FAQ June 2000
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Can Duct Configurator model return or exhaust ductwork?
No. To model return or exhaust ductwork, use both the Ductulator and the Fitting Loss Calculator. The resultant static pressure can be used
on the fan tab as "SP through equipment and return."
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How can Duct Configurator model a plug fan in a plenum?
Refer to the help file on "plug fan."
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Can I get sound information?
No. The next release will include sound information.
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Must I end with a VAV box or diffuser?
Yes, Duct Configurator requires an end device at every outlet on the system.
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Why do some sections exceed my pre-set
maximum velocity?
There are several possibilities. Most commonly, exceeding the maximum occurs in a section that
leads to a VAV box or a diffuser. When creating a VAV box or diffuser using duct designer, enter the
inlet diameter. The diameter specified becomes the immediate upstream section’s diameter as well. With
the size of that section determined, the velocity is simply a result of the diameter and cfm. A similar
situation exists at the fan. The next section is the same size as the fan.
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How do I transition from rectangular to oval ductwork?
This is a two step process. You must first transition to round and then transition to oval. There is no direct transition to change shape
from rectangular to oval.
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Static regain is not downsizing my duct sections enough
resulting in very low velocities. What is going on?
Static regain attempts to maintain the same static pressure throughout the duct system by recovering static
pressure from velocity pressure. To do this, it slows the velocity down by keeping the duct sizes large.
We defined a minimum velocity setting in the .ini file that allows you to set the minimum velocity
Duct Designer will uses to determine when to downsize the section.
To change the 500 fpm default in the program you need to modify the duct_dsn.ini file.
Click start menu and type "duct_dsn.ini" to view the ini file.
Look for a section labeled "[velocity]"; if velocity is not there add it as shown.
e.g.
[velocity]
limit = 1500
This example sets the minimum velocity for static calculations to 1500 fpm. Change the "limit"
in the ini to provide greater flexibility in attaining your needed velocity requirements.
In version 3.0 or Duct32, there is an advanced features to set this number.
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Why after changing the minimum velocity, are my velocities still too low?
The reason is that when the program reaches the minimum setting, it has an associated actual (not nominal)
ductsize at that moment. For example, the Duct Designer sees that the 500fpm minimum has been reached,
and the duct size happens to be 5.2 inches in diameter. Since 5.2 inches is not a standard size of
ductwork, Duct Designer chooses the next LARGER duct size, which is 6 inches. The velocity will
then dip slightly below the 500fpm minimum.
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Why is my airflow increasing as I move away from the fan?
You have entered a diversity factor for a VAV system. At the fan, the airflow
will be less than the sum of airflow at the boxes. Size the sections leading out the boxes for the maximum peak airflow. Size the trunk
section only for the maximum block airflow.
Size sections going to the VAV boxes for the peak airflow.
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