Circulating Water Parameter Conversion — A One-Stop Guide

Circulating water parameter conversion is a closed-loop logic from basic flow balance, to water stability assessment, to precise chemical control. Mastering this method helps operators accurately judge the system status and provides a reliable basis for chemical dosing and water quality management.

1. The basic flow balance equation

In industrial cooling water circuits, water losses include evaporation loss E, windage / drift loss W and blowdown loss B. The make-up water M must compensate all three to keep the balance.

M = E + W + B

Engineering estimate of evaporation E:

E ≈ 0.001 × ΔT × Q_circ (unit: m³/h)

ΔT is the temperature difference across the cooling tower (°C), Q_circ is the circulating flow rate (m³/h).

2. Cycles of concentration N — calculation & meaning

Cycles of Concentration (N) is the core control parameter in a cooling loop, indicating scaling and corrosion tendency.

N = C_circ / C_make-up = (E + W + B) / (W + B)

Common tracers: chloride or conductivity

Chloride method: stable and not interfered with by chemicals—recommended first choice.
Conductivity method: quick to measure on-site, but affected by chemical additives.

Cycles N	Water saving	Scaling / corrosion tendency	Recommended use
2.0	~50%	Low	Poor source water, high hardness
3.0	~67%	Medium	Typical industrial cooling
4.0–5.0	75–80%	Higher	Good source water + high-performance scale inhibitor
≥ 6.0	>83%	High	Premium scale/dispersant + strict monitoring

3. Converting blowdown B

With evaporation E and drift W known, blowdown B can be derived from the target N:

B = E / (N − 1) − W

Windage W is typically 0.05%–0.3% of Q_circ for mechanical-draft cooling towers; larger towers can be lower.

4. Precise calculation of chemical dosing

Two common dosing strategies are used in cooling loops:

1) By make-up water (typical for scale inhibitors)

G_chem (kg/h) = M × C_dose × 10⁻³

C_dose is the dosing concentration (mg/L or ppm), M is make-up water (m³/h).

2) By total system holding volume (shock dosing for biocides)

G_chem (kg) = V_system × C_dose × 10⁻³

V_system is the total holding volume of the cooling system (m³), including tower basin, piping, heat exchangers and sumps.

5. Daily operating conversion chain

Use ΔT across the tower → estimate evaporation E.
Measure Cl⁻ or conductivity → calculate cycles of concentration N.
With target N and drift W → derive reasonable blowdown B.
Combine E, W, B → get the actual make-up demand M.
With M and formula C_dose → set the chemical pump dosing rate.

Operating tip: We recommend plants log circulating and make-up water conductivity, Cl⁻ and pH every 4 hours and auto-calculate N together with blowdown valve opening. The Aqua-Link smart O&M platform can stream these inputs in real time and interlock with TRISPE® scale inhibitor and PT-BIO® biocide dosing pumps to optimize cycles of concentration and chemical consumption automatically.

6. Summary

The core of circulating water parameter conversion is to build quantitative relationships among five variables: make-up, evaporation, blowdown, cycles of concentration and chemical consumption. Mastering them allows operators to:

Judge whether the system is at the optimal water-saving / stable / low-corrosion balance point;
Quickly identify whether scaling / corrosion anomalies stem from flow imbalance or chemical failure;
Save 10%–25% of total water treatment cost per year.

If your plant needs parameter conversion and optimization diagnostics for an existing cooling system, contact the Aqua-Link technical team for a free proposal.

Technical Article