Calculate cooling tower cycles of concentration from system and makeup conductivity, or solve either conductivity value from the other two.
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Cooling Tower Cycles of Concentration Formula
The cooling tower cycles of concentration is the ratio of the recirculating system water conductivity to the makeup water conductivity. Both conductivity values must be in the same unit before dividing.
COC = C_s / C_m
- COC = cooling tower cycles of concentration, unitless
- C_s = conductivity of system water
- C_m = conductivity of makeup water
The same relationship can be rearranged to solve for either conductivity value:
C_s = C_m * COC
C_m = C_s / COC
The calculator supports three functions:
- Find cycles of concentration: enter system conductivity and makeup conductivity. The calculator divides system conductivity by makeup conductivity.
- Find system conductivity: enter makeup conductivity and cycles. The calculator multiplies makeup conductivity by cycles.
- Find makeup conductivity: enter system conductivity and cycles. The calculator divides system conductivity by cycles.
Conductivity inputs can be entered in µS/cm, mS/cm, or S/m. The calculation converts conductivity values to the same base unit before applying the formula.
Conductivity Unit Conversions for Cooling Tower Calculations
| Unit | Equivalent in µS/cm | Example |
|---|---|---|
| µS/cm | 1 µS/cm | 800 µS/cm = 800 µS/cm |
| mS/cm | 1 mS/cm = 1,000 µS/cm | 2.5 mS/cm = 2,500 µS/cm |
| S/m | 1 S/m = 10,000 µS/cm | 0.3 S/m = 3,000 µS/cm |
Typical Cycles of Concentration Ranges
| Cycles of concentration | General interpretation | Common note |
|---|---|---|
| Less than 2 | Low concentration | May indicate high blowdown or low reuse of makeup water. |
| 2 to 5 | Common operating range | Often used when water chemistry and treatment limits are moderate. |
| 5 to 8 | Higher concentration | Usually requires closer control of scale, corrosion, and biological treatment. |
| Above 8 | Very high concentration | May be possible only with suitable makeup water and a controlled treatment program. |
Example Problems
Example 1: Calculate cycles of concentration
You have a cooling tower system conductivity of 2,400 µS/cm and a makeup water conductivity of 600 µS/cm.
COC = 2400 / 600 = 4
The cooling tower is operating at 4 cycles of concentration.
Example 2: Calculate system conductivity
You have makeup water conductivity of 750 µS/cm and want to know the system conductivity at 5 cycles of concentration.
C_s = 750 * 5 = 3750 µS/cm
The expected system conductivity is 3,750 µS/cm.
FAQ
What are cycles of concentration in a cooling tower?
Cycles of concentration show how concentrated dissolved solids have become in the recirculating cooling tower water compared with the makeup water. If the system water has four times the conductivity of the makeup water, the tower is at 4 cycles.
Why is conductivity used to estimate cycles of concentration?
Conductivity rises as dissolved ions build up in the tower water. Since evaporation removes mostly pure water and leaves dissolved solids behind, conductivity is a practical field measurement for estimating concentration. The method works best when the same conductivity basis is used for both system and makeup water.
Can cycles of concentration be too high?
Yes. Higher cycles reduce blowdown water use, but they also increase dissolved solids. If cycles are too high for the makeup water quality and treatment program, scale, corrosion, fouling, or biological issues can increase. The acceptable value depends on water chemistry, equipment, operating temperature, and treatment limits.
