GB.SILVERSK.170901
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3.2 Adjusting the Duct System
and air diffusers
In order to prevent the fans from consuming more power
than necessary, it is important to keep the pressure drop in
the system at the lowest possible level. It is also important
that duct systems and air diffusers are correctly commis-
sioned to provide the comfort expected.
When commissioning air diffusers and the duct systems
for the SILVER C, it is appropriate to follow the proportion-
ality method.
This means that the ratio between the airflows in branch
ducts remains constant even if you change the airflow in
the main ducts. The same ratio applies to the air diffusers
in the installation.
3.2.1 Adjustment Sequence
The system should be adjusted in the following order:
1. Adjust of the air diffusers in each branch duct.
2. Adjust the branch ducts.
3. Adjust the main ducts.
3.2.2 Commissioning procedure
1. Set all the air diffusers and dampers to the fully open
position.
2. Calculate the quotient between the airflow reading and
the design airflow of all the air diffusers, branch ducts
and main ducts. The air diffuser in every branch that
has the lowest quotient should be fully open. Use this
air diffuser as an INDEX AIR DIFFUSER. The same applies
to branch dampers and main dampers.
When you’ve finished commissioning, one air diffuser
in every branch, one branch damper and one main
damper should consequently be fully open.
Example on how to make an adjustment
– Start adjusting duct branch B, since this one has the
highest quotient.
– The last air device, B3, has the lowest quotient and
should be fully open.
Adjust the other air devices, B1 and B2, so that these will
have the same quotientas air device B3 (see item 5 above).
– Now adjust the air devices in branch duct C. Air device
C4 should be fully open; throttle the others to the same
quotient.
– Adjust the air devices in branch duct A. The index air
device here is air device A3, which means that you first
throttle air device A4 (the reference device) to device A3:s
quotient. Then adjust the others to the same quotient as
air device A4.
– Throttle branch damper B to the same quotient as branch
damper A, throttle branch damper C to the same quotient
as branch damper A.
Check that all dampers have the same quotient.
When commissioning has been completed, 3 air devices
and one branch damper should stand fully open to obtain
the lowest possible pressure in the system.
qp = design airflow (l/s)
qm = flow reading (l/s)
qm
K (Quotient) =
qp
3. Start adjusting the main duct that has the highest
quotient and the branch duct in the main duct that has
the highest quotient. Starting from this point enables
you to then "press" the air in front of you toward the
sections of the system that have the least air.
4. Adjust the last air diffuser on the duct branch so that
it will have the same quotient as the index air diffuser.
This air diffuser becomes the REFERENCE AIR DIFFUSER.
The last air diffuser on the branch is often the one that
has the lowest quotient and this air diffuser should be
open. In this case, the index air diffuser and the refer-
ence air diffuser will be one and the same.
5. Throttle the other air diffusers in the branch to the same
quotient as the reference device.
NOTE! The quotient in the reference terminal will
change every time another air diffuser is throttled, so
in practice the quotient for the reference air diffuser
can be set slightly higher. The reference device must be
measured in between each air diffuser throttled.
6. Go to the branch that had the next highest quotient
and adjust the air diffusers there, etc.
NOTE! All branch dampers should be fully open until all
air diffusers have been adjusted.
7. Throttle the branch damper that had the highest quo-
tient to the same quotient as the branch that had the
lowest quotient.
NOTE! Keep in mind that the index damper changes
quotient; proceed as described in item 5.
8. When all branches have been commissioned, throttle
the main dampers in the same manner.
See also Adjustment example below.
