ASHRAE Terminology

component of a centrifugal fan or pump consisting of simple flat blades backwardly inclined to match the velocity pattern of the fluid passing through the impeller wheel for high-efficiency operation. Impeller blade width and length affect flow rate and pressure or lift performance. See centrifugal fan, centrifugal pump.

a ducted centrifugal fan used in a heating, ventilating, and air-conditioning system. See also centrifugal fan, fan.

in-line duct fan with centrifugal blades which can develop static pressures higher than normal duct fans. Also identified as a tubular centrifugal fan.

fan in which the air enters the impeller axially and leaves it substantially in a radial direction. Fan rotor or wheel within a scroll-type casing (shroud) that includes supports for either belt drive or direct connection. Centrifugal-fan-types are as follows: forward curve, backwardly inclined (backward curved), airfoil, or radial blade design. Fans can be provided as single width, single inlet (SWSI) or double width, double inlet (DWDI) configurations and are limited to 16 predefined arrangement types based on discharge location and rotation.

controlled expansion part of the casing of a centrifugal fan that receives fluid forced outward from the impeller or diffuser and leads it to the discharge. Compare to fan shroud.

(volute, scroll), part of the casing of a centrifugal fan or compressor that receives fluid forced outward from the impeller or diffuser and leads it to the discharge. Compare to fan shroud.

there are two main categories of fans used in HVAC&R applications: centrifugal and axial fans. Centrifugal fans types include the following: forward curved (FC), backward curved or backward inclined (BI), airfoil (AF), and radial. Axial fan types include the following: propeller, vaneaxial, and tubeaxial.

inlet ring, impeller shroud, impeller rim annular plate, or conical ring on the air inlet side of a centrifugal fan to which the impeller blades are fixed.

(also known as impeller hub disc or impeller hub plate), disc rotating with the axle to which the impeller blades of a centrifugal fan are fixed.

(also referred to as an in-line fan) a centrifugal impeller located within a cylindrical or rectangular housing, discharging in an axial direction. Its performance is similar to that of a centrifugal blower except its capacity and pressure are lower due to the less efficient fan arrangement.

fan that moves air in the general direction of the axis about which it rotates, parallel to the shaft, and flow through the centrifugal fan wheel, impeller, or propeller is substantially radial. The fan is typically mounted in a round duct or tube to improve pressure characteristics and has vane-type straighteners to remove much of the swirl or spin of the air created by the fan wheel to improve fan efficiency. Fans can be either direct drive or belt driven.