ASHRAE Journal Supplement - AMCA InMotion - November 2023 - 29

PHOTO C. Air-cooled-chiller sound wall skirted
with acoustic louvers. Photo courtesy of Kinetics Noise
Control Inc.
PHOTO D. Induced-draft cooling towers with
rectangular intake and discharge silencers.
Photo courtesy of Kinetics Noise Control Inc.
less than recommended by the chiller manufacturer
but within the limits of the local electrical code, a
double-walled barrier with a skirt of fi xed-blade acoustic
louvers along the bottom of each wall parallel to the
long dimension of the chiller (Photo C) will work. This
design provides a supply of fresh ambient air along the
bottom of the barrier-wall system, avoids any recirculation
of heated air, and is focused on low pressure loss
and required attenuation.
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If the distance between a barrier wall and a chiller is
less than recommended by the chiller manufacturer but
within the limits of the local electrical code and there
is a need to control the noise propagating from the top
of the barrier-wall system, an enclosure with acoustical
louvers and roof baffl es can be used to achieve a noise
reduction of up to 10 dBA above the chiller.
Regardless of the combination used, it is important
to achieve maximum noise control with minimal pressure
loss.
Induced-draft cooling towers. The most
common type of cooling tower consists of a large propeller
fan discharging air upward, with air drawn into intakes
on the sides and passed through a stream of water, some
of which evaporates into the air stream, causing cooling.
Induced-draft-cooling-tower noise is a combination of
low-frequency fan noise; blade-passage tone (below 63
Hz); noise from the spraying and splashing of water; noise
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from the motor, belt, or gearbox; noise associated with
fan speed (noise increases with fan speed); and discharge
noise (typically 5 dB greater than intake noise).
Noise-control options consist of change of location
and orientation, cooling-tower oversizing (expensive),
low-noise fans, motor control (day-night operation,
etc.), double-walled barriers, and intake and discharge
silencers (Photo D).
Where cooling-tower noise control is concerned,
materials of construction are important; budget, operating
environment, and product lifespan all should be
considered. The discharge air is 100-percent saturated
with water vapor. Although stainless-steel discharge
silencers work best, an owner looking to save costs
may elect to go with G90 galvanized steel for an entire
project, with the structural-steel support frame being
factory-hot-dip-galvanized. In such cases, the owner
will need to implement a strict maintenance program
to prevent corrosion.
Noise-Control Products
Ventilation silencers, fi xed-blade acoustic louvers, doublewalled
barriers and enclosure panels, noise-control
pergolas/stacks, and sound absorbers are all viable means
of solving environmental-noise issues.
Ventilation silencers. Ventilation silencers
are used to attenuate fan and cooling equipment and
2023 AMCA inmot ion 29
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ASHRAE Journal Supplement - AMCA InMotion - November 2023

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