ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4pNSb1. Quiet unlined HVAC ductwork: Using active silencing to obtain NC-35 in buildings without fibrous materials.

Steve Wise

Lawrence J. Gelin

Kirk G. Burlage

Susan H. Dineen

DIGISONIX, 8401 Murphy Dr., Middleton, WI 53562

Fan noise in HVAC ducts has traditionally been attenuated with fibrous internal duct liner or with passive silencers constructed with porous fill material. Now, with active noise control, it is possible to cancel the loudest frequencies in the fan noise spectrum using inert components on the duct-microphones and loudspeakers. Proper selection of fan type, optimal duct design, and appropriate active noise control system configuration can achieve acceptable noise levels in all octave bands in the sensitive building spaces. Many recent examples of actual installations are given, including systems on air handlers up to 25 000 cfm capacity. Systems are applied, not only the central station air handlers, but also to secondary fans such as those used in fan-powered VAV boxes. Application considerations such as duct design and energy efficiency will be noted in this paper along with the specific room acoustical requirements and system performance.