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•
Corrosion
– Red rust on steel components and white rust on galvanized surfaces may
affect the longevity of system components.
•
Scale Formation
– Scale not only reduces heat transfer and system efficiency, but
also may lead to under deposit corrosion. If scale is not controlled, it may continue
building on critical components such as the fill and severely impact thermal
performance.
•
Biological Fouling
– Slime and algae formations may reduce heat transfer, promote
corrosion, and harbor pathogens such as Legionella.
Corrosion and Scale Control
• To control corrosion and scale, maintain the water chemistry of the recirculating
water within the parameters listed in
Table 5
. The specific measures required vary
from system to system and are dependent on the chemistry of the make-up water, the
metallurgy of the piping and heat transfer devices exposed to the recirculating water,
and the temperatures at which the system will be operating.
• Bleed/blowdown, the continuous flow of a small portion of the recirculating water to
a drain, is used to control the concentration of dissolved solids. On rare occasions,
this may be adequate to control scale and corrosion. More often, chemical scale and
corrosion inhibitors are necessary, which raise the allowable level of dissolved solids
without the risk of scale and corrosion.
• In cases where bleed/blowdown alone is being employed for corrosion and scale
control without chemical treatment your water treatment specialist may recommend
more conservative limits than those shown in
Table 5
.
NOTES:
1.
Galvanized steel units require
passivation in order to prevent
white rust (refer to “Passivation”
on
page 24)
.
2.
Hardness and alkalinity limits
may be exceeded under certain
circumstances. Consult your
water treatment specialist for
recommendations.
3.
The conversion factor used to
determine conductivity is 0.625
(TDS = 0.625 x Conductivity).
Biological Control
• The warm, oxygen and nutrient rich environment inside evaporative cooling equipment
provides an ideal environment for the growth of algae, slime, and other micro-
organisms. Uncontrolled, this can reduce heat transfer, promote corrosion, and
promote the growth of potentially harmful organisms such as Legionella.
Table 5.
Quality Guidelines for Circulating Water
Property of Water
Recommended Level
pH
6.5 to 9.0
[1]
Hardness as CaCO
3
30 to 750 ppm
[2]
Alkalinity as CaCO
3
500 ppm maximum
[2]
Total Dissolved Solids (TDS)
1500 ppm maximum
Conductivity
2400 micromhos
[3]
Chlorides
250 ppm maximum Cl
(410 ppm maximum as NaCl)
Sulfates
250 ppm maximum
Silica
150 ppm maximum
Corrosion Protection
Water Treatment
Corrosion and Scale Control
Biological Control