Winter Operation - Baltimore Aircoil Company 3000 Series Operating And Maintenance Instructions Manual

Winter Operation

he Series 3000 and Series 1500 Cooling Towers
T
can be operated at ambient temperatures below
freezing provided proper operating methods are
established and diligently followed. Precautions that must
be taken to insure satisfactory operation include:
• Freeze protection of the water in the cold water basin
when tower is idle.
• Elimination of water in the optional BALANCE CLEAN
Chamber and internal piping (Series 3000 only) when
the tower is idle.
• Elimination of water in the optional EASY CLEAN
Chamber and internal piping (Series 1500 only) when
the tower is idle.
• Control of ice formation during tower operation.
Freeze protection must be provided for the cold water
basin during shutdown since ice formation in the basin
can severely damage the cooling tower. A remote sump
located indoors in a heated space is an ideal method
since the water in the tower and connecting piping will
drain by gravity whenever the circulating pump is
stopped. Where a remote sump arrangement is
impractical, a form of cold water basin heat must be
provided in the tower itself. Electric immersion heaters
or steam coils, controlled by a thermostat in the cold
water basin, may be used. Consult your B.A.C.
Representative for details. Additionally, where a remote
sump is not used, all exposed make-up lines and
water piping that does not drain at shutdown should
be traced with electric heater tape and insulated.
Series 3000 Cooling Towers with Optional BALANCE-
CLEAN ® Chamber or Series 1500 Cooling Towers with
Optional EASY-CLEAN™ Chamber
Draining the water from the BALANCE CLEAN
EASY-CLEAN™ Chambers and internal piping is essential
whenever the potential for freezing temperatures exist.
This can be accomplished by utilizing the 1/2" NPT port
drain located on the inboard side of the BALANCE
CLEAN ® or EASY-CLEAN™ Chamber. There are 3
recommended methods for draining the piping:
1. The preferred approach is to install a normally open
1/2" solenoid valve on the 1/2" drain connection of the
BALANCE CLEAN ® or EASY-CLEAN™ Chamber. This
valve should be wired in the pump circuit such that it
closes when the pump is energized. The solenoid valve
must be selected to operate with a minimum pressure
differential of zero psi. The zero pressure differential valve
is required due to the limited static head imposed on the
valve from the water column.
or
2. A 1/2" manual valve can be installed on the 1/2" drain
connection of the BALANCE CLEAN
Chamber. The valve should be opened during cold
weather operation. CAUTION: The valve must be closed
during warm weather to obtain full thermal performance.
®
®
® or
® or EASY-CLEAN™
or
3. Remove the 1/2" plug from the 1/2" drain connection of
the BALANCE CLEAN ® or EASY-CLEAN™ Chamber during
cold weather operation. CAUTION: The plug must be
reinstalled during warm weather to obtain full thermal
performance.
When the cooling tower is operated at wet bulb tempera-
tures below freezing, ice may form on wetted areas in
direct contact with the incoming air. Therefore, the inlet
louvers and outer face of the wet deck surface must be
inspected frequently so that if icing occurs, steps can be
taken to remove the ice before the tower is damaged or
system performance impaired.
When operating at subfreezing ambient temperatures, the
cooling tower will normally produce leaving water temper-
atures appreciably below design. However, low leaving-
water temperatures tend to promote ice formation.
Therefore, when operating in subfreezing ambient
temperatures, the leaving water temperatures should
be maintained as high as possible. The recommended
minimum water temperature in the cold water basin is
43˚F. Additionally, frequent visual inspections should
be performed to detect potential icing problems.
The first step in maintaining a high leaving water tempera-
ture is to ensure the tower operates with the maximum
possible heat load. Next, reduce the tower capacity by
cycling fans. Modulating the water flow rate to the tower is
not recommended as a method for cooling tower capacity
control. (CAUTION: Rapid on-off cycling can cause the
fan motor to overheat. It is recommended that controls
be set to allow a maximum of 6 on-off cycles per hour.)
If the tower is equipped with two-speed motors, operation
at low speed may be sufficient to prevent icing.
(Note: When two speed motors are used, the motor
starter should include a 15 second time delay when
switching from high to low speed.) However, it may also
be necessary to cycle fans off periodically to prevent ice
formation and/or to melt ice that accumulates on the
intake louvers and face of the wet deck surface. Again, it is
recommended that the controls be set to allow a
maximum of 6 on-off cycles per hour.
Under severe conditions where fan cycling is insufficient to
prevent icing, it may be necessary to operate the fan(s) in
reverse to remove any ice accumulation by forcing warm
air out to the intake louvers. WARNING: At such times,
DO NOT operate the fans in reverse any longer than is
necessary since extended reverse operation may
cause ice to form on the fan blades, fan stack, or elimi-
nators and damage the tower. Because of this possibility,
cooling towers using reverse fan operation for ice removal
should be equipped with a vibration cutout switch and
the duration of reverse operation should be limited to a
maximum of thirty minutes. A time delay of approximately
40 seconds between forward and reverse direction should
be incorporated into the motor controls.
Lastly, the importance of performing frequent visual
inspections and routine maintenance services during oper-
ation in subfreezing weather cannot be overemphasized.
These must be carried out on a routine basis to:
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