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VAV-PRC003-EN 39
Acoustics are tricky to define for
specific jobsites. To provide an
acoustical overview of a typical office
system with mineral glass fiber
dropped ceiling, ARI standard 885-98
has generated the transfer functions in
Table 11.
Sound power data was collected in
accordance with ARI Standard 880.
Applying the transfer function for
sound reduction due to office
furnishings, materials, etc. generated
the NC data which follows. This is a
reference document only provided to
address general acoustical issues.
What you will find is that the sound in
the occupied spaces generated by the
VariTrac dampers is minimal when
compared to the main HVAC unit
sound generation.
Acoustics
Some general ideas to minimize
acoustical issues:
• pay close attention to location of the
HVAC unit. This will typically set the
overall acoustical quality of your job.
• locate VariTrac dampers outside the
occupied space.
• internally lined ductwork can be used to
reduce the discharge sound generated
by the HVAC unit.
• install flex duct with minimal sagging,
and turns.
• locate balancing dampers as far from
the diffuser as possible to limit airborne
noise.
Note: VariTrac dampers do not carry the
ARI seal.
Table 11. Acoustical transfer functions
Table 12. Radiated sound data
NC Based on 885-98 Mineral Tile
Size Radiated NC Size
6 in. 33 470
8 in. 26 840
10 in. 25 1310
12 in. 26 1885
14 in. 29 2140
16 in. 21 2515
NC based on maximum rated airflow
conditions.
ARI 885-98 Discharge Transfer
Function Assumptions
Octave Band
234567
Small Box -24 -28 -39 -53 -59 -40
(<300 cfm)
Medium Box -27 -29 240 -51 -53 -39
(<300–700 cfm)
Large Box -29 -30 -41 -51 -52 -39
(>700 cfm)
Note: Add to terminal unit sound power to
determine discharge sound pressure in the space.
ARI 885-98 Radiated Transfer
Function Assumptions
Octave Band
234567
Type 2 Mineral -18 -19 -20 -26 -31 -36
Fiber Insulation