Case Study: Air Cooled Chillers with Rotary Helical (Screw) Compressors at Hospital with Impact on Patient Rooms, Residential Neighborhoods, and Open Park

摘要

Air cooled chiller with rotary (helical) screw compressors installed at a new hospital were producing disturbing tonal noise in patient rooms, an adjacent open park, and neighborhoods five to nine blocks away. The hospital received numerous complaints, and retained JEAcoustics to provide noise mitigation recommendations. The chiller produced a distinct tone measured at 117 Hz. The criterion developed was based upon perceived annoyance according to the Composite Noise Rating (CNR) analysis acceptability levels. It was determined that the tonality should be decreased by 5 to 8 dB in the 125 Hz third octave band within surrounding neighborhoods. Mitigation recommendations included: (a) attenuate radiated compressor noise by wrapping the compressors with an insulated limp mass noise barrier jacket, (b) attenuate compressor discharge noise by inserting pulse diffusers in the compressor discharges, (c) control the intake noise by providing acoustic louvers, (d) control discharge noise of both the fans and the condensers by providing discharge attenuators, and (e) reduce reflected sound from building surfaces (f) provide laminated 1/2" windows in patient rooms facing the chillers. The client elected to implement recommendations incrementally. After the implementation of the first two recommendations, noise complaints ceased. Sound level validation measurements were made. JEAcoustics found that ～ a 5 dB tonal reduction had been attained. The attenuation design, sound level measurements, and the effectiveness of the mitigation efforts will be discussed.