Fans

Fans are the most common noise source in HVAC systems. A variety of fan types and arrangements make the reduction of noise problems a challenge. The fan type, low static and uniform flow intake and discharge requirements add to the level of difficulty for noise control. Since a fan’s primary purpose is to move air, aerodynamics becomes the major factor in noise control design.

Propeller Fans

Problem	Solution
Propeller Fans - Very low static capabilities - Low frequency noise for fans with a low number of blades	Proper selection of fit-the-system silencers instead of catalog silencers is required. The selection and application of the silencer is critical to maintain an extremely low pressure drop. The silencer should be set back from the fan in order to decrease the pressure drop.

Centrifugal Fans

Problem	Solution
Centrifugal Fans - Uneven flow profile for intake and discharge - Tonal noise - Radiated noise - Lateral thrust and uneven weight distribution when mounting	- Flow shaping silencers. The type, shape and size of the silencer doesn't depend only on the required insertion loss. Silencers with flow shaping internals help reduce pressure drop and provide uniform air distribution. EX casing silencers are designed with the acoustic media out of the airstream, resulting in noise reduction at no added pressure drop (compared to ductwork). - Tuned Silencers – Silencers designed to attenuate all bands, but also are specifically designed to attenuate a particular frequency. - Enclosures – If the fan is in a noise-sensitive space, full fan enclosures could be required. However, limited access to the fan for maintenance is a disadvantage of fan enclosures. - Inertia base with proper selection of isolators. It is important to perform a centre-of- gravity calculation and select the appropriate isolators for each location on the inertia base to avoid over- or under-loading isolators. Thrust restraints are also required to counteract the lateral forces due to torque and static. Projects: Power Station El Paso, One London Place, Gateway Arena, CBC Headquarters, Pickering Community Center, University of Toronto Power Plant, Queen’s University Library, Cape Breton Regional Hospital

Problem

Solution

Centrifugal Fans

- Uneven flow profile for intake and discharge
- Tonal noise
- Radiated noise
- Lateral thrust and uneven weight distribution when mounting

- Flow shaping silencers. The type, shape and size of the silencer doesn't depend only on the required insertion loss. Silencers with flow shaping internals help reduce pressure drop and provide uniform air distribution.
EX casing silencers are designed with the acoustic media out of the airstream, resulting in noise reduction at no added pressure drop (compared to ductwork).
- Tuned Silencers – Silencers designed to attenuate all bands, but also are specifically designed to attenuate a particular frequency.
- Enclosures – If the fan is in a noise-sensitive space, full fan enclosures could be required. However, limited access to the fan for maintenance is a disadvantage of fan enclosures.
- Inertia base with proper selection of isolators. It is important to perform a centre-of- gravity calculation and select the appropriate isolators for each location on the inertia base to avoid over- or under-loading isolators. Thrust restraints are also required to counteract the lateral forces due to torque and static.

Projects: Power Station El Paso, One London Place, Gateway Arena, CBC Headquarters, Pickering Community Center, University of Toronto Power Plant, Queen’s University Library, Cape Breton Regional Hospital

Axial Fans

Problem	Solution
Axial Fans - Tonal noise - Uneven flow profile for intake and discharge - Lateral thrust - Access for maintenance - Breakout noise through flexible connectors	- Tuned silencers – Silencers designed to attenuate all bands, but also are specifically designed to attenuate a particular frequency. - Flow shaping silencers – Inlet and discharge silencers mounted directly onto the fan to be designed for uniform air distribution and low pressure drop. These silencers are designed for minimal turbulence. - Thrust restraints are required to counteract the lateral forces due to static. - Fan rollouts offer a possible option for large axial fans that pose accessibility challenges. The fan rollouts enable the axial fans to be easily removed and maintained. - High Transmission Loss (HTL) flexible connectors. Projects: Motorola Semiconductor Facility, Charles Tupper Office Building, Chicago Tribune Office Building, Motorola Semiconductor Facility, NASA Clean Room, Goderich Ventilation Shaft, Pathology Building Northwestern University Silencer Sheet: SS-11

Problem

Solution

Axial Fans

- Tonal noise
- Uneven flow profile for intake and discharge
- Lateral thrust
- Access for maintenance
- Breakout noise through flexible connectors

- Tuned silencers – Silencers designed to attenuate all bands, but also are specifically designed to attenuate a particular frequency.

- Flow shaping silencers – Inlet and discharge silencers mounted directly onto the fan to be designed for uniform air distribution and low pressure drop. These silencers are designed for minimal turbulence.

- Thrust restraints are required to counteract the lateral forces due to static.

- Fan rollouts offer a possible option for large axial fans that pose accessibility challenges. The fan rollouts enable the axial fans to be easily removed and maintained.

- High Transmission Loss (HTL) flexible connectors.

Projects: Motorola Semiconductor Facility, Charles Tupper Office Building, Chicago Tribune Office Building, Motorola Semiconductor Facility, NASA Clean Room, Goderich Ventilation Shaft, Pathology Building Northwestern University

Silencer Sheet: SS-11