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26 RT-PRC031-EN
Applications Considerations
will help reduce sound transmission.
The ASHRAE publication "A Practical
Guide to Noise and Vibration Control
for HVAC Systems" also provides
valuable information.
There are several other sources of
unit sound, i.e., supply fan, exhaust/
return fans, and aerodynamic noise
generated at the duct fittings. Refer
to the ASHRAE Applications
Handbook, Chapter 47, 2003 edition
for guidelines for minimizing the
generation of aerodynamic noise
associated with duct fittings. A good
source of information on general
acoustical considerations for air
handlers is the 2000 ASHRAE Journal
article titled, "Controlling Noise from
Large Rooftop Units".
The Trane Acoustic Program (TAP)
allows complete modeling of air
handler acoustical installation
parameters. The software models
airborne sound from supply and
return ducts, as well as duct breakout
and roof transmission sound, so that
the designer can identify potential
sound problems and make design
alterations before equipment
installation. Output of the program
shows the resulting NC (or RC) level
for any point in the occupied space.
TAP is also capable of modeling the
effect of outdoor sound on the
surrounding area. This program is
available from Trane's Customer
Direct Service Network
TM
(C.D.S.),
ask your local Trane representative
for additional information on this
program.
Clearance Requirements
The recommended clearances
identified in Figure 31, p. 85 should
be maintained to assure adequate
service capability, maximum capacity
and peak operating efficiency. If the
clearances shown are not possible on
a particular job, consider the
following:
• Do the clearances available allow
for major service work such as
changing coils?
• Do the clearances available allow
for proper outside air intake and
exhaust air removal?
• If screening around the unit is
being used, is there a possibility
of air recirculation from the
exhaust to the outside air intake?
Actual clearances which appear
inadequate should be reviewed with
a local Trane sales engineer.
When two or more units are to be
placed side by side, the distance
between the units should be
increased to 150 percent of the
recommended single unit clearance.
The units should also be staggered,
see Figure 15, p. 26, for two reasons:
1
To reduce span deflection if more
than one unit is placed on a single
span. Reducing deflection
discourages sound transmission.
2
To assure proper diffusion of exhaust
air before contact with the outside air
intake of adjacent unit.
Figure 15. Unit Placement
Outdoor
Air Intake
Outdoor
Air Intake
Exhaust
Air
Outdoor
Air Intake
Outdoor
Air Intake
Exhaust
Air