ASHRAE Terminology

accessories intended to permit access into ducts, they are positioned in proximity to all those internal parts which require inspection and/or maintenance, such as fire dampers.

device, either electrically, pneumatically, or hydraulically operated, that acts as a motor to change the position of movable devices such as valves or dampers.

duct and dampers arrangement with an automatic control system that together allow a cooling system to supply outdoor air to reduce or eliminate the need for mechanical cooling during mild or cold weather.

(1) air-operated device that is used primarily for opening or closing pneumatic valves and dampers. (2) device that converts compressed air into mechanical force. (3) pneumatic operator, a final control device that assumes a position as directed by an input pressure signal.

adjusting airflow rates through air distribution system devices, such as fans and diffusers, by manually adjusting the position of dampers, splitter vanes, extractors, etc., or by using automatic control devices, such as constant-air-volume or variable-air-volume (VAV) boxes.

(1) an air-distribution assembly consisting of inlet duct connection(s) and outlet duct connection(s) whose purpose fulfills (either manually or automatically) one or more of the following functions: controls the rate of the airflow, controls the velocity or pressure and/or temperature of the air, mixes primary streams of different temperatures or humidities, or mixes within the device primary air with air from the treated space. (2) an air terminal unit may be composed of automatic or manual dampers, filters valves, heating or cooling coils, sound attenuation, nozzles, or fan assemblies. See also diffuser terminal.

device to control volume and flow in air distribution. See also damper.

the ratio of path pressure drop, including fully open control damper pressure drop, to the pressure drop across the fully open damper at design flow.

device which, when mounted in a duct or opening, permits the flow of air in one direction only. Can be gravity (counter weighted) or power operated.

adjustable blade device to control airflow.

(1) counterweighted damper set so that variations in chimney barometric pressure will cause the damper to open or close gradually to maintain a constant draft directly upstream of the damper. (2) mechanically balanced damper that rotates from changes in pressure within breeching to bleed air into the breeching to maintain a steady draft.

in an air-handling system, a sliding damper.

(1) damper consisting of a plate turning on a diametral axis inside a duct. (2) pair of flaps hinged to a common diametrical spindle and permitting flow in one direction only. (3) two flaps in \"V\" arrangement.

a pipe or duct, usually controlled by valve or damper, for conveying a fluid around an element of a system.

device to protect air openings in fire-rated ceiling assemblies that operates to interrupt airflow automatically in the event of fire in order to restrict passage of heat and flame.

factory-assembled fan consisting of one or several centrifugal wheels connected to a motor and enclosed in a housing. A back-draft damper can be provided.

device that receives a signal from a controller and acts on the process plant to vary its operating condition in accordance with the information received. In HVAC & R systems, controlled devices typically are valves, dampers, and motors.

element inserted into an air-distribution system or element of an air-distribution system permitting modification of the air resistance of the system and consequently changing the airflow rate or shutting off the airflow.

device that provides the necessary force to position a damper.

device to maintain constant downstream static pressure or volume flow.

total amount of the air in cubic feet per minute (litres per second) drawn through the casing and a fully closed damper/valve into the airstream of an exhaust terminal unit at a given outlet pressure.

interface between the fan and the remainder of the system at a plane perpendicular to the airstream where it enters or leaves the fan. Appurtenances such as inlet boxes, inlet vanes, inlet cones, silencers, screens, rain hoods, dampers, and discharge cones may be included as part of the fan between the inlet and outlet boundaries.

in air-handling units, the section containing the filters and the outside air/return air dampers and mixing plenum.

device that interrupts airflow automatically through part of an air system to restrict passage of flame. Installed in a fire-rated wall or floor and closes automatically in the event of fire to maintain the integrity of the fire-rated separation.

an electrical or mechanical device in the flue outlet or in the inlet of or upstream of the draft control device of an individual, automatically operated, fossil-fuel-fired appliance that is designed to automatically open the flue outlet during appliance operation and to automatically close the flue outlet when the appliance is in a standby condition.

isolation damper with a blade which is withdrawn from the duct area when the damper is fully open.

two or more slotted slides in parallel arrangement and adjustable against each other.

diffuser with the features of an air terminal. Air is modulated by outlet or inlet dampers.

sectorized blades.

devices that isolate HVAC zones so that they can be operated independently of one another. Also, a device, such as a service valve, that allows maintenance of a portion of a system. Isolation devices include, but are not limited to, separate systems, isolation dampers/valves, and controls providing shutoff at terminal boxes.

device that can be used to manually adjust the airflow rate by manual operation. Also see damper, valve.

device that can be used to shut off the flow by manual operation. Also see damper and valve.

see manual damper.

a modulating damper or set of dampers used to control the outdoor airflow to the system in excess of minimum ventilation outdoor air for free cooling (airside economizer). Also called economizer outdoor air damper. May also serve to provide the minimum outside airflow control.

a damper in parallel with the maximum outdoor air damper to provide the minimum outdoor air required for ventilation.

damper having two or more blades or leaves.

a number of shutters in opposed blade or parallel arrangement.

device that allows air to flow only in a predetermined direction. See backdraft damper.

combination grille and damper assembly over an air opening. See air outlet.

the flap centrally mounted or at one end (sometimes one or a combination of this damper is used as diverting element).

an approved opening protection device designed to resist the passage of air or smoke that meets the requirements of UL Standard 555S-1983, Leakage Rated Dampers for Use in Smoke Control Systems. A combination fire and smoke damper should also meet the requirements of UL Standard 555-1990, Fire Dampers.

(1) external static pressure loss for forced-air systems using packaged air-handling equipment, the static pressure loss resulting from airflow through the supply and return ductwork and other elements external to the packaged air-handling unit. Compare to internal static pressure loss and total static pressure loss. (2) internal static pressure loss for forced-air systems, the static pressure loss resulting from airflow through the internal elements of the packaged air-handling unit. These internal elements may include such items as filters, coils, dampers, mixing sections, etc. Compare to internal static pressure loss and total static pressure loss. (3) total static pressure loss for forced-air systems, the sum of the external static pressure loss and the internal static pressure loss. See internal static pressure loss and external static pressure loss. The term is not applicable to an individual fan or a fan located within a builtup air-handling unit. Fans are rated by the term fan total static pressure, which is not the same as fan total pressure. Compare to fan total pressure.

amount of air in ft³/min (L/s at standard conditions) escaping from the terminal at a given inlet pressure with only the outlet(s) blocked and with the damper/valve fully opened.

amount of air in ft³/min (L/s at standard conditions) passing through a fully closed damper/valve at a given inlet pressure.

see terminal damper leakage and terminal casing leakage.

air in cubic feet per minute (liters per second) leaking from a terminal unit at a given inlet pressure with the outlets and inlets blocked and with the damper/valve fully opened.

air in cubic feet per minute (liters per second) leaking through a fully closed damper/valve of a supply/exhaust terminal unit at a given inlet/discharge pressure.

a systematic process or service applied to heating, ventilating, and air-conditioning (HVAC) systems and other environmental systems to achieve and document air and hydronic flow rates. The adjustment of fluid flow rates through distribution systems by manually adjusting the position of dampers, valves, etc., or by using automatic control devices to control the position of dampers, actuators, valves, etc.

a device intended for installation in the venting system of an individual, automatically operated, fossil-fuel-fired appliance in the outlet or downstream of the appliance draft control device, which is designed to automatically open the venting system when the appliance is in operation and to automatically close off the venting system when the appliance is in a standby or shutdown condition.

device mounted in a duct or opening used to vary the volume of air flowing through.