OAA assists architects, mechanical engineers, and project development teams with evaluation and control of HVAC system noise in order to meet interior noise goals and exterior regulatory requirements. OAA is experienced in accurately predicting interior and exterior sound levels during a project’s design phase, offering the ability to consider this important aspect of design prior to construction, in order to avoid costly after-the-fact remediation that may be challenging or infeasible.
Control of interior background sound levels is one of the most important but least-appreciated aspects of acoustical design. High background sound levels hamper the ability to understand speech, interfere with music performances and recording, and can cause discomfort. For interior concerns, consultations involve prediction of interior HVAC sound levels based on manufacturers’ source data and ASHRAE algorithms, as well as comparison with project criteria. Where exceedances of criteria are predicted, OAA develops recommendations for noise control elements such as lined ductwork, dissipative silencers, barriers to duct breakout noise (e.g. heavy-gauge ductwork, duct lagging, duct enclosures, and/or special ceilings), and quieter equipment selections. Noise control elements are optimally selected for each air path. Noise transmitting from a mechanical room to an adjacent noise-sensitive space is also a frequent concern.
For exterior concerns, consultations involve prediction or modelling of exterior sound levels from rooftop equipment, louvers, and sound transmitting through enclosures or façades; comparison with project criteria based on regulatory limits for off-site sound emissions and comparisons with ambient sound levels to determine acoustical impact; and development of recommendations for noise control elements such as acoustical barriers.
HVAC Noise Control Projects
- Air-Cooled Chillers, James J. Flynn Elementary School, Perth Amboy, New Jersey
- Atkinson Hall Science Research Building, Cornell University, Ithaca, New York
- Air-Cooled Condensing Units, Morristown Medical Center, Morristown, New Jersey
- Rooftop HVAC Equipment, Millburn Middle School, Millburn, New Jersey
- Water-Cooled Chillers, Prudential, Newark, New Jersey
- Interior Air Handlers, Morristown High School Broadcast Studio, Morristown, New Jersey
- Plant Expansion, Chartwell Pharmaceuticals, Congers, New York
- VAV Boxes, Olin Chemistry Research Building, Cornell University, Ithaca, New York
Ostergaard Acoustical Associates assisted Dattner Architects, WSP USA, and the Metropolitan Transportation Authority (MTA) with the design of the new Hudson Yards Subway Station serving the No. 7 Subway Line. One of the significant challenges for the project was control of noise radiated from a unique installation where banks of air-cooled chillers were installed in the interior of a ventilation building, which is atypical for air-cooled chillers. The chillers draw air from 3rd-floor intake louvers, and discharge the air into a plenum on the 4th/5th floor where it transfers out of the ventilation building. Constructed above the ventilation building is a high-rise Class A office building, 55 Hudson Yards. Chiller air intake and exhaust louvers comprise about 2,300 ft2 of louver area immediately below the 6th-floor windows of the office building.
To meet the noise criterion agreed to between the MTA and the office building owners, significant chiller noise attenuation was needed. The design parameters for the project meant that the combined pressure drop of the air intake and discharge silencers could not exceed 0.30 inches w.c. At the intake side of the chillers, significant dimensional constraints limited the silencer depth to less than 2 feet.
OAA engineered a custom noise control solution with the strategy of short high-pressure-drop silencers on the air intake side, and tall low-pressure-drop silencers on the discharge side. OAA and the design team worked closely with the silencer manufacturer throughout the submittal, fabrication, and installation process to ensure successful chiller noise control. Post-installation measurements indicated that chiller sound levels were controlled below the project criterion by a comfortable margin.