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ACOUSTICAL CONSIDERATIONS
In order to minimize sound transmitted to the space, please con-
form to the following recommendations (see Fig. 1):
Location
•
Avoid locating the unit above sound-sensitive areas.
Instead, locate the unit above restrooms, storage areas,
corridors, or other noise-tolerant areas.
•
Avoid mounting the unit in the middle of large roof
expanses between vertical supports. This will minimize the
phenomenon known as roof bounce.
•
Install the units close to vertical roof supports (columns or
load bearing walls).
•
Locate the units at least 25 ft away from critical areas. If
this is not possible, the ductwork and ceiling structure
should be acoustically treated.
•
Consider the use of vibration isolators or an acoustic curb.
Ductwork
•
Utilize flexible connectors between the unit and the supply
and return ducts.
•
Supply and return air main trunk ducts should be located
over hallways and/or public areas.
•
Provide trailing edge turning vanes in ductwork elbows
and tees to reduce air turbulence.
•
Make the ductwork as stiff as possible.
VIBRATION
ISOLATORS
IN ROOF
CURB
FLEXIBLE
CONNECTORS
SUPPLY AND
RETURN
INTAKE
PLENUM
SUPPLY AND RETURN
DUCTS LINED WITH
ACOUSTICAL DUCT LINER
Fig. 1 — Acoustical Considerations
•
Use round duct wherever possible because it is less noisy.
•
Seal all penetrations around ductwork entering the space.
•
Make sure that ceiling and wall contractors do not attach
hangers or supports to ductwork.
•
Provide as smooth and gradual transition as possible when
connecting the rooftop unit discharge to the supply duct.
•
If a ceiling plenum return is utilized, provide a return
elbow or tee to eliminate line-of-sight noise to the space.
Face the entrance of the return duct away from other
adjacent units.
Acoustic Insulation
•
Provide acoustic interior lining for first 20 ft of supply and
return duct or until the first elbow is encountered. The
elbow prevents line-of-sight transmission in the supply
and return ducts.
•
Install a double layer of 2-in. low density quilted fiberglass
acoustical pad with a
top of the roof deck before building insulation and roofing
installation occur. Place the material inside the curb and
for 4 to 8 ft beyond the unit perimeter, dependent upon unit
size (larger units require a wider apron outside the curb).
Openings in the pad should only be large enough for the
supply and return ducts. An alternate approach is to use
two layers of gypsum board with staggered seams in addi-
tion to the acoustical pad.
SUPPLY
DISCHARGE
FAN
PLENUM
COMPRESSOR/
CONDENSING
SECTION
ROUND DUCT CONTROLS
RUMBLE BEST
4
1
/
-in. barium-loaded vinyl facing on
8
ALL ROOF
PENETRATIONS
SHOULD BE
SEALED
AIR TIGHT
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