20-15: Thermal Performance Comparison between Fan Staging and Variable Speed

The thermal performance of a cooling tower can be regulated by varying fan power. Typically, it is possible to lower fan power significantly, while only having a minimal impact on the thermal capacity of a cooling tower. Cooling towers are designed to achieve the specified cooling capacity at the highest ambient wet bulb temperatures for the area in which it will be operated. If a cooling tower is built to achieve the design operating conditions that only occur 1% to 2% of the year, there is considerable opportunity to reduce fan energy costs the remaining 98% to 99% of the year. It is for this reason, means of controlling fan power can offer large energy savings for cooling tower owners/operators. This paper will compare thermal performance test results of two multi fan rental cooling towers of similar rated capacity, with one tower equipped with means of cycling AC direct drive fan motors off and on, and another tower equipped with variable speed EC fan motors.