Water Chemistry Parameters; Control Of Biological Contamination - EVAPCO ATC-E Operation And Maintenance Instruction Manual

Operation and Maintenance Instructions
• Operating galvanized evaporative cooling equipment with a water pH below 6 .0 for any period may cause removal of the
protective zinc coating .
• Operating galvanized evaporative cooling equipment with a water pH above 9 .0 for any period may destabilize the
passivated surface and create white rust .
• Re-passivation may be required at any time in the service life of the equipment if an upset condition occurs which
destabilizes the passivated zinc surface .
For more information on passivation and white rust, please request a copy of EVAPCO's Engineering Bulletin 36 .

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 .
Property
pH
pH During Passivation
Total Suspended Solids (ppm)
Conductivity (Micro-Siemens/cm) *
Alkalinity as CaCO
Calcium Hardness CaCO
Chlorides as Cl - (ppm) **
Silica (ppm)
Total Bacteria (cfu/ml)
* 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 system lay-up, if applicable . If excessive microbiological
contamination is detected, a more aggressive mechanical cleaning and/or water treatment program should be undertaken .
It is important that all internal surfaces, particularly the basin, be kept clean of accumulated dirt and sludge . Additionally, drift
eliminators should be inspected and maintained in good operating condition .
Z-725
Galvanized Steel
7 .0 – 8 .8
7 .0 – 8 .0
<25
<2,400
(ppm) 75 - 400
3
(ppm) 50 - 500
3
<300
<150
<10,000
TABLE 4 – Recommended Water Chemistry Guidelines
Type 304
Stainless Steel
6 .0 – 9 .5
N/A
<25
<4,000
<600
<600
<500
<150
<10,000
21
Type 316
Stainless Steel
6 .0 – 9 .5
N/A
<25
<5,000
<600
<600
<2,000
<150
<10,000