Cooling Tower Water loss Calculator



Cooling towers are used to dissipate heat from industrial processes or HVAC systems by transferring heat from the process fluid (usually water) to the atmosphere. In cooling towers, water loss occurs mainly through evaporation, drift, and blowdown. Here's a simple method to estimate water loss in a cooling tower:

You will need the following information:

  1. Cooling tower capacity (Q) in kilowatts (kW)
  2. Range of the cooling tower (ΔT) in degrees Celsius (°C)
  3. Cycles of concentration (COC)
  4. Drift loss rate (D) as a percentage of circulating water flow
  5. Cooling tower efficiency (η) - usually between 0.7 and 0.85

Step 1: Calculate the evaporation loss (E): Evaporation loss (E) is the amount of water that evaporates as the cooling tower dissipates heat.

E = Q * 1.8 / (η * ΔT)


  • E = evaporation loss in liters per hour (L/h)
  • Q = cooling tower capacity in kW
  • η = cooling tower efficiency (dimensionless)
  • ΔT = range of the cooling tower in °C

Step 2: Calculate the drift loss (Drift): Drift loss (Drift) is the amount of water carried out of the cooling tower by air movement.

Drift = (Circulating water flow * D) / 100


  • Drift = drift loss in liters per hour (L/h)
  • Circulating water flow = E * (COC + 1) / COC
  • D = drift loss rate as a percentage

Step 3: Calculate the blowdown loss (B): Blowdown loss (B) is the amount of water removed from the system to maintain the desired concentration of dissolved solids in the cooling tower water.

B = E / (COC - 1)


  • B = blowdown loss in liters per hour (L/h)
  • E = evaporation loss in L/h
  • COC = cycles of concentration

Step 4: Calculate the total water loss (Total_Loss): Total water loss is the sum of evaporation loss, drift loss, and blowdown loss.

Total_Loss = E + Drift + B

The result, Total_Loss, will give you an estimate of the cooling tower water loss in liters per hour (L/h). Note that these calculations are approximate, and actual water loss may vary depending on various factors, such as the cooling tower design, operating conditions, and local climate.

Calculation Preview

25 Apr 2023
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File Version: 1.0
File Author: Michael Haise
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Comments: 1
johndoyle[admin] 4 years ago
Lifetime free subscription well earned Michael!
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