and high pressures are common in centrifugal blowers [pochvalná zmienka] and are often used in vacuum cleaners, pneumatic material handling systems, and similar processes.