Wiegmann ENVIRONMENTAL CONTROLS TECHNICAL DATA
DATA SUBJECT TO CHANGE WITHOUT NOTICE
ENVIRONMENTAL CONTROL
TECHNICAL DATA
L14
Ever since components have been made to control electrotechnical tasks, heat loss has been a subject to take into
consideration. Sometimes more—sometimes less.
Major problems with heat caused excessive dust accumulation in switchgear equipment because the doors were left
open during the summer to allow the equipment to cool
down. This can result in fluctuations in temperature. These
lead to stress situations that can considerably reduce the
service life of electronic components (see chart).
THREE BASIC COOLING METHODS
When selecting a cooling method there are three types
to consider:
1. Natural Convection — If there is only a minimal heat
gain in your circumstance, use of louvers or grilles with
filters can be effective. This method, however, usually
provides less cooling effect than is necessary with
today’s components (Fig. 1, pg. L15).
2. Forced Convection Air Cooling — If the installation
will be in a clean, non-hazardous environment with an
acceptable ambient (outside the enclosure) temperature
range, a simple forced-air cooling system utilizing outside
air is usually adequate. Combined with an air filter, such
devices generally meet the heat removal needs of typical
electronic equipment and many electrical applications
(Fig. 2a & 2b, pg. L16). Examples of forced convection
air cooling are Filterfans™ and Box Fans.
3. Closed-Loop Cooling — In harsh environments
involving high temperatures, wash-down requirements,
heavy particulate matter or the presence of chemicals
capable of damaging components (NEMA 4 or 12
environments), ambient air must be kept out of the
enclosure. Closed-loop cooling consists of two separate
This chart demonstrates the relationship between temperature and service life.
circulation systems. One system seals out the ambient
air, cooling and recirculating clean, cool air throughout
the enclosure. The second system uses ambient air or
water to remove and discharge the heat (Fig. 3, pg. L18).
Examples of closed-loop cooling equipment employed
with electronics and process controls are air conditioners
and heat exchangers.
Heat Abduction by Natural Convection
If the ambient temperature is lower than the temperature
inside the switch cabinet, the dissipated heat escapes into
the atmosphere through the surface of the switch cabinet.
The following simple equation is used to calculate the level
of heat radiated from a switch cabinet:
PR[W} = c x A x DT
P
R
[Watt]: Radiation Power
Thermal power radiated from the surface area
of the switch cabinet into the ambience or radiated from the ambience into the switch cabinet.
C[W/m
2
K]: Coefficient of heat transmission
Radiation power per 1m2 surface area and 1K
difference in temperature. This constant is
determined by the material:
Sheet steel -5.5 W/m2K
Stainless steel -3.7 W/m2K
Aluminum -12.0 W/m2K
Plastic -0.2 W/m2K
A[m
2
]: Surface area of switch cabinet
Effective surface area of a switch cabinet
measured according to the specifications of
VDE0660, Part 506.
∆T[K]: Difference in temperature between the
ambience and inside the switch cabinet
Surface area of switch cabinet A[m2]
Heat radiation P[W]
DATA SUBJECT TO CHANGE WITHOUT NOTICE
ENVIRONMENTAL CONTROL
TECHNICAL DATA
L15
Heat Abduction with Filterfans
™
Follow the simple equation for calculating the required
air flow volume:
V[m3/h]: Flow volume for a filter fan
Pd[Watt]: Dissipation loss
Thermal power generated inside a switch
cabinet by dissipation loss from components.
A[m2]: Difference in temperature between the
ambience and inside the switch cabinet
In the course of development, absolute priority was given
to the use of high-quality components (plastic material, fan,
filter mat) and comprehensive transparent technical data.
For this purpose we measured every Filterfan
™
and exhaust
filter in a test laboratory.
When considering the use of Filterfans™:
• Always use the Filterfan
™
to propel the cool ambient air
into the switch cabinet. This ensures that slight positive
pressure builds up inside the switch cabinet in comparison
to the ambience and that only air filtered by the Filterfan
™
flows into the switch cabinet. The air propelled into the
cabinet displaces the warm air which exits through the
exhaust filter. If, however, the air is drawn out of the switch
cabinet by suction power, unfiltered air can also enter
through gaps and components
• If you install a combination of Filterfan
™
/exhaust filter, fit
the Filterfan
™
in the lower third of the switch cabinet if
possible. The exhaust filter must be installed as near to
the top as possible to prevent heat pockets in the upper
part of the cabinet
• In switch cabinets consisting of several compartments,
the cool air capacity required should be divided among
two or more Filterfans
™
/exhaust fans. This measure helps
to ensure a more acceptable distribution of temperature
throughout the cabinet
• If you combine a Filterfan
™
with two exhaust filters, the
cool air divides into “Y” shape. In this way, with just one
additional exhaust filter you can considerably improve
the circulation inside the switch cabinet
• Install a thermostat that only trips the Filterfan
™
when
the temperature is too high. This can quite substantially
increase the service life of your filter mat
Natural Convection
Figure 1
(European Patent No. 0439667)
The Filterfan/exhaust filter is centered in the cutout
and held in place across the 4 corners. Installation
time is thus reduced from 12 minutes to virtually
ZERO.
V=
3.1(Pd)
[m3/h]
∆T
Loading...