ECH EVAPORATIVE CONDENSERS
OPERATION
140.910-IOM (DEC 13)
Page 12
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If white deposits form on galvanized steel surfaces after
the pH is returned to normal service levels, it may be
necessary to repeat the passivation process.
NOTICE
Stainless steel cold water basins and basins protected by
the TripleGuard™ Corrosion Protection System or Ther-
mosetting Hybrid Polymer do not require passivation.
However, if the upper structure is galvanized steel, pas-
sivation is required.
BIOLOGICAL CONTROL
•
The warm, oxygen and nutrient rich environment
inside evaporative cooling equipment provides an ideal
environment conducive to 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. To
avoid biological contamination and minimize the risk
of Legionella, initiate the biocide treatment program at
start-up and continue on a regular basis thereafter in
accordance with the treatment supplier’s instructions.
•
Bleed/blowdown or chemical treatment used for corrosion
and scale control alone is not adequate for control of
biological contamination.
•
Introduce solid or granular biocides through a chemical
“pot” feeder installed in parallel with the system circulating
pump. Diluted liquid biocides may be added directly to the
cold water basin.
•
If ozone water treatment is used, at no point should
concentrations exceed 0.5 ppm.
•
Initial Start-up and Start-up Following a Shutdown Period:
1. To minimize the risk of biological contamination
during a shutdown period of three days or more, it
is recommended that the entire system (evaporative
cooling equipment, system piping, heat exchangers,
etc.) be drained.
2. To resume operation of a drained system and at initial
start-up, clean all debris from the cold water basin
and fill the system with fresh water. Then execute
one of the following biocide treatment programs while
operating the circulating pump and prior to operating
the unit fans:
a. Resume treatment with the biocide that was used
prior to shutdown. Then run the pump only while
maintaining the maximum recommended biocide
residual for a sufficient duration (residual and time
will vary with the biocide) as recommended by the
water treatment supplier. Start the fan only after
this treatment period is completed.
b. Check the pH of the circulating water and, if
necessary, adjust it to 7.0 - 7.6 pH. Then, running
the pump only, treat the system with sodium
hypochlorite to maintain a level of 4 to 5 mg/l (ppm)
free chlorine (as Cl2) over a 6 hour period. Test
kits for measuring the free residual of chlorine are
commercially available. Start the fan only after this
treatment period is completed.
c. When it is not practical to drain the system during
shutdown periods, install a bypass line with shutoff
valves to permit the recirculating water to circulate
throughout the system, including the unit basin,
while bypassing the fill section of the evaporative
cooling equipment (fans should remain off).
d. Treat the system as per one of the above-described
methods prior to restarting the unit.
