Marley
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MD Cooling Tower
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Engineering Data: Water Quality
27
The MD 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.
CAUTION
The MD 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.
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 MD
Cooling Tower User Manual which accompanies the
cooling tower and also is available at spxcooling.com.
