Cycles of concentration (COC) describe how much dissolved material has concentrated in circulating cooling water compared with make-up water. If make-up conductivity is 500 µS/cm and circulating conductivity is 2,000 µS/cm, the conductivity-based COC is approximately 4.
Simple conductivity method
COC ≈ Circulating conductivity ÷ Make-up conductivity
Example: 2,400 ÷ 600 = 4 cycles.
Why COC saves water
At higher cycles, less blowdown is required for the same evaporative load. This can reduce water consumption and wastewater generation. But the savings must be balanced against scaling, corrosion and deposit risks.
Why conductivity COC is only an estimate
Conductivity is affected by the combined ionic content of the water. Some species can precipitate, react, be added through treatment chemicals or enter from process contamination. For troubleshooting, compare several conservative ions or analytical parameters rather than relying on conductivity alone.
What limits the maximum cycles?
- Calcium hardness and alkalinity, which influence carbonate scaling.
- Silica concentration and temperature.
- Chloride and sulfate concentration, which can affect corrosion.
- Suspended solids and biological fouling.
- Metallurgy and maximum acceptable corrosion rate.
- Effectiveness of scale inhibitor, dispersant and biocide programs.
Operational approach
Set a target based on make-up analysis and treatment design, then control blowdown using a conductivity controller or another validated method. Trend make-up and circulating values so changes in source water are detected early.
Use the Ramven Cycles of Concentration Calculator for a quick conductivity-based estimate.