▲Caution
▲Caution
▲Caution
Freezing Weather Operation
•Under extended extreme cold conditions, it may be necessary to operate the fan in reverse. This forces warm air out through the air inlets, melt- ing any accumulated ice. Reversal may be at either full or half speed; however, full speed is recommended if adequate heat load is available. Reverse operation of the fan should be avoided, where possible, and should not exceed 15 to 20 minutes.
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. Reverse opera- tion of fans with adjacent fans not operating increases probability of icing. The low discharge velocity of moist air from fan cylinders in which fans are not in operation can result in
•With no heat load on the circulating water, icing cannot be controlled effectively by air control alone during freezing weather. Towers must not be operated with reduced water rate and/or no heat load during freez- ing weather. If a bypass directly into the cold water basin is used, all water must be bypassed. Water flow over the tower must never be modulated during freezing weather.
See Fan Drive on pages 9 and 10 for fan speed change and reversing precautions.
Intermittent Operation
When the unit is operated intermittently during winter weather, it is necessary that the water be drained from the tower piping to insure protection against freezing and possible rupture.
12
