Operating Cooling Towers in Freezing Weather

During Winter operation, a cooling tower brings as much low temperature air into contact with the flowing water as the tower fan(s) will permit. The greater the flow of cold air, the colder the water temperature will become. Fortunately, when under design process heat loads, the temperature gradients that naturally occur in counterflow cooling towers (All Delta designs) prevent the mass flow of water from reaching 32 F. 

Cooling tower water will freeze very reluctantly and usually with advance warning. In reality, the opportunity for destructive ice is remote. It is only when droplets or minor streams of water escape the mainstream that they are subject to the full effect of the cold air and can become a steadily building mound of ice.

Here are some basic operating rules that should be followed for cooling tower operation in cold weather: 

  • Insure that the cooling tower is operating at the MAXIMUM POSSIBLE HEAT LOAD. An operating cooling tower will continuously extract heat from the circulating water. Without a heat load, the water will end up either at the air wet bulb temperature or as ice, whichever comes first. 
  • Maintain designed water flow rate over the fill. Reducing water flow over the fill area can produce semi-dry regions that are subject to rapid freezing. 
  • Make sure a thermostat is installed to control fan operation to off at lower cold water temperatures.
  • If the tower is equipped with a VFD or two speed motors, operate at a reduced or low speed to  increase water temperature leaving the cooling tower.
  • Check cycle fans periodically to prevent ice from forming on louvers.
  • It may be necessary to reverse fans a short period of time to melt ice by forcing warm water into the tower.
  • Frequent visual inspection and routine maintenance during sub-freezing operation is very important and should  not be overlooked. 
  • If ice build up occurs, use caution when removing the ice to prevent tower damage or injury to the employee. 
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