Biological Control; Chemical Treatment; Passivation - Baltimore Aircoil Company VFL Series Operating And Maintenance Instructions Manual

Biological control

The growth of algae, slimes and other micro-organisms, if uncontrolled, will reduce system efficiency and may
contribute to the growth of potentially harmful micro-organisms, such as Legionella, in the recirculating water
system.
Accordingly a treatment programme specifically designed to address biological control should be initiated when the
system is first filled with water and administered on a regular base thereafter in accordance with any regulations
(national, regional) that may exist or in accordance with accepted codes of good practice, such as EUROVENT
9-5/6, VDMA Detailsheet 24649 etc.
Also during shutdown periods it is recommended to continue the water treatment programme. Alternatively, the
basin and pump should be drained.
It is strongly recommended to monitor the bacteriological contamination of the recirculating water on a regular base
(for example, TAB test with dip slides on a weekly base) and record all results.
Certain products used for water treatment, particular some dispersant and bio-dispersant additives, might change
the properties of the water (such as the surface tension), which can cause excessive drift loss (water passing
through the eliminators). In such case we recommend to review the water treatment (product type, dosage) with
your water treatment expert.
In case of doubt, a short test can be performed, after cleaning & disinfection, using fresh water without addition of
the concerned chemical (within the limits of the local legislation).

Chemical treatment

1. Water treatment chemicals or non-chemical systems need to be compatible with the materials of construction
used in the cooling system including the evaporative cooling equipment itself.
2. In case of chemical water treatment, chemicals should be added to the recirculating water by an automatic
feed system. This will prevent localised high concentrations of chemicals, which may cause corrosion.
Preferably the water treatment chemicals should be fed into the cooling system at the discharge of the
recirculation pump. The chemicals should not be fed in concentrated form, nor batch fed directly into the cold
water sump of the evaporative cooling equipment.
3. BAC specifically discourages acid dosing as mean of scale control (unless under certain strict circumstances
for open circuit cooling towers with very large system volume and remote sump, or constructed from stainless
steel).
4. A competent water treatment company should be consulted for the specific water treatment programme to be
applied. Next to the supply of dosing and control equipment and chemicals, the programme should include
regular monthly monitoring of the circulating and make up water quality.
5. If it is proposed to operate a treatment programme outside the BAC Water Quality Control Guidelines, the BAC
factory warranty may be invalidated if the water quality is persistently outside the Control Guidelines, unless
specific prior written BAC approval. (Some parameters may be exceeded under certain strict circumstances.)
It is strongly recommended to check the key parameters of the circulating water quality on a monthly base. See
table: "Circulated water quality guidelines". All test results need to be recorded.

Passivation

When new systems are first commissioned, special measures should be taken to ensure that galvanized steel
surfaces are properly passivated to provide maximum protection from corrosion. Passivation is the formation of a
protective, passive, oxide layer on galvanized steel surfaces.
To ensure that galvanized steel surfaces are passivated, the pH of circulating water should be kept between 7.0
and 8.2 and calcium hardness between 100 and 300 ppm (as CaCO
new zinc surfaces turn dull grey in colour. 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.
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) for four to eight weeks after start-up, or until
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