18
Water Chemistry Parameters
The water treatment program designed for evaporative cooling equipment must be compatible
with the unit’s materials of construction, as well as other equipment and piping used in the
system. Control of corrosion and scale will be very difficult if the recirculating water chemistry is
not consistently maintained within the ranges noted in Table 4. In mixed metallurgy systems, the
water treatment program should be designed to ensure protection of all the components used in
the cooling water loop.
TABLE 4 – Recommended Water Chemistry Guidelines
Property
Z-725
Galvanized Steel
Type 304
Stainless Steel
Type 316
Stainless Steel
pH
7.0 – 8.8
6.0 – 9.5
6.0 – 9.5
pH During Passivation
7.0 – 8.0
N/A
N/A
Total Suspended Solids (ppm)*
<25
<25
<25
Conductivity (Micro-Siemens/cm) **
<2,400
<4,000
<5,000
Alkalinity as CaCO
3
(ppm)
75 - 400
<600
<600
Calcium Hardness CaCO
3
(ppm)
50 - 500
<600
<600
Chlorides as Clˉ (ppm) ***
<300
<500
<2,000
Silica (ppm)
< 150
< 150
< 150
Total Bacteria (cfu/ml)
<10,000
<10,000
<10,000
* Based on standard
EVAPAK
®
fill
** Based on clean metal surfaces. Accumulations of dirt, deposits, or sludge will increase corrosion potential
*** Based on maximum coil fluid temperatures below 49°C
If a chemical water treatment program is used, all chemicals selected must be compatible with the unit’s
materials of construction as well as other equipment and piping used in the system. Chemicals should
be fed through automatic feed equipment to a point which ensures proper control and mixing prior to
reaching the evaporative cooling equipment. Chemicals should never be batch fed directly into the basin
of the evaporative cooling equipment.
Evapco does not recommend the routine use of acid due to the destructive consequences of improper
feeding; however, if acid is used as part of the site specific treatment protocol, it should be pre-diluted
prior to introduction into the cooling water and fed by automated equipment to an area of the system
which ensures adequate mixing. The location of the pH probe and acid feed line should be designed
in conjunction with the automated feedback control to ensure that proper pH levels are consistently
maintained throughout the cooling system. The automated system should be capable of storing and
reporting operational data including pH reading and chemical feed pump activity. Automated pH control
systems require frequent calibration to ensure proper operation and to protect the unit from increased
corrosion potential.
The use of acids for cleaning should also be avoided. If acid cleaning is required, extreme caution must
be exercised and only inhibited acids recommended for use with the unit’s materials of construction
should be used. Any cleaning protocol, which includes the use of an acid, shall include a written
procedure for neutralizing and flushing the evaporative cooling system at the completion of the cleaning.
Control of Biological Contamination
Evaporative cooling equipment should be inspected regularly to ensure good microbiological control.
Inspections should include both monitoring of microbial populations via culturing techniques and visual
inspections for evidence of biofouling.
Poor microbiological control can result in loss of heat transfer efficiency, increase corrosion potential, and
increase the risk of pathogens such as those that cause Legionnaires ’ disease. The site specific water
treatment protocol should include procedures for routine operation, startup after a shut-down period, and
Summary of Contents for AT 110-112
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