Compliance with the ANSI standard requires projects to limit maximum allowable background noise levels from HVAC equipment based on section 4.3 of the ANSI standard and provide after construction measurements to verify compliance. Projects will have a bet

Compliance with the ANSI standard requires projects to limit maximum allowable background noise levels from HVAC equipment based on section 4.3 of the ANSI standard and provide after construction measurements to verify compliance. Projects will have a better chance of meeting the measurement requirements by following these practices. (See the ANSI standard—and in particular Annex B—for full details.) 

• Do not use unducted systems.
• Provide grilles and diffusers with a catalog Noise Criteria (NC) rating of 18 or less.
• Trunk ducts airflow velocity must not exceed 4.1 m/s.
• Install duct silencers inside the air-handling unit or in supply and return ducts.
• Design and install all duct work to have a low static pressure loss in accordance with SMACNA for HVAC System Duct Design.
• Locate all rotating equipment and equipment with static pressure control dampers at least 10 feet from classrooms.
• Use airfoil-shaped blades with centrifugal fans, in most cases.
• Ductwork serving more than one core learning space may need sound attenuators or sound-absorbing duct lining.
• Do not locate VAV boxes or fan-powered boxes over core learning spaces.