Tech Briefs Magazine - March 2022 - 18

Thermal Management Strategies
Closed-Loop Cooling
COLD
Figure 1: Design engineers must incorporate
thermal management equipment, such as air
conditioners and heaters, into electrical and
electronic enclosures to protect against temperature
and moisture conditions that can lead
to device failures.
HOT
can't be effectively conditioned with
HVAC systems.
Design engineers, therefore, really
need compact, effective, energy-effi cient
thermal management solutions, which
can be installed on a targeted basis as
needed.
Temperature Techniques
Most people are familiar with basic
heaters, air conditioners, and associated
thermostats like those used in cars and
homes. Each of these devices, or industrialized
versions, can be used for conditioning
control panels. But there are
other more specialized devices for the
service (Figure 1).
Here is a rundown of thermal management
devices for enclosure temperature
and moisture control:
* Air conditioner: Air conditioners for
enclosure cooling function are like
consumer versions, but they are packaged
in compact housings rated for
NEMA 12, 4, and/or 4X environments.
They typically use on-board controls
and maintain closed-loop air circulation
within the enclosure, so no extra
moisture or contaminants are introduced
inside (Figure 2). However,
these devices consume signifi cant power,
take up lots of space, and require
periodic service.
* Heater: Heaters for control panel usage
are most often electric-resistance
type and may or may not include controls
on-board. Design engineers need
to ensure these heaters are touch-safe
and mounted in the lower area of the
enclosure.
* Circulating fan: Air conditioners and
some heaters will include a circulating
fan to move air within the enclosure
and promote heat transfer. However,
18
Figure 2: Closed-loop airfl ow, depicted here with an AutomationDirect air conditioner but also possible
with a heat exchanger, ensures that no extra contaminants or moisture is introduced to the
enclosure interior as the temperature is managed.
users can also install separate directional
circulating fans to assist. Another
option, if it is acceptable for outside
air to enter the enclosure, is to install
fi lter fans (or passive louver plates)
that pull cooler outside air into the enclosure
and exhaust hot inside air.
* Thermostat: Some heating and cooling
solutions include on-board digital
or electro-mechanical thermostats for
temperature control, but those that
don't will need a standalone thermostat
wired to perform this function.
Thermostat contacts can also be monitored
by a supervisory control system
for indication and alarming purposes.
* Thermoelectric cooler: Thermoelectric
coolers use the Peltier Effect to
perform cooling, instead of a compressor
like an air conditioner, so they have
fewer moving parts and require virtually
no maintenance.
* Vortex cooler: Vortex coolers use pressurized
air and separate the fl ow into
hot and cold air streams (Figure 3).
The cold stream is applied to the enclosure
interior. Vortex coolers can be
a compact cooling method where larger
devices will not work, and they are
exceptionally reliable and suitable for
operation in harsh environments.
* Heat exchanger: A heat exchanger is
a closed-loop system that simply exchanges
heat inside an enclosure with
a cooler outside environment. Heat exchangers
have a low operating cost and
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are useful when enclosures contain
heat-generating devices, and when the
enclosure is installed in a larger conditioned
space.
* Hygrostat and hygrotherm: Moisture
can build up in any type of enclosure,
even with proper environmental ratings,
because it can be introduced
when the cover is open, or it might intrude
via conduits. Enclosure heaters
can prevent the formation of condensation,
but only if they are controlled
to maintain the relative humidity below
60 percent, which is possible if the
enclosure interior is maintained at a
temperature as little as 9 °F higher
than outside ambient air. A hygrostat
(also known as a humidistat) senses
the relative humidity and can keep
it within prescribed limits. A hygrotherm
performs this task, and it also
performs a dual function by acting as
a thermostat.
Selection and Sizing
Design engineers need to gather information
about the intended installation
to perform the necessary selection
and sizing steps. This requires:
* Evaluating the enclosure contents, how
much heat is internally generated (in
BTU per hour or watts), and at what
temperature ranges those components
are rated to operate.
* Determining the outside ambient temperature
range and if there are addiTech
Briefs, March 2022
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Tech Briefs Magazine - March 2022

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