Commonly, the size of a tower is identified by thediameter of the fan. Fan sizes range from 7 to 42 ft,with the most common applications in the 16–24-ft range. The speed of the fan is limited by the mechanical stress on the fan blades. Typical fan speeds are in the range of 125–300 r/min. The horsepower of the motorrequired to drive the fan at the desired speed is calculatedbased on the air volume required. (Table 1 shows )horsepower ratings for cooling towers located at a typical petrochemical plant.