17
Slushy, transitory ice forms routinely in the colder regions of the fill
at low temperature. Such ice normally has no adverse effect on tower
operation, but its appearance should be a signal to the operator to
undertake ice control procedures. It is the operator's responsibil-
ity to prevent the formation of destructive (hard) ice on the cooling
tower fill and louvers. Certain guidelines should be followed:
1. Do not allow the tower’s leaving water temperature to drop below a mini-
mum allowable level—say 36°F to 40°F. If such low temperature operation
is necessary or beneficial to your process, establish the minimum allowable
level as follows:
During the coldest days of the first winter of operation, observe whether
any ice is forming on the bottom of the fill or the louvers. If hard ice is
present on either component, you must increase the allowable cold water
temperature. If the coldest possible water is beneficial to your process, ice
of a mushy consistency can be tolerated—but routine periodic observation
is advisable.
If the minimum allowable cold water temperature is established
at or near minimum heat load, it should be safe for all operating
conditions.
Having established the minimum allowable cold water temperature,
maintaining that temperature can be accomplished by fan manipulation,
as outlined in Item 4 under Tower Operation. However, in towers of more
than one cell, where fans are manipulated sequentially, please realize
that the water temperature will be significantly lower in the cell or cells
operating at the highest fan speed than the net cold water temperature
produced by the entire tower would indicate. Wintertime operation of
multicell towers at low cold water temperature levels requires that the
operator be especially watchful.
2. Under extended extreme cold conditions, it may be necessary to operate
the fan in reverse. This forces warm air out through the louvers, melting
any accumulated ice—adequate heat load must be available. Reversal
of fan should only be done at half speed or less. Reverse operation of
the fan should be used sparingly and should only be used to control ice,
not to prevent it. Reverse fan operation should not need to exceed 1 or
2 minutes. Monitoring is required to determine the time required to melt
accumulated ice.
Note
Caution
operation
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