Part 4 Bleed Rate - BAC HXV Operation & Maintenance Manual

HXV HYBRID COOLER
Bleed Rate
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 3, on page 23.
• Replenish the "bleed" water with fresh make-up water, thereby limiting the build-up
of impurities.
• Bleed/blowdown:
– Accomplish the bleed automatically through a solenoid valve controlled by a
conductivity meter. The set point is the water conductivity at the desired cycles of
concentration and should be determined by a competent water treatment expert.
4
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.
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.
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