ASHRAE Terminology

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

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diffuser

(1) circular, square, rectangular, or linear air-distribution outlet, generally located in the ceiling, and composed of deflecting members discharging supply air in various directions and planes and arranged to promote mixing of primary air with secondary. (2) duct of increasing area following the outlet of a rotary blower so that the reduced velocity of the fluid will convert some of the kinetic energy into pressure energy.