SPX Cooling Technologies Marley MH 05-116E - Manual (Page 18)

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Reversal may be at either full or half speed; however, reversal at half
speed is recommended. 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. Monitor-
ing 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.
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 and pump
freeze protection systems available from Marley.
Basin heaters systems will not prevent the coil from freezing.
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.
Protection against Coil Freezing:
Ethylene and propylene glycol solutions are the best means to protect the
coil from freezing. The following table provides the coil volume for each
MH Fluid Cooler model. MHF706 and MHF707 coil volumes are for both
coils added together.
Operation
Warning
Warning
Warning
Caution