Calculate evaporation, drift, blowdown, and makeup water balance for cooling towers, with a Langelier Saturation Index model that dynamically flags scaling and corrosion risk in the circulating water.
Evaporation, drift, blowdown and makeup water balance from mass conservation, plus Langelier Saturation Index scaling/corrosion risk screening for the circulating water.
Local Engine
Project Information
Heat Load & Water Balance
Cooling range (ΔT): —
Typical operating range: 3–6.
Default 0.00153 (metric, m³/h & °C basis) — see methodology note below. Typical range 0.00115–0.00195 for climate variation.
Circulating Water Chemistry (for LSI)
Estimate from Makeup Water Optional
If you only have makeup water lab data on hand, enter it here and estimate the concentrated circulating-water values (Ca, Alkalinity, TDS all scale × CoC at steady state). Note: pH does not scale linearly with CoC (CO2 stripping in the tower shifts the carbonate equilibrium) — estimated circulating pH typically settles between 8.2–8.8 unless acid is dosed. Enter your own circulating water pH reading above rather than scaling it.
Water Balance Results
Evaporation Loss (E)
—m³/h
E = k × Flow × ΔT
Drift Loss (D)
—m³/h
—
Blowdown Required (B)
—m³/h
B = E/(CoC−1) − D
Total Makeup Water (M)
—m³/h
M = E + D + B
Achieved CoC: —
Heat rejected (informational): —
Scaling & Corrosion Risk (LSI)
ℹ
—
Enter circulating water chemistry to evaluate scaling/corrosion risk.
Saturation pH (pHs)
—
Langelier Saturation Index
—
LSI = pH − pHs
Ryznar Stability Index
—
RSI = 2×pHs − pH
Design Notes & Warnings
Export includes the current water balance and water chemistry configuration and results.
Evaporation coefficient: the commonly cited "0.0008/0.00085 × flow × range" rule of thumb is an imperial constant (gpm, °F) — used directly against a Celsius ΔT without the required ×1.8 unit conversion it understates evaporation by roughly 1.8×. This tool defaults to the converted metric constant, 0.00153, cross-checked against the independent "~1% evaporation per 5.6°C range" industry rule of thumb.
01
Engineering Basis
Methodology
Evaporation, drift, and blowdown follow a standard mass-conservation water balance (CTI/ASHRAE convention): evaporation loss is proportional to circulating flow x cooling range, drift loss follows the selected drift eliminator performance class, and forced blowdown is solved directly from a steady-state Cycles of Concentration mass balance.
Scaling/corrosion tendency uses the Langelier Saturation Index (Langelier, 1936) computed from water temperature, pH, calcium hardness, total alkalinity, and TDS, with the Ryznar Stability Index included as a secondary cross-check — both are empirical screening indices, not a substitute for a full water treatment chemical program.
LSI and RSI are empirical screening indices; they do not replace a complete water-treatment chemical program.
CTI/ASHRAE mass-balance water balance; Langelier (1936) Saturation Index and Ryznar Stability Index for vendor-neutral scaling/corrosion risk screening.
Cooling waterA systems route from makeup-water characterization through conditioning, cooling-system balance, blowdown, and reuse or discharge context.
