Prevention Of Condensation In Equipment Cooled By Air Conditioners And Climate Control Systems - Siemens SINAMICS G130 Engineering Manual

General Engineering Information for SINAMICS
Engineering Information
3.6.6 Prevention of condensation in equipment cooled by air conditioners and climate control
systems
Use of air conditioners to cool cabinets
When air conditioners are used to cool the air inside SINAMICS cabinet units, it must be noted that the relative
humidity of the air expelled by the air conditioner increases as a result of the conditioner's cooling effect and that it
might then drop below the dew point. The dew point is the temperature at which water vapor contained in the air
condenses into water. Condensation water can cause corrosion and electrical damage such as, for example,
flashovers in the power units installed inside the cabinet and, in the worst-case scenario, can result in irreparable
equipment damage. It is therefore absolutely essential to prevent condensation inside the units.
The table below specifies the dew point as a function of ambient temperature T and relative air humidity Φ for an
atmospheric pressure of 100 kPa (1 bar), corresponding to an installation altitude of 0 to approximately 500 m above
sea level. Since the dew point drops as the air pressure decreases, the dew point values at higher installation
altitudes are lower than the specified table values. It is therefore the safest approach to engineer the coolant
temperature according to the table values for an installation altitude of zero.
Ambient
temperature
10 ℃
T
20 %
20 ℃ < 0 °C < 0 ℃
25 ℃ 0.6 ℃
30 ℃ 4.7 ℃
35 ℃ 8.7 ℃
40 ℃
45 ℃
12.8℃
50 ℃
16.8℃
20.8℃
Dew point as a function of ambient temperature T and relative air humidity Φ for installation altitude zero
The table indicates that with high relative air humidity even slight cooling of the air by an air conditioner can lead to
condensation. When air conditioners are used, there-
fore, air baffles must be fitted or a minimum
clearance of about 200 mm provided between the air
outlet of the air conditioner and the installed drive
equipment so as to ensure that the cold, moist air
expelled by the air conditioner can mix with the warm,
dry air inside the cabinet before it comes into the
drive equipment installed in the cabinet. By ensuring
that the expelled cold air can mix as required with the
warm, dry cabinet air, it is possible to reduce the
relative air humidity to non-critical values.
Condensate drainage
Condensate starts to form when the cabinet doors
are closed and the air conditioner starts up. The
formation of condensate increases if there are leaks
in the cabinet or if the cabinet doors are open. This
condensate must be drained from the cabinet without
compromising the degree of protection according to
IEC 60529.
It is recommended that the cooling units should be
switched off by door contact switches when doors are
open.
When the cooling unit is mounted on the roof of the
cabinet, it is particularly important to ensure that
condensate cannot drip into the drive equipment
installed inside the cabinet.
Condensate must be either trapped or evaporated.
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< 0 ℃ < 0 ℃ 0.2 ℃
30 % 40 % 50 %
2.0 ℃ 6.0 ℃ 9.3 ℃
6.3 ℃
10.5℃ 13.8℃
10.5°C
14.9℃ 18.4℃
14.8℃ 19.3℃ 22.9℃
19.1℃ 23.7℃ 27.5℃
23.3℃ 28.2℃ 32.0℃
27.5°C
32.6℃ 36.6℃
Relative air humidity Φ
2.7 ℃ 4.8 ℃ 6.7 ℃
60 % 70 % 80 %
12.0℃ 14.3℃ 16.4℃
16.7℃ 19.1℃ 21.2℃
21.3℃ 23.8℃ 26.1℃
26.0℃ 28.6℃ 30.9℃
30.6℃ 33.4℃ 35.8℃
35.3℃ 38.1℃ 40.6℃
40.0℃ 42.9℃ 45.5℃
Correct air guidance prevents condensation inside
the drive equipment
7.6 ℃ 8.4 ℃ 9.2 ℃
85 % 90 % 95 %
17.4℃ 18.3℃ 19.1℃
22.2℃ 23.2℃ 24.1℃
27.1℃ 28.1℃ 29.0℃
32.0℃ 33.0℃ 34.0℃
36.9℃ 37.9℃ 38.9℃
41.8℃ 42.9℃ 43.9℃
46.6℃ 47.8℃ 48.9℃
100 %
10.0℃
20.0℃
24.9℃
29.9℃
34.9℃
39.9℃
44.9℃
49.9℃