Hitchings and Shull (1993), present a case study of noise reduction techniques used in a large laboratory building addition.
Great care was taken to reduce noise levels in the laboratory by proper fan selection and efficient ductwork design and sound traps. During start-up, the system operated very quietly and no problems were discovered. Startup occurred in early spring. A few months later, after ambient temperatures had increased and additional sensible heat-producing equipment had been added to the laboratories, a noise problem did occur. When all the fume hoods were closed and there was not enough airflow through the system to keep the internal temperatures at or below setpoint, the general exhaust valves would open, as they were supposed to, to stimulate more supply flow. When this occurred, a great deal of noise was produced by the general exhaust valve, which propagated backward through the duct and out the exhaust grille in the ceiling. This was objectionable enough to the researchers that they would leave a fume hood open to prevent it from occurring. When this was discovered, a sound trap was inserted in the ductwork between the exhaust grille and the general exhaust valve. This solved the problem completely and the researchers no longer leave a fume hood open to compensate.
