HVAC Fans and Blowers

HVAC fans and blowers are used to move air through heating, ventilating, and air conditioning (HVAC) systems. They are an integral part of the air handling systems that bring or draw fresh air into buildings. HVAC fans and blowers can be mounted to an exterior wall (ventilation unit) or above the ceiling (plenum fan), or used as part of a ducted system (duct fan). The fan spins or the blower turns by means of an electric motor, thus creating unidirectional air flow. Often, the air is pre-heated or cooled. Types of HVAC fans and blowers include vents or ventilation fans, plenum fans, duct fans, duct blowers, roof fans, exhaust fans, inline fans, tube axial fans, vane axial fans, and centrifugal blowers.

HVAC fans and blowers differ in terms of performance and drive options. Parameters include air flow rate, static pressure, and media temperature. Air flow rate is the rate at which air moves within or between HVAC zones. Static pressure is the pressure at which an equal amount of air is supplied to and exhausted from a space. Media temperature is expressed as a range. The diameter of the fan, or the diameter or maximum dimension of the blower outlet is also an important specification to consider when selecting HVAC fans and blowers. There are two drive options: direct drive and belt drive. 

There are two styles and three classes for HVAC fans and blowers. The two styles are forced draft and induced draft. Forced draft refers to the movement of air under pressure. Forced draft fans and blowers are so named because they "force" air to move. Induced draft refers to the movement of air by means of an induced partial vacuum. Induced draft fans and blowers "draw" air. The AMCA class for HVAC fans and blowers describes the device’s compliance with requirements from Air Movement and Control Association (AMCA). 

Design configuration is an important parameter to consider when specifying HVAC fans and blowers. There are three main choices: axial, bi-lobal or tri-lobal, and centrifugal. Axial fans include propeller vans, vane axial fans, and tube axial fans. With these designs, the fan blade circulates parallel to the air flow. Bi-lobal and tri-lobal fans consist of multiple co-rotating, serpentine shafts that mesh to move air and gases in a controlled manner. The shafts mesh so tightly that backflow is prevented.  Typically, bi-lobal fans and tri-lobal are used to recirculate gases in process equipment when environmental consistency is required. Centrifugal fans include products with many different blade configurations. HVAC fans and blowers that use other designs are also available.

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