Active noise cancellation in HVAC ducts

Modern heating, ventilation and air conditioning (HVAC) systems usually consists of a centralized air conditioning unit like a chiller plant, a series of long ducts which transport the processed air and an indoor unit to control the air flow to the room. Noise produced by the centralized air treatment units as well as due to flow of air in the duct is annoying and has been shown to produce fatigue. Several passive noise cancellation approaches have been attempted to reduce this noise levels. However, these passive noise cancellation approaches are not effective for low frequency noise mitigation. Active noise control, which works on the principle of destructive superposition of sound has recently evolved as an effective candidate for noise cancellation in the low frequency region. An attempt has been made in this thesis to consider active noise cancellation in a duct as a fluid dynamics problem and model the same using such techniques. Active noise cancellation in a duct has been studied from a fluid dynamic perspective and the results obtained are promising. In addition, we have successfully implemented an active noise control system in a duct and noticeable noise reduction has been observed.