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6. Bleed Rate
NOTE: A proper water treatment program, administered under the supervision of a competent
water treatment specialist, is an essential part of routine maintenance to ensure the safe
operation and longevity of evaporative cooling equipment, as well as other system components.
In evaporative cooling, evaporation of a small portion of the recirculating spray water as it flows through the equipment causes
the cooling effect. As this water evaporates, the impurities originally present remain in the recirculating water. The
concentration of the dissolved solids increases over time and can reach unacceptable levels. In addition, airborne impurities
are often introduced into the recirculating water. If these impurities and contaminants are not effectively controlled, they can
cause scaling, corrosion, and sludge accumulations that reduce heat transfer efficiency and increase system operating costs,
potentially shortening the useful life of the equipment. The degree to which dissolved solids and other impurities build up in the
recirculating water may be defined as the cycles of concentration. Specifically, cycles of concentration equal the ratio of the
concentration of dissolved solids (for example - chlorides, sulfates, etc.) in the recirculating water to the concentration of the
same material in the make-up water.
•
In order to optimize heat transfer efficiency and maximize equipment life, bleed or blowdown a small amount of
recirculating water from the system. This controls the cycles of concentration to maintain the quality of the recirculating
water within the guidelines given in Table 5.
•
Replenish the "bleed" water with fresh make-up water, thereby limiting the build-up of impurities.
•
Bleed/blowdown:
To minimize water usage, accomplish the bleed automatically through a solenoid valve controlled by a
o
conductivity meter. The set point is the water conductivity at the desired cycles of concentration and should be
determined by a water treatment expert.
Bleed Line Calculations: The approximate design evaporation rate (E) can be determined by any one of the following
methods:
•
The evaporation rate is approximately 2 USGPM per 1 million BTUH of heat rejection.
•
The evaporation rate is approximately 3 USGPM per 100 tons of refrigeration.
•
Evaporation Rate = Q (USGPM) * R * 0.001.
NOTE: The solenoid valve and conductivity meter must be supplied by others. Evaporation is
proportional to the load and will vary seasonally. BAC recommends the use of a conductivity
meter to maximize water conservation.
Vertex™ Evaporative Condenser Operation & Maintenance Manual – Bleed Rate
Page | 35
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