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Glass &Windows Selection

AFAN is an air pump that creates a pressure difference and causes airflow. The impeller does work on the air, imparting to it both static and kinetic energy, which vary in proportion, depending on the fan type.

Fan efficiency ratings are based on ideal conditions; some fans are rated at more then 90% total efficiency. However, actual connections
often make it impossible to achieve ideal efficiencies in the field.RINCIPLES OF OPERATION

All fans produce pressure by altering the velocity vector of the flow. A fan produces pressure and/or flow because the rotating blades of the impeller impart kinetic energy to the air by changing its velocity. Velocity change is in the tangential and radial velocity components for centrifugal fans, and in the axial and tangential velocity components for axial flow fans

The centrifugal return fan pulls air from occupied building space through the return air ducts. The return fan has airfoil type blades which are the most efficient among all centrifugal fan blades. Some of this air is exhausted outside through the exhaust air damper, while a small amount of it (variable) continues through the air handling unit to mix with air drawn in from outdoors. This mixture of outside air and return air, before additional heating and cooling, is called mixed air

The mixed air is filtered before entering the supply fan. The airfoil type centrifugal supply fan pushes the air through the heating and cooling stages of the AHU. The air is then distributed through a system of ductwork to all areas of the

Centrifugal fan impellers produce pressure from (1) the centrifugal force created by rotating the air column contained between the blades and (2) the kinetic energy imparted to the air by virtue of its velocity leaving the impeller. This velocity is a combination of rotative velocity of the impeller and airspeed relative to the impeller. When the blades are inclined forward, these two velocities are cumulative; when backward, oppositional. Backward-curved blade fans are generally more efficient than forward-curved blade fans.

Axial flow fans produce pressure from the change in velocity passing through the impeller, with none being produced by centrifugal force. These fans are divided into three types: propeller, tube axial, and vaneaxial. Propeller fans, customarily used at or near free air delivery, usually have a small hub-to-tip ratio impeller mounted in an orifice plate or inlet ring. Tubeaxial fans usually have reduced tip clearance and operate at higher tip speeds, giving them a higher total pressure capability than the propeller fan. Vaneaxial fans are essentially tubeaxial fans with guide vanes and reduced running

Fan selection

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