ABB ACS880-07, Hardware Manual

Page: 74 / 274

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:
Δ p
s
= (1.5…2) · p
d
where
p
d
= 0.5 · ρ · v
m
v
m
= q / A
c
Dynamic pressure p
d
Air density (kg/m
3
) ρ
Average air velocity in the exit duct(s) (m/s) v
m
Rated air flow of the drive (m
3
/s) q
Cross-sectional area of the exit duct(s) (m
2
) A
c
Example
The cabinet has 3 exit openings of 315 mm diameter. The rated air flow of the cabinet is
4650 m
3
/h =1.3 m
3
/s.
A
c
= 3 · 0.315 2 · π = 0.234 m 2
v
m
= 1.3/0.234 = 5.5 m/s
p
d
= 0.5 · ρ · v
m
2
= 0.5 · 1.1 · 5.5
2
= 17 Pa
The required pressure in the exit air duct is then, 1.5…2 · 17 Pa = 26…34 Pa, below the
pressure in the room.
74 Mechanical installation