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contributed by :Rouhea
submitted June 9, 2003
How do I install a
duct fan to operate most efficiently?
(principles of effective ventilation)
Many
growers own fans powerful enough to move air of a city
block in Manhattan, but has failed to install it
properly, causing greater pressure reduction. This extra
pressure drop is called the system effect or system
dissipation, and can cause the fan to produce a smaller
volume of air than indicated in the fan diagram.
The following factors must be considered in
order to avoid system dissipation:
At the
Inlet
The distance to the nearest wall must be more than
0.75 the inlet's diameter.
The inlet duct's cross section must not be greater
than 112% or less than 92% of the fan inlet.
The inlet duct's length must be at least 1 x the
duct diameter.
The inlet duct must no have any obstacles to the air
flow (dampers, branching or similar).
At
the outlet
The angle at the reduction of the duct cross-section
must be less than 15 degrees
The angle at the enlargement of the duct
cross-section must be less than 7 degrees
A straight length of at least 3x duct diameter is
required after a duct fan.
Avoid 90 degree bends (use 45 degree)
Bends must be shaped so that they follow the air
stream after the fan.
If the connections are
different from this, there could be a greater pressure
reduction.
Circular duct fans for example, are
propulsive, pushing the air. And should be installed so
that the long duct is after the fan itself. |