The effect of deflectors on Air Diffusion Performance Index of adjustable diffusers: Cooling condition (RP-1546)

Abstract

Diffuser selection guidance listed in ASHRAE Handbook—Fundamentals (ASHRAE 2009b) includes Air Diffusion Performance Index values for horizontal high sidewall grills and ceiling linear slot diffusers. However, grills are adjustable at various angles, which generate different airflow patterns in a space and therefore might greatly affect Air Diffusion Performance Index values. Also, complaints of draft generated by ceiling slot diffusers are common because of inappropriate adjustment of diffuser deflectors. This study measures the Air Diffusion Performance Index values of three widely used adjustable diffusers—adjustable-blade grills, fixed-blade grills, and ceiling linear slot diffusers—at various deflector configurations in a test room with 25- and 50-W/m² (7.9- and 15.8-Btu/hr/ft²) cooling loads. The study explores how deflector adjustments affect diffusers, with performance represented by Air Diffusion Performance Index values. The results show that upward blade deflectors can increase Air Diffusion Performance Index values greatly for blade grills. In general, downward jets reduce Air Diffusion Performance Index values for each adjustable diffuser type operating at cooling conditions. A smoke test can assist in the adjustment of linear slot diffusers to create the desired ceiling-attached airflow patterns during commissioning.

Acknowledgments

The authors wish to thank Krueger, Metalaire, Nailor, Price, and Titus for their generous donation of diffusers.