CE Pro January 2023 - 58

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Addressing 3 Myths About AV Rack Cooling
Doesn't modern gear generate less heat? Aren't preinstalled fans good enough? Think again before finishing up your next rack.
YOU'VE DESIGNED and
spec'd a killer AV system
and it's time to prep that
stack of equipment into
its proper rack placement.
You've outfitted equipment
racks full of gear countless
times, so no problem, right?
Every AV system installation
has the potential
for problems, so let's try
to prevent any that may
arise due to overheating
rack systems. Here are
three myths about AV rack
cooling to consider on your
next job.
Myth 1: You don't need
cooling; today's digital
gear generates much less
heat than analog gear did.
Is that really the case?
Digital amplifiers may be
more efficient than traditional
class AB amplifiers
(we won't talk about Class
A or tube-type systems)
at full power output, but
unless your clients are listening
to sine waves at full
power, digital/switch-mode
amps still consume more
power at low to moderate
listening levels than is delivered
to the speakers.
That difference shows
58 | CE Pro January 2023
up as heat.
It's true that if you only
consider the output stages,
switch-mode amps are
efficient at lower power
levels, but when the
power required for circuitry
" overhead " - i.e., low-level
stages, analog-to-digital
conversion, power supply
regulators, etc. - are included,
efficiency drops.
Also, while some gear
is no longer widely used
(remember DVD players?),
home networking equipment
is being added as AV
systems start looking more
like IT installations.
Myth 2: Just use racks
that come with fans installed
- problem solved!
Not quite. Almost all
preinstalled rack fans
lack automatic thermal
controls to turn them on
only when needed and are
rarely quiet; most are AC
powered. AC fans move a
lot of air but generate high
levels of motor noise and
air " whoosh " sounds.
These fans are always
installed in the top cover of
the rack; top-mounted fans
tend to draw most fresh
air in near the top of the
rack, even when side and
back panels are installed;
there's little air flow near
the bottom.
If most heat is generated
near the bottom of the
rack (where large amplifiers
might be located for seismic
considerations), they
typically get little cooling
from top-mounted fans.
So, we have loud fans
that must be turned on and
off manually... not a happy
or efficient situation.
The better approach is
to put cooling systems into
the rack where needed
- just above a major
heat-generator with a vent
panel below, perhaps? That
can be an effective solution
unless there's a closed door
in front of the rack.
If there is, rear-mounted
fans can be used, but only
if there's no rear door on
the equipment rack to
block airflow. If there are
front and rear doors, heat
generators may have to
be relocated to the top of
the rack and top-mounted
fans installed.
Myth 3: We've cooled
the rack - we're done.
Again, not so fast. If
the rack is free-standing,
you may be finished, but
in many installations it's
tucked into a cabinet or
closet. It's not enough to
move the heat out of the
rack and into the cabinet;
you also have to move
it out of the cabinet or
the same hot air will just
circulate while increasing in
temperature.
There are cooling systems
available to mount in
cabinet sides or closet walls
to exhaust heated air into
an adjacent hallway or utility
room, and fresh air can
be brought in (passively)
through a 3/8- to ½-inch gap
under the door or a grille
set into the door.
Also, if the rack has
several open positions
allowing air to circulate
through it, a properly
sized closet/cabinet cooling
system can make it
unnecessary to install fans
in the rack itself.
Author FRANK FEDERMAN
is CEO of Active Thermal
Management.
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CE Pro January 2023

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