Example definitions:

air admittance valve a valve in a drainage system to permit the entrance of ventilating fresh air and to even out pressure differences.

airborne sound sound conveyed as pressure waves in air.

air brick, ventilating brick; a brick with regular round perforations from stretcher face to stretcher face, used to reduce the weight of walling construction and for ventilating cavity walls, basement spaces, etc.

air-change rate, ventilation rate; the specified number of times per hour that ventilating air in a room is completely
renewed and old air extracted, expressed as the hourly volume of air provided to a space divided by the volume of the
space.

air conditioning a mechanical installation system providing warmed, cooled, clean and otherwise treated air into the habitable spaces of a building; see also central air conditioning.

air-conditioning duct an air duct used in an air-conditioning installation.

air-conditioning unit, air-handling unit; a piece of mechanical services equipment for treating air and conveying clean air into a space or building.

air content the total amount of air in a substance, expressed as a percentage by volume; in concreting, it is the total volume of air voids per unit volume in vibrated concrete, expressed as a percentage.

air-detraining   admixture, air-detraining agent; in concretework, an admixture included in the concrete mix to
inhibit the inclusion of air.

air diffuser in air conditioning, an inlet grille which gives direction to supply air passing through it.

air-distribution system in air conditioning, an installation consisting of ducting and pumping plant for distributing
treated air to outlets.

air dried, air seasoned; timber having reached equilibrium with outdoor atmospheric humidity, specified as 12% moisture content.

air duct in air conditioning and mechanical ventilation, a long closed pipe or vessel of sheetmetal for conveying air
to its points of use; see also ventilation duct.

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