Potential for Ice
Factors that influence the method of ice control selected include the type of tower, the type of fill used, the water distribution system design and the mechanical equipment arrangements.
Although the methods of ice control vary somewhat - influencing factors include the type of tower, the type of fill used, the water distribution system design and the mechanical equipment arrangements - they are all based upon the following points of logic:
The potential for ice varies inversely with outside air temperatures. The lower temperatures become below freezing, the greater the probability of ice.
Within design limits, the potential for ice varies inversely with the amount of water flowing over the fill. A reduced water flow rate increases the probability of ice.
The potential for ice varies directly with the quantity of air flowing through the tower. Reducing the airflow retards the formation of ice.
Where airflow is uncontrolled (and even increasing with colder temperature, as in the case of natural-draft towers), the potential for ice formation varies inversely with the heat load imposed on the tower. In that case, a reduced heat load will increase the probability of ice.
Where airflow is controlled to maintain a specific cold-water temperature, the potential for ice varies directly with head load, and inversely with the selected cold-water temperature. Increasing the heat load, or lowering the required cold-water temperature, will increase the probability of ice.
All mechanical-draft towers permit some degree of airflow manipulation for controlling ice. The extent depends primarily upon the number of cooling tower cells and the speed-change characteristics of the motors. Larger towers designed to be operated in cold climates usually also include means by which to control placement of water over the fill. In mechanical-draft towers, airside and waterside control arrangements can be mutually supportive. However, natural-draft towers offer no reasonable opportunity for airside control.