9
to obtain the desired pressure and maintain proper water distribution. An SPX Cooling
Technologies engineer can advise minimum and maximum flow rates for even distribution.
COLD WATER COLLECTION BASIN
–A suitable depth must be maintained to keep
the pumps from pulling air into the line. The amount of “make-up” water required to keep
the water in the collection basin at the required depth depends upon the “evaporation
loss” and “blowdown” .
FAN DRIVE
–When using two-speed motors, allow a time delay of 20 seconds minimum
after de-energizing the high-speed winding and before energizing the low-speed winding.
Tremendous stresses are placed on driven machinery and motors unless the motors are
allowed to slow to low-speed RPM or less before the low-speed winding is energized.
FREEZING WEATHER OPERATION
–During periods of cold temperature operation,
35°F to 40°F or below, ice will form on the relatively dry parts of the cooling tower that
are in contact with the incoming air. Primarily, this includes the air inlet and adjacent
structural framing. Your understanding of cold weather operation will be enhanced if
you read
“Cooling Towers and Freezing Weather”
Marley Technical Report H-003.
Ice forming characteristics on any given cooling tower will vary, depending on velocity
and direction of wind, circulating water rate, and heat load. Excessive ice formation
may be controlled by regulating air and water flow through the tower by one or more
of the following procedures:
1– Shut the fan down. This reduces the cooling air rate to a minimum and increases
the quantity of warm water at the air inlet to a maximum. However, normal “fan off”
operation causes reverse air flow by aspiration and may cause water blowout and
therefore must be done with caution and monitoring. For automatic operation, a timer
switch can be provided to shut the fan down for a few minutes each hour.
2– When a cooling tower has two-speed motors, operate the fans at half speed forward.
This reduces the cooling air rate (heat transfer) and increases the quantity of warm
water at the air inlet.
Not recommended for plume control.
3– With no heat load on the circulating water, icing cannot be controlled. Towers
must
not
be operated with reduced water rate and/or no heat load during freezing weather.
If a bypass directly into the cold water basin is used, all water must be bypassed.
Reverse operation of fans is not recommended . See “Fan Drive” for fan speed
change precautions.
INTERMITTENT OPERATION
–When the unit is operated intermittently during win-
ter weather, it is necessary that the water be drained from the tower piping to insure
protection against freezing and possible rupture.
Caution
operation