MIL-HDBK-1165
c) Install a timer to shut off the cooling tower when
cooling is not needed, such as at night when the facility is
unoccupied.
d) Sidestream filtration - water is temporarily routed
away from the cooling tower through special filters that filter
out particles and suspended solids. The cleansed water is then
returned to the cooling tower for use, thus reducing bleed-off.
The cost of implementing a sidestream filtration system is
moderate and requires the addition of energy to run the water
pumps. Also, some solids are not as effectively removed as
others.
5.4.1.4
Replacements. Replacing a cooling tower system is a
large financial investment and is generally not cost-effective
unless the existing cooling tower is extremely old, corroded, or
malfunctioning and un-repairable. It is the incorporation of the
above suggested procedures and retrofits which make the real
difference in water use. Once-through cooling systems, on the
other hand, should be eliminated when possible, since they waste
significant amounts of water by not recirculating it. They can
be replaced by air-cooled models.
5.4.1.5
Chemical Additives. The quality of the air stream
through the cooling tower and the quality of the make-up water
are the major contributors to the quality of the circulating
water. Accumulation of contaminants from these sources in the
circulating water can lead to scale, corrosion, and biofouling of
the cooling tower. Scale is a film of mineral deposits which
forms on the surfaces of the circulating plumbing, causing a
reduction in water flow and thermal efficiency. Corrosion in the
cooling water system results from the water being too acidic,
containing a large concentration of metals (causing galvanic
corrosion), or being too high in oxygen content. Biofouling is
caused by the growth of algae or bacteria in the water to the
point that it impedes proper water flow.
a) Chemicals. Chemicals are generally needed in
cooling towers to control these contaminants that necessitate
bleed-off. By controlling scale, corrosion, biofouling, and
other foreign matter; chemicals reduce the amount of bleed-off
required and thus conserve water. Organophosphates are typically
used as scale and corrosion inhibitors, while a number of
biocides, such as chlorine, inhibit fouling. These chemicals are
best introduced into the cooling tower system by automatic
feeders that respond to the conductivity of the circulating
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