Cycles of Concentration
Cycles of concentration is the ratio of dissolved solids in a cooling tower's recirculating water to that in the makeup water. It indicates how many times the water has been concentrated by evaporation before being blown down.
As a cooling tower evaporates pure water, the minerals left behind concentrate in the remaining water. Running at higher cycles saves makeup water and blowdown, but pushed too far the dissolved solids scale heat-transfer surfaces and corrode metal. Operators choose a cycles target — commonly between three and seven — based on water chemistry and treatment, balancing water conservation against the risk of fouling and corrosion.