ASHRAE Terminology

a diffuser, grille, register, or transfer grille used for controlling air patterns or air distribution or for preventing line of sight through an opening while allowing airflow through. See air terminal device or diffuser.

(1) distribution of the air in a space, called the treated space, in a manner to satisfy certain specified conditions such as air change rate, pressure, cleanliness, temperature, humidity, air velocity, and noise level, in a specified zone within this treated space, which is called the occupied zone. It is usually achieved by means of air terminal devices which form the common boundaries between the treated space and the air-distribution system. (2) the introduction of air into a building space for the purpose of providing acceptable velocity and temperature distribution in the occupied zone.

there are three main categories of components: air-terminal devices (ATDs), complementary accessories to air terminal devices, fixing accessories for air-terminal devices.

1) the flow of air through the building envelope caused by a specified pressure difference, a measure of airtightness, cfm at fixed pressure (m3/s at fixed pressure). 2) undesirable or unwanted leakage of air from within a component within an air-distribution system that could include such items as ducts, air terminal devices, and AHUs.

any device (e.g., grille, register, diffuser) placed in an opening to a room, through which controlled air enters or leaves. Component of the air-distribution system which has the purpose of achieving the predetermined movement of air into or from a treated space.

modular air-terminal device designed to diffuse air to the treated space from a pressurized plenum through holes or slots in the ceiling surface or the supporting framework. Also see air terminal device.

the effective area of an air terminal device equal to the measured airflow rate divided by the velocity reading of a particular instrument used in a prescribed manner.

product of minimum height (h) and minimum width (b) of the front opening of a sand trap louver assembly with the louver blades removed. Also see core area of an air terminal device.

area of an air terminal device located within a convex closed surface of minimum area, inside of which are all openings of the air terminal device through which the air can pass.

air terminal device intended to be installed above a natural ventilation exhaust duct with the aim (by creating negative pressure and depending on wind speed) of avoiding reverse flow and increasing flow rate. It may or may not have moving parts.

air terminal device that is designed for thermally controlled ventilation (e.g., displacement flow applications). Also see air terminal device.

see manual damper.

nominal value of dimensions of the prepared opening (duct) into which the air terminal device is to be fitted.

(also called plenum box and plenum chamber) (1) a compartment or chamber, to which one or more ducts are connected, that forms a part of the air-distribution system and that is not used for occupancy or storage. A plenum often is formed in part or in total by portions of the building. (2) an air compartment that is attached to, or is an integral part of, a forced-air furnace which is designed to either distribute the heated air after it leaves the heat exchanger in the case of a supply plenum or to collect air that enters the return inlet in the case of a return plenum. (3) component forming an interface between a ductwork and one or more air terminal devices, by virtue of its design or by the inclusion of accessories, it can also be used to equalize the pressure/velocity across the air terminal device.

(of an air jet in mixing air diffusion), maximum distance (dv) between two vertical planes tangent to a specified isovel and perpendicular to a plane through the center of the core of an air jet. There may be two different spreads, not always equal: one for the left side, the other for the right side (considered when looking at the treated space from the supply air terminal device).