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MCW Cooling Tower
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Engineering Data: Water Quality
21
The MCW cooling tower can be a very effective
air washer. Atmospheric dust able to pass through
the relatively small louver openings will enter the
recirculating water system. Increased concentrations
can intensify systems maintenance by clogging screens
and strainers—and smaller particulates can coat system
heat transfer surfaces. In areas of low flow velocity—
such as the collection basin—sedimentary deposits can
provide a breeding ground for bacteria.
In areas prone to dust and sedimentation, you
should consider installing some means for keeping
the collection basin clean. Typical devices include side
stream filters and a variety of filtration media.
Blowdown
Blowdown or Bleedoff is the continuous removal of
a small portion of the water from the open recirculating
system. Blowdown is used to prevent the dissolved
solids from concentrating to the point where they will
form scale. The amount of blowdown required depends
on the cooling range—the difference between the hot
and cold water temperatures of the closed circuit— and
the composition of the makeup water.
Water Treatment
To control the buildup of dissolved solids resulting
from water evaporation, as well as airborne impurities
and biological contaminants including Legionella,
an effective consistent water treatment program is
required. Simple blowdown may be adequate to control
corrosion and scale, but biological contamination can
only be controlled with biocides.
An acceptable water treatment program must be
compatible with the variety of materials incorporated
in a cooling tower—ideally the pH of the recirculating
water should fall between 6.5 and 9.0. Batch feeding
of the chemicals directly into the cooling tower is not
a good practice since localized damage to the cooling
tower is possible. Specific startup instructions and
additional water quality recommendations can be found
in the MCW Cooling Tower User Manual which
accompanies the cooling tower and also is available
from your local Marley sales representative.
CAUTION
The MCW cooling tower must be located at such
distance and direction to avoid the possibility
of contaminated discharge air being drawn into
building fresh air intake ducts. The purchaser should
obtain the services of a Licensed professional
Engineer or Registered Architect to certify that the
location of the cooling tower is in compliance with
applicable air pollution, fire and clean air codes.