WattMaster MG331-21-VAVCAV - Manual (Page 29)

Form: WM-OE511-RndDmpr-Sub-01A
Page 2 of 2
VAV System
Round Damper Sizing
Use a load program to determine the peak
load for each zone. These calculations will
be used in selecting the appropriate zone
damper sizes.
The WMVAV System utilizes a typical low
pressure duct design. To reduce noise
problems, duct pressures should not ex-
ceed 1” W.C.
Primary trunk ducts used with WMVAV sys-
tems should not be “undersized”. This is
especially true of “pressure dependent” sys-
tems. With pressure independent systems
this is not as critical. With larger trunk ducts,
it is easier to assure relatively constant
pressure to each Round Damper. Runs
should be as short as possible, and the
trunk duct system kept as symmetrical as
possible to facilitate system balancing.
Wherever possible, run the trunk ducts
above corridors and locate the Round
Dampers above corridors to reduce the
noise in the space and facilitate service of
the valves. Trunk ducts should be sized for
no more than 0.1” W.C. drop per 100 ft. of
duct, and a maximum duct velocity of 2000
FPM.
Round Damper Selection Data OE511-XX-VAV Pressure Independent
Round Damper
Round Damper Round Duct Size
(Area Ft
2
)
6”
(0.188)
8”
(0.338)
10”
(0.532)
12”
(0.769)
14”
(1.050)
16”
(1.375)
CFM @ 1” Velocity Pressure
(Air Flow Probe “K” Factor)
474 950 1417 2120 2908 3700
Velocity Through Round Damper
FPM
Airflow Through Round Damper - CFM
(
ΔP
S
inches W.C. w/ Air Damper Full Open)
500
94
(0.01)
169
(0.01)
266
(0.01)
385
(0.01)
525
(0.01)
687
(0.01)
750
141
(0.03)
254
(0.02)
399
(0.01)
577
(0.02)
788
(0.01)
1031
(0.01)
1000
188
(0.05)
338
(0.03)
532
(0.02)
769
(0.03)
1050
(0.02)
1375
(0.01)
1250
235
(0.07)
423
(0.04)
665
(0.03)
961
(0.04)
1313
(0.03)
1718
(0.02)
1500
282
(0.09)
507
(0.06)
798
(0.04)
1154
(0.05)
1575
0.04) 2062
(0.03)
1750
329
(0.12)
592
(0.08)
931
(0.06)
1346
(0.06)
1838
(0.05)
2405
(0.04)
2000
376
(0.15)
676
(0.10)
1064
(0.07)
1538
(0.07)
2100
(0.07)
2749
(0.05)
WattMaster reserves the right to change specifications without notice
With pressure independent systems it is possible to exceed this
rule by up to 50%. However it is advised that unless you are ex-
perienced with VAV duct design the 2000 FPM rule should be
used. Using the maximum acceptable velocity for a branch duct
(typically 1000-1500 FPM for minimal noise), find the smallest
damper that will deliver the required CFM as determined by the
load program.
Locate the branch velocity used in the duct design program in
the left hand column of the Round Damper Selection Data table.
Move across the table and find the damper, which will provide
the acceptable CFM to meet the zone airflow requirements.
Note:
Compare the Round Damper size selected against
the duct size to determine if the next size up or down
will provide acceptable performance without requir-
ing a transition fitting.
OE511-XX-VAV–Pressure
Independent Round Damper