Rounded Corners

Terminal Units

In order to distribute heating and cooling and provide individual occupant control, fan-powered boxes are used in HVAC system design. These terminal units are typically placed right above occupied spaces to improve energy consumption and air distribution. Unfortunately, all terminal units create noise. As a result, noise control needs to be considered.

Duct-borne Noise

Problem Solution

Duct-borne Noise

Duct-borne noise - Noise traveling through the ductwork and out of the diffusers and return grills is a problem that should be addressed at the design stage. However, the location of the silencer solution, obscure duct transitions, and precise calculation of the amount of silencing actually required are common problems that designers run into every day.

This process always needs to start with a systems analysis that includes transmission loss calculations, aerodynamic analysis and a survey of the project specific requirements (space, IAQ, pressure drop, and cost). A project-specific solution can then be selected and applied.

Projects: IBM Headquarters Office Building, Hawaii NC-20 Studio

Space

Problem Solution

Space

In addition to space restrictions, shorter duct runs pose the problem of increased system effects and potentially generated noise.

Fit-the-system silencers taking the shape of the ductwork enable designers to achieve the insertion loss required across all bands in the limited duct space available, while keeping system effects to a minimum.

ASHRAE recommends 3-5 duct diameters on either side of a silencer; however, this amount of space is rarely available. Fit-the-system silencers such as Elbow Silencers help overcome space restrictions that most consultants face on a regular basis

Radiated Noise

Problem Solution

Radiated Noise

Noise can radiate off the unit walls, through the ceiling tile and into the occupied space.

Location – Fan-powered boxes should not be located over the occupied space.

Lagging of the fanned powered box casing is another option 

Pressure Drop

Problem Solution

Pressure Drop

Maintaining a low pressure drop is important in order to avoid affecting the distribution of air.

Flow shaping silencers. The type, shape and size of the silencer do not only depend on the required insertion loss. Silencers with flow shaping internals help minimize pressure drop and provide uniform air distribution for fan intake and discharge.

EX casing silencers are designed with the acoustic media out of the airstream, resulting in noise reduction at limited to no added pressure drop (compared to ductwork).