12
operation
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.
Operating the fan in reverse at half speed 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 in the Mechanical Equipment Installation section of this manual.
4. 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. It is
recommended that you discuss your freeze prevention options with your local
Marley sales representative.
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.
Warning
Caution
Warning
