ASHRAE Terminology

A Comprehensive Glossary of Terms for the Built Environment
ashrae.org/ashraeterms

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air, makeup

see makeup air.

down-discharge makeup air

makeup air delivered directly to the interior plenum of an exhaust hood such that it is introduced vertically downward, typically from the front edge of the hood. Sometimes this kind of makeup air is referred to as an air curtain.

internal discharge makeup air

makeup air delivered directly to the interior of an exhaust hood such that it is exhausted without entering the occupied space. Sometimes this kind of makeup air is called short-circuit makeup air.

makeup air

(1) dedicated replacement air. (2) air brought into a building from the outdoors to replace air that is exhausted. Makeup air may or may not be conditioned. (3) any combination of outdoor and transfer air intended to replace exhaust air and exfiltration. (4) in a cleanroom, air introduced to the secondary air system for ventilation, pressurization, and replacement of exhaust air. (5) in a laboratory or kitchen, outdoor air deliberately brought into the building from the outside and supplied to the vicinity of an exhaust hood to replace air, vapor, and contaminants being exhausted. Makeup air is generally filtered and fan forced, and it may be heated or cooled depending on the requirements of the application. Makeup air may be delivered through outlets integral to the exhaust hood or through outlets in the same room.

makeup air (dedicated replacement air)

outdoor air deliberately brought into the building from the outside and supplied to the vicinity of an exhaust hood to replace air, vapor, and contaminants being exhausted. Makeup air is generally filtered and fan-forced, and it may be heated or cooled depending on the requirements of the application. Makeup air may be delivered through outlets integral to the exhaust hood or through outlets in the same room.

makeup air unit

air-handling unit that provides 100% outdoor air to offset air that is exhausted and exfiltrated, often providing conditioning or treatment of the outdoor air.

net exhaust flow rate

the exhaust flow rate for a hood minus any internal discharge makeup airflow rate.

replacement air

outdoor air that is used to replace air removed from a building through an exhaust system. Replacement air may be derived from one or more of the following: makeup air, supply air, transfer air, and infiltration. However, the ultimate source of all replacement air is outdoor air. When replacement air exceeds exhaust, the result is exfiltration.