Feature
low total bacteria counts are a sign of a biologically inactive
system regardless of the presence or absence of algae.
Algae growth may be particularly noticeable during the
spring and summer. As previously noted, algae requires
sunlight to grow; therefore, open cooling systems and
systems that receive direct sunlight are more prone to algae
growth. Blown-in dirt and nutrients also promote algae
growth.
The use of filtration systems to relieve the system of
blown-in and precipitated solids can reduce the area for algae
to thrive. Effective filtration will not remove existing algae but
should prevent future blooms.
LOCATION
Each cooling tower, evaporative cooler or condenser should
be located and positioned to prevent introduction of the
discharge air and the associated drift which may contain
contaminants, such as legionella.
Piping should be sized and installed in accordance with rules
of good practice. Dead legs and stagnant water conditions
in the piping should be avoided. If more than one inlet
connection is required, balancing valves should be installed
to properly balance the flow to each inlet. Depending on
the design of the hydraulic circuit, it may also be necessary
to install balancing valves at the suction connections of the
towers. The use of shut-off valves is dictated by the necessity
to (automatically or manually) isolate cells or towers for
capacity control or servicing. If the equipment is installed
on vibration rails, compensators must be installed in the
connecting piping.
WINTER SAFETY
When a unit is shut down in freezing weather, the basin water
must be protected by draining to an indoor auxiliary remote
sump tank or by providing supplementary heat to the cold-
water basin. Supplementary heat can be provided by electric
immersion heaters or in some cases, hot water, steam coils, or
steam injectors.
All exposed water piping, make-up lines, and spray pumps
(if applicable) that do not drain at shutdown should be
strapped with electric heater tape and insulated. When dry
operation is planned for low ambient conditions, centrifugal
fan units should be supplied with oversized fan motors
to prevent motor overload when the spray water is not
operating. For remote sump applications, the spray water
pump must be selected for the required flow at a total head
which includes the vertical lift, pipe friction (in supply and
suction lines) plus the required pressure at the inlet header of
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PIPING
the water distribution system (14 kPa). A valve should always
be installed in the discharge line from the pump to permit
adjusting flow to the unit requirement. Inlet water pressure
should be measured by a pressure gauge installed in the
water supply riser at the spray water inlet and adjusted to the
specified inlet pressure.
Unless the system is shut down and drained during
winter, measures must be taken to protect the system from
freezing during the winter, during operation and standstill.
Freeze protection during operation is achieved by selecting
an adequate method of capacity control. For reasonably
constant loads and cooling water or condensing temperatures
above 15°C step control is usually adequate. For variable
loads, in particular when combined with free cooling,
modulating controls are recommended.
When the equipment is shut down in freezing weather the
sump water must be protected. This can be accomplished
by the installation of electrical sump heaters. The standard
electric heaters are sized to maintain +4°C sump water when
the ambient temperature drops to - 8°C. RACA
RACA Journal I January 2020
Proper mining
ventilation is
crucial for the
wellbeing of
miners and the
operation.
47