10
System Off / No Load
The system pumps and fans are off. If the basin is full of water a minimum basin water temperature of 40ºF must be maintained to prevent
freezing. This can be accomplished with the use of optional basin heaters. See the “Cold Weather Operation” section of this bulletin for
more details on cold weather operation and maintenance.
System/Condensing Temperature Rises
The recirculation pump turns on. The unit will provide approximately 10% cooling capacity with only the pump running. If the unit has
positive closure dampers they should be fully opened before the pumps turn on.
If the system temperature continues to rise, the unit fan is cycled on. For a variable speed controller, the fans are turned on to minimum
speed. See the “Fan System – Capacity Control” section of this bulletin for more details on fan speed control options. If the system
temperature continues to rise, then the fan speed is increased as required, up to full speed.
Note: During sub-freezing weather the minimum recommended speed for variable speed controllers is 50%. ALL FANS IN OPERATING
CELLS OF MULTIPLE CELL UNITS MUST BE CONTROLLED TOGETHER TO PREVENT ICING ON THE FANS.
System/Condensing Temperature Stabilizes
Control the leaving fluid temperature (closed circuit coolers) or condensing temperature (evaporative condensers) by modulating the fan
speeds with variable speed drives or by cycling fans on and off with single or two-speed drives.
System/Condensing Temperature Drops
Decrease the fan speed, as required.
System Off / No Load
The system pump turns off. The starter interlock will energize any optional basin heaters in cold weather.
The recirculation pump should not be used as a means of capacity control, and should not be cycled frequently. Excessive cycling can
lead to scale build-up, and reduce wet and dry performance.
Dry Operation
During colder winter months it is possible to turn off the spray pump, drain the cold water basin, and just cycle the fans. Be sure to leave
the basin drain open during this time to prevent collection of rain water, snow, etc. If the unit has positive closure dampers they should be
fully opened before the fans turn on. If dry operation will be used on a centrifugal fan, forced dra unit, be sure to verify that the motor
and drives have been properly sized to handle the reduction in static pressure experienced when the spray water is turned off.
NOTE: Minimum control point for process fluid should never be lower than 42º F.
NOTE: When a unit is provided with a discharge damper assembly, the control sequence should cycle the dampers open
and closed once a day regardless of capacity requirments to prevent the assembly from seizing. The fan motor should be
shut off whenever the dampers are closed.
NOTE: ESW4/A or PHC product lines should not operate dry.
NOTE: The eco-ATW/eco-ATWE sequence of operation is unique and is explained in detail in the Sage
2
, Sage
3
Panel
Control Manual.
Basic Closed Circuit Cooler/Condenser Sequence of Operation
for Wet or Evaporative Mode
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