Centrifugal blowers, or fans, are among the most efficient and versatile pieces of air moving equipment. The scroll housing in a centrifugal fan accelerates the air and changes the direction of the airflow twice, a full 90 degree, before leaving the housing. Centrifugal blowers are quiet and reliable and are made to operate in a variety of environments and applications. Here are some basic definitions and guidelines to consider for selecting the right centrifugal blower for your system's needs.
Centrifugal Fan Blade Types
Centrifugal fans come in four basic fan types, each with its own specific purpose.
- Radial These are high-pressure fans with medium airflow. Radial-bladed fans are best for industrial applications where there is dust, or in environments where there is gas or moisture in the air.
- Forward Curve These are medium pressure, high airflow fans that can be used in both clean air, ventilating and exhaust applications.
- Backward Curve These are high-pressure, high flow, high efficiency fans. Power reduces as flow increases over the most efficient area of the system.
- Airfoil These are the highest efficiency fans, best in clean air applications.
To choose the appropriate blower, you'll need to know how much pressure is required to reach the desired airflow to move air through the ducting and any filters, dampers or other obstructions in your ventilation system. If you have a lengthy, complicated duct system, you'll of course need a lot more power. Consider the impact of filters on the airflow too as this will also impact the pressure and power needed.
Direct Drive is more typical on smaller blowers and generally offers lower cost, fewer components to assemble, greater efficiency (no drive losses), reduced maintenance (no separate bearings or belts) and greater reliability.
Belt Drive offers greater flexibility in matching airflow requirements when equipped with a variable pitch motor pulley and is typical of larger blowers. When equipped with a variable frequency drive (three-phase blowers), direct drive blowers can offer the flexibility of belt drive blowers.