Cooling Tower Blowdown Calculator
Total system flow rate in gallons per minute.
Difference between hot return and cold supply water.
Target concentration ratio (must be > 1.0).
Standard (0.1% per 1°F)
High Efficiency (0.085%)
Rule of thumb constant for calculation.
Calculated Evaporation (E):
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Total Makeup Water (M):
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Required Blowdown Rate (B):
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Water Efficiency:
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Understanding Cooling Tower Blowdown
In industrial cooling systems, managing the water balance is critical for preventing scale accumulation, corrosion, and biological growth. As pure water evaporates from the tower to provide cooling, dissolved solids (like calcium, magnesium, and silica) remain behind in the recirculating water. If not managed, the concentration of these solids increases indefinitely.
Blowdown (or bleed-off) is the intentional removal of a portion of this concentrated water to be replaced by fresh makeup water. This calculator helps operators determine the precise flow rate required to maintain a specific "Cycle of Concentration."
Key Formulas
This tool utilizes standard mass balance equations used in water treatment engineering:
- Evaporation (E): Estimated as Recirculation Rate × ΔT × Factor. A common rule of thumb is that 0.1% of the circulation rate evaporates for every 1°F drop in temperature.
- Blowdown (B): Calculated using the formula:
B = E / (COC - 1) - Makeup Water (M): The total fresh water required:
M = E + B(ignoring drift loss, which is usually negligible).
What are Cycles of Concentration?
Cycles of Concentration (COC) represents the ratio of the concentration of dissolved solids in the blowdown water to the makeup water. Higher cycles mean less water usage (lower blowdown) but increase the risk of scale formation.
- Low COC (e.g., 2-3): High water consumption, low scaling risk. Often indicates inefficient chemical treatment.
- High COC (e.g., 6-10): Water efficient, but requires precise chemical control and high-quality makeup water.
Use this calculator to optimize your water treatment program and ensure your cooling tower operates efficiently without wasting water or damaging equipment.