IM 830-6
12 www.DaikinApplied.com
Duct System Considerations
Proper acoustics is often a design requirement for schools.
Most of the problems that are associated with HVAC generated
sound can be avoided by properly selecting and locating the
components of the system. There are some general do’s and
don’ts:
The following suggestions can reduce the amount of sound
that reaches the occupied room:
• Use flexible duct connections.
• Make the discharge duct the same size as the unit
discharge opening for the first five feet.
• Line the first 5 feet of the supply duct.
• Make two 90-degree turns in the supply and return ducts.
• Keep duct velocity low and follow good duct design
procedures.
• Mount and support the ductwork independent of the unit.
• Line the first five feet of the return duct.
• Locate the return air intake away from the unit discharge.
• Provide multiple discharges.
• Restrict use of high pressure drop flexible ducting.
• Size the outdoor air and return air ducts to handle 100%
of the total cfm to accommodate economizer or morning
warm-up operation.
NOTICE
If a supply air duct with improper duct work is placed too close to
the unit discharge, it will result in substantial noise. Avoid such
forms of connections when designing ductwork where sound
shows suggested
duct considerations per SMACNA and ASHRAE.
Sound control applies to the return side of the duct design
illustrates suggested
installation of return-air duct. Note the return air opening, and
the sizing and changes in direction of the ductwork.
illustrates suggested installation of outdoor air
ducting.
Figure 21: Discharge Air Duct Work
Flexible Boot
5 Feet
Same Size As Unit
Discharge
Acoustically Lined
(First 5 Feet from Unit)
Two 90-Degree Turns
Ductwork Sized
Based On Airflow
Ductwork Supported Independent Of Unit
Unit Ventilator Discharge
Figure 22: Intake/Return Air Duct Work
Acoustically Lined
(First 5 Feet from Unit)
Flexible Boot
Ductwork Supported Independent Of Unit
Two 90-DegreeTurns
5 Feet Same
Size As Unit
Return
Unit Ventilator Return