Air diffusion devices
In this chapter the aerodynamic characteristics of different types of ATDs are discussed. The criteria normally applied for the selection of supply and extract devices are also outlined.
5.2 Air diffusion glossary In BS 4773  ATD is deﬁned as ‘a component of the installation that is designed to ensure the predetermined movement of air into or from a treated space, e.g. grille, diffuser, etc.’ From this statement, it is clear that on selecting an ATD for a particular application the aerodynamic as well as the geometric characteristics of the device are required. For an exhaust or extract ATD the aerodynamic characteristics usually imply knowing the total pressure loss caused by the insertion of the device in the duct opening and for a supply ATD they also imply knowing the envelope of the air jet. Given below are deﬁnitions of the basic terms used in this chapter to describe the
characteristics of ATDs.