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WSHP-PRC001-EN 27
Duct Design for Noise Control
Proper acoustics are often a design
requirement. Most of the problems
that are associated with HVAC
generated sound can be
avoided by properly selecting
and locating the components
of the system. Acoustical
modeling should be used
to find the lowest cost
design to meet a
specific sound
requirement, however,
there are some general do’s
and don’ts that should be
observed.
Figure 34 shows a supply air duct that
is placed too close to the blower to
provide substantial noise attenuation.
It also, represents the effects on sound
that a short supply branch connected
to the discharge may produce. Avoid
these forms of connections when
designing ductwork where noise
attenuation is critical.
The following suggestions will reduce
the amount of sound that reaches the
ocupied space:
• Design the duct run
with two 90-degree
turns
• Line the first 5 feet of
the supply trunk
• Line elbows and tran-
sition pieces, as well
as a short distance
upstream and downstream of the
fittings
• Use flexible connections to iso-
late vibrations
• Provide multiple discharges
• Keep duct velocity low
See Figure 35 for a positive represen-
tation of supply duct work design for
noise attenuation on units over 1 1/2
tons.
Application
Considerations
Figure 35: Desired supply-air ducting
Figure 34: Improper supply-air ducting