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Considerations
PKG-PRC002-EN8
Equipment Room Location and Orientation
Self-Contained Acoustical
Recommendations
Successful acoustical results are
dependent on many system design
factors.
Following are general acoustical
recommendations. For more information,
or if there is concern about a particular
installation, contact a professional
acoustical consultant.
Location and Orientation of the
Mechanical Equipment Room
Locate the equipment room adjacent to
stairwells, utility rooms, electrical closets,
and rest rooms if possible (See figure
below). This minimizes the acoustic
effects and risk of workmanship or
installation errors. Place the discharge
and return air ductwork over these less
acoustically sensitive areas, using vertical
or horizontal fresh air shafts. Consult code
requirements for fresh air and smoke
purge constraints.
Return Air Ductwork
Duct the return air into the mechanical
equipment room. Connect ductwork to
the unit if local code dictates. The return
air ductwork must have an elbow inside
the equipment room. This elbow will
reduce sound transmissions through the
return duct. Extend the ductwork from
the elbow far enough to block the “line of
sight” to the exterior of the equipment
room. Use a minimum ductwork length
of 15 feet to the equipment room
exterior. Line the duct with two-inch,
three-pound density insulation. Use
multiple, small return ducts for better
acoustical performance to the occupied
space.
Supply Air Ductwork
Insulate the supply air duct with two-inch,
three-pound density insulation. Extend
this lining at least 15 feet out from the
equipment room wall, keeping the duct
aspect ratio as small as possible.
Minimize large flat panels since they
transmit sound. In addition, small aspect
ratios will minimize potential “oil canning”
of the duct due to flow turbulence.
The flexible horizontal discharge plenum
option helps avoid complicated ductwork
transitions. Ductwork turning vanes
typically improve pressure drop but
degrade acoustical performance.
Recommended Maximum Air Velocities
The maximum recommended velocity
for the discharge air duct is 2,000 fpm.
The maximum recommended velocity
for the return air duct is 1,000 fpm. Limit
air velocities below these operating
points to minimize the risk of flow
turbulence that causes regenerated
noise. Using round supply duct and static
regain allows maximum discharge air
velocities up to 3,000 fpm. Lining round
supply duct also substantially lowers
frequency noise attenuation. However,
flow regenerated noise potential
increases dramatically at air velocities
over 3000 fpm.
Self-Contained