SPX Cooling Technologies Cooling Tower Marley MD - Manual (Page 18)

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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.
Reverse operation of fans for prolonged periods during subfreezing
weather can cause severe damage to fans and fan cylinders. Ice can
accumulate inside fan cylinders at fan blade plane of rotation and
fan blade tips will eventually strike this ring of ice, damaging the fan
blades or cylinder. Ice can also accumulate on fan blades and be
thrown off, damaging fan cylinder or blades. Allow a minimum of 10
minute delay between reverse operation and forward operation during
subfreezing weather to permit ice to dissipate from fan blades and
fan cylinders. See Fan Drive Caution note on page 12 for fan speed
change and reversing precautions.
3. With no heat load on the circulating water, icing cannot be controlled
effectively by air control during freezing weather. Towers must not be
operated with reduced water rate and/or no heat load during freezing
weather. If the circulating water system cannot be shut down, water
returning from the process should be made to bypass the tower. If a
bypass is used,
all water must be bypassed without modulation. If the
water bypass is directly into the tower's cold water basin, its design
must be approved by SPX Cooling Technologies.
Intermittent Wintertime Operation:
If periods of shutdown (nights, weekends, etc.) occur during freezing
weather, measures must be taken to prevent the water in the cold water
basin—and all exposed pipework—from freezing. Several methods are
used to combat this, including automatic basin heater systems available
from Marley.
Unless some means of freeze prevention is incorporated into your
system, the tower basin and exposed pipework should be drained at
the beginning of each wintertime shutdown period.
If tower basin is drained, verify that all basin heaters have been shut
off either by automatic cutoff or disconnect switch.
It is recommended that you discuss your freeze prevention options with
your local Marley sales representative.
Warning
Operation