DA-88-03-1 -- Throw: The Air Distribution Quantifier PDF

The ability of an HVAC system to provide an acceptable degree of thermal comfort to the occupants of a building is determined by a number of factors. These include the quality of the supplied air, the control system employed, and the distribution of the supply air to the space. The most difficult parameter to quantify is the air distribution within the space.

The desire to predict the resultant room air currents has spawned a number of research projects during the past 30 years. These projects have resulted in standardized tests, equations, and guidelines, which encompass the room geometry, air quantities, type of diffuser employed, and the resulting air patterns and temperature distributions within the space. Essential to this analysis is a performance parameter of the supply air diffuser known as the diffuser "throw."

ASHRAE Fundamentals (ASHRAE 1985) provides a table that correlates the throw of a diffuser with ADYI, or Air Diffusion Performance Index. Using this table, a design engineer can determine the performance range of a selected diffuser, in terms of ADPI, which is related to predicted occupant comfort. Accurate throw data, therefore, is essential to the selection of diffusers in occupied spaces.

Modern computer-based technology now allows for accurate, repeatable, and easily accomplished throw measurement, both in the laboratory and in finished spaces. This technology a/lows for specification of, and verification of, throw values for air diffusers. Application of this technology allows for the design of spaces with optimum air diffusion and the resulting high comfort levels necessary for optimum productivity.

Units: Dual