Emerson Unidrive M700 Installation Manual page 31

Calculating the air-flow in a ventilated enclosure
The dimensions of the enclosure are required only for accommodating the equipment. The
equipment is cooled by the forced air flow.
Calculate the minimum required volume of ventilating air from:
3kP
V
-------------------------- -
=
T T
–
int ext
Where:
V
Air-flow in m
Maximum expected temperature in °C outside the enclosure
T
ext
T Maximum permissible temperature in °C inside the enclosure
int
Power in Watts dissipated by all heat sources in the enclosure
P
P
k
Ratio of ------ -
P
Where:
P is the air pressure at sea level
0
P
is the air pressure at the installation
I
Typically use a factor of 1.2 to 1.3, to allow also for pressure-drops in dirty air-filters.
Example
To calculate the size of an enclosure for the following:
• Three drives operating at the Normal Duty rating
• External EMC filter for each drive
• Braking resistors are to be mounted outside the enclosure
• Maximum ambient temperature inside the enclosure: 40 °C
• Maximum ambient temperature outside the enclosure: 30 °C
For example, dissipation of each drive: 101 W and dissipation of each external EMC filter: 6.9 W
(max).
Total dissipation: 3 x (101 + 6.9) = 323.7 W
Insert the following values:
T 40 °C
int
T
30 °C
ext
k 1.3
P
323.7 W
Then:
3 1.3
× ×
V
-------------------------------------- -
=
40 30
–
3
= 126.2 m /hr (74.5 ft
Unidrive M/HS Frame 3 and 4 Power Installation Guide
Issue Number: 3
3 3
per hour (1 m /hr = 0.59 ft
o
l
323.7
3 3
/min) (1 m
/ hr = 0.59 ft
3
/min)
3
/min)
31