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1. Ensure all controls for capacity and freeze protection
are set properly and functioning normally.
2. Prevent excessively high water levels and possible
overflow of the cold water basin due to over pumping,
clogged strainers, or make-up valve malfunction.
Water Treatment
Corrosion and Scale Control
In cooling towers, cooling is accomplished by the evapor-
ation of a portion of the process water as it flows through
the tower. As this water evaporates, the impurities originally
present remain in the re-circulating water. The concen-
tration of the dissolved solids increases rapidly and can
reach unacceptable levels. In addition, airborne impurities
are often introduced into the re-circulating water, intensi-
fying the problem. If these impurities and contaminants
are not effectively controlled, they can cause scaling,
corrosion, and sludge accumulations which reduce heat
transfer efficiency and increase system operating costs.
The degree to which dissolved solids and other impurities
build up in the re-circulating water may be defined as the
cycles of concentration. Specifically, cycles of concentra-
tion is the ratio of dissolved solids (for example – Totally
Dissolved Solids (TDS), chlorides, and sulfates) in the re-
circulating water to dissolved solids in the make-up water.
For optimal heat transfer efficiency and maximum
equipment life, the cycles of concentration should be
controlled such that the re-circulating water is main-
tained within the guideline list below.
Stainless Steel or
Baltibond
Corrosion
Protection System
pH
6.5 to 9.0
Hardness as
30 to 500 ppm
CaCO
3
Alkalinity as
500 ppm max.
CaCO
3
Total
Dissolved
1200 ppm max.
Solids
Chlorides
250 ppm max.
Sulfates
250 ppm max.
10
®
G235
Galvanized
Steel
1
2
7.30 to 9.0
30 to 500 ppm
500 ppm max.
1000 ppm max.
125 ppm max.
125 ppm max.
3. Discover any icing conditions that may develop before
they reach the point where the tower or supports are
damaged or system performance is impaired.
For more detailed information on winter operation and for
recommended operating procedures on specific installa-
tion, contact your local B.A.C. Representative.
Re-circulated Water Quality Guideline,
1
Units manufactured in Canada will be constructed of the
metric equivalent Z700 galvanized steel.
2
Units having galvanized steel construction and a
circulating water pH of 8.3 or higher will require periodic
passivazation of the galvanized steel to prevent 'white
rust', the accumulation of white, waxy, non-protective zinc
corrosion products on galvanized steel surfaces.
In order to control the cycles of concentration such that
the above guidelines are maintained, it will be necessary
to "bleed" or "blowdown" a small amount of re-circulating
water from the system. This "bleed" water is replenished
with fresh make-up water, thereby limiting the build-up of
impurities.
Typically the bleed is accomplished automatically through
a solenoid valve controlled by a conductivity meter. The
conductivity meter set point is the water conductivity at
the desired cycles of concentration and should be deter-
mined by a competent water treatment expert. (Note: The
solenoid valve and conductivity meter must be supplied
by other vendors) Alternatively, a bleed line with a valve
can be used to continuously bleed from the system.
(Note: The bleed line and valve must be supplied by
other vendors) In this arrangement, the rate of bleed can
be adjusted using the valve in the bleed line and mea-
sured by filling a container of known volume while noting
the time period. The bleed rate and water quality
should be periodically checked to ensure that ade-
quate control of the water quality is being maintained.
The required continuous bleed rate may be calculated by
the formula:
Bleed Rate = Evaporation Rate/Number of Cycles of
Concentration –1
The evaporation rate can be determined by one of the
following:
The evaporation rate is approximately 2 GPM per 1
million BTU/HR of heat rejection.
The evaporation rate is approximately 3 GPM per 100
tons of refrigeration.
Evaporation Rate = Water Flow Rate x Range x .001
Example: At a flow rate of 900 GPM and a cooling
range of 10˚F, the evaporation rate is 9 GPM
(900 GPM x 10˚F x .001 = 9 GPM).
If the site conditions are such that constant bleed-off will
not control scale or corrosion and maintain the water
quality within the guidelines, chemical treatment may be
necessary. If a chemical treatment program is used, it
must meet the following requirements:
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