Air Outlet Duct On The Cabinet Roof (Option +C130); Calculating The Required Static Pressure Difference - ABB ACS880-07 Hardware Manual

74 Mechanical installation

Air outlet duct on the cabinet roof (option +C130)


The ventilation system must keep the static pressure in the air outlet duct sufficiently below
the pressure of the room where the drive is located in order that the cabinet fans can
produce the required air flow through the cabinet. Make sure that no dirty or moist air is
able to flow backward to the drive in any case, even during off-time or while servicing the
drive or the ventilation system.

Calculating the required static pressure difference

The required static pressure difference between the exit air duct and the drive installation
room can be calculated as follows:
p = (1.5...2) • p
s
where
p = 0.5 •
• v
d
m
v = q / A
m c
p
d Dynamic pressure
Air density (kg/m
v
m Average air velocity in the exit duct(s) (m/s)
q
Rated air flow of the drive (m
A
c Cross-sectional area of the exit duct(s) (m
Example
The cabinet has 3 exit openings of 315 mm diameter. The rated air flow of the cabinet is
3 3
4650 m /h =1.3 m /s.
2
A = 3 • 0.315 • / 4 = 0.234 m
c
v = q / A = 1.3 / 0.234 = 5.5 m/s
m c
2
p = 0.5 • • v = 0.5 • 1.1 • 5.5
d m
The required pressure in the exit air duct is then, 1.5...2 • 17 Pa = 26...34 Pa, below the
pressure in the room.
For more information, contact ABB.
d
2
3
)
3
/s)
2
2
= 17 Pa
2
)