It’s a unique challenge for mechanical engineers to design and select the air distribution items. The selection and choice of air distribution equipment involves products efficiency to meet space requirements as well as architectural features which compliment the interior design in the modern HVAC system, the wrongly chosen air outlets lead to failure of the entire HVAC system.
The consideration while doing a perfect and competitive selection of air outlet are occupant comfort, energy conversation, air quality and the cost. It is the foremost purpose of this Air Distribution Handbooks and standards.
Grille: A covering for any area through which air passes.
Register: A grille equipped with a damper or control valve.
Diffuser: An outlet discharging supply air in various direction and planes.
Slotted Outlet: A long narrow air distribution outlet comprised of deflecting members; located in the ceiling, side wall or sill with an aspect ratio greater than 10. Designed to distribute supply air in varying direction and plans and arranged to promote mixing of primary air and secondary room air.
Return: An outlet for return or exhaust air.
Damper: A device used to control the volume of air passing through an outlet or inlet.
Aspect Ratio: Ration of the length to the volume of air passing through an outlet or inlet.
Free Area = Effective Area: Total minimum area of the opening in air outlet through which air can pass.
Throw: The horizontal or vertical axial distance an air stream travels after leaving an air outlet before the maximum stream velocity is reduced terminal velocity (e.g. 50, 100, 150 or 200 fpm) defined by ASHRAE standard 70.
Terminal Velocity: The maximum air stream velocity at the end of the throw.
Primary Air: The air coming directly from the outlet.
Secondary Air: The room air which is picked up and carried along by the primary air.
Total Air: Mixture of primary and secondary air.
Stratified Zone: A region in which room air velocity is less than 0.075 m/sec (15 fpm).
Draft: Undesired local cooling of a baby caused by low temperature and movement of air.
Isothermal Zone: Air jet with the same temperature as the surrounding air.
Non Isothermal Jet: Air jet with an initial temperature different from the surrounding air.
Jet Velocity = Face Velocity = Outlet Velocity: The average velocity of air passing from the outlet, measured in the plane of the opening.