Calculators
Cooling Water Makeup & Cycles of Concentration
Open-recirculating cooling tower water balance. Computes evaporation, drift, blowdown, and makeup from circulating flow, range ΔT, drift rate, and target cycles of concentration. Returns circulating-water TDS, annual makeup, heat rejected, and a control-line check on COC vs makeup chemistry per CTI ATC-105 and Perry’s Chapter 12.
Method: Mass balance on a steady-state evaporative tower with conservative dissolved solids. Evaporation E = Q·ΔT·k where k ≈ 0.001 / °F for a typical counterflow tower (CTI ATC-105 approximation, range 0.0008–0.0012). Drift D = Q·fdrift. TDS balance gives blowdown B = E/(COC−1) − D and makeup M = E + D + B. Circulating TDS = TDSmakeup·COC. Annual makeup converts GPM × 60 × 24 × 365 / 1000 to kgal/yr. Heat rejected = Q·8.33 · 60 · ΔT / 106 (MMBtu/hr) using Cp = 1 BTU/lb-°F. Validation: COC > 1, B ≥ 0 (if negative, drift alone exceeds the COC target — reduce drift or raise COC), and check circulating chemistry against scaling limits (typ. silica < 150 mg/L, total hardness < 500 mg/L CaCO3, chloride < 200–300 mg/L for SS316). References: CTI ATC-105 Acceptance Test Code for Water Cooling Towers; Perry’s Chemical Engineers’ Handbook 9th Ed., Ch. 12; Nalco Water Handbook 3rd Ed. (Flynn); NACE SP0199 Cooling Water Treatment; ASME PTC 23.
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