SIEMENS
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Siemens D 21.4 · 2017
Tools and configuration
Configuration notes
Heat dissipation
13
■
Configuration
(continued)
Power Modules, Motor Modules and Active Line Modules
in frame sizes FX and GX
Active Line Modules in frame sizes HX and JX
Motor Modules in frame sizes HX and JX
Calculation of internal control cabinet temperature
Control cabinet with forced ventilation
In a control cabinet with forced ventilation, the heat loss
P
v
passes to the through-flowing air that then rises in temperature
by
Δ
ϕ
. In the time interval
Δ
t
, the air absorbs the heat
Q
=
c
×
m
×
Δ
ϕ
=
P
v
×
Δ
t
, and at the same time the air volume
V
flows through the control cabinet (
c
is the specific heat capacity
of the air). Mass
m
and volume
V
are linked via density
ρ
.
m
=
ρ
×
V
applies. When inserted in the formula above, the
following equation is obtained:
P
v
=
c
×
ρ
× (
V
/
Δ
t
) ×
Δ
ϕ
The heat loss
P
v
, that can be dissipated by forced ventilation,
is thus proportional to the volume flow
that the fan
delivers through the control cabinet and the permissible degree
of heating
Δ
ϕ
=
T
c
-
T
a
The heat capacity and density of the air depend on the humidity
level and atmospheric pressure. For this reason, the equation is
dependent on other parameters. To estimate the temperature
rise in the control cabinet in a typical industrial environment,
c
= 1 kJ/kg × K and
ρ
= 1.2 kg/m
3
can be assumed. This results
in the following quantity equation:
with
Δ
ϕ
=
T
c
-
T
a
The temperature
T
c
as the ambient temperature of the compo-
nents in the interior of the control cabinet can be estimated with
the formula given and must be checked by means of measure-
ments for each application because local hot spots can form,
e.g. in close proximity to a source of heat or hotspot caused by
unfavorable air circulation.
150
250
Discharged air
Cooling air
G_D211_EN_00026
Cooling air
Discharged air
(5.9 in)
(9.84 in)
150
250
Discharged air
Cooling air
G_D211_EN_00027
Cooling air
(9.84 in)
(5.9 in)
V
V
/∆
t
=
P
[W]
= 1200 ×
V
[m
3
/s]
×
[K]
v
P
v
c
V
T
a
T
G_D211_XX_00228
© Siemens AG 2017