Rooftop HVAC Unit Mega Duct Attenuator

Development of a new mid-rise residential tower resulted in a complaint about noise. Noise was transmitting from an existing hotel rooftop HVAC unit located one city block away. The City's daytime and nighttime noise ordinance required a ten-decibel reduction of noise. Initial recommendations for noise reduction and concomitant energy savings were rejected by the Owner as being too complex. Instead, the Owner accepted an alternative - a large, low-pressure-drop, custom-built, elbow duct attenuator. This was fabricated and installed on the outdoor-air-intake end of the unit. Complaints ceased. Comments and photographs will show design computations, specification, fabrication and installation of the silencer. Subsequent actions by the Owner for additional noise control and energy savings are of interest.