Engineering Guide CDA3000
7-5
7 System installation
DE
EN
1
2
3
4
5
6
7
A
The factor f [m³K/Wh] is dependent on the altitude above sea level at
which the fan is operated (see Tabelle 7.1). This takes into account the
fact that the air pressure - and thus the air density - decreases as the alti-
tude increases and the fan consequently discharges less and less heat to
the outside while the volumetric flow remains constant.
Example: The fan is to be installed in a switch cabinet at an altitude of
80 m above sea level, having a power loss of 600 Watts. The temperature
values are T
i
= +40° and T
u
= +20°C. Application of these values in for-
mula (2) produces:
Therefore a filter fan with a delivery rate of at least 93 m/h is required.
The filter fans should generally be selected somewhat larger than calcu-
lated, since the operational side of the filter mat becomes increasingly
clogged with dirt and the heat discharge is thereby impaired. For this rea-
son the heat emission via the switch cabinet surface should also be
ignored when calculating the necessary volumetric flow of the fan.
7.1.4 Calculation of
heat exchangers
In contrast to the filter fans, the heat discharge via the switch cabinet sur-
face certainly does need to be taken into account in design of the heat
exchangers. The necessary cooling power QE which a heat exchanger
must deliver is calculated from the difference between the power loss and
the radiated power of the switch cabinet.
QE = QV - QS (3)
Example: A fully exposed sheet-steel switch cabinet is 60 cm wide, 2 m
high and 50 cm deep. The power loss in the cabinet is 900 Watts.
The maximum ambient temperature is +25°C, the temperature in the cab-
inet should not rise above +35°C.
Altitude above sea level [m]
f m³K/Wh)
0 - 100
3.1
100 - 250
3.2
250 - 500
3.3
500 - 750
3.4
750 - 1000
3.5
Tabelle 7.1
Calculation factor “f” for filter fans dependent on altitude above
sea level
V
3 1
,
600
20
--------
m
3
h
-------
⋅
=
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