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Cooling Tower Water Loss Calculator Engineering & Industrial
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Cooling Tower Water Loss Calculator

Determine cooling tower evaporation water loss (GPM), blowdown bleed rate, drift loss, total makeup water demand, and annual utility expenditures.

Tons
GPM
Total Makeup Water Demand
16.1 GPM
23,184 Gallons / day operating
Evaporation Loss
12.0 GPM
74.5% of total makeup
Blowdown Bleed-Off
4.0 GPM
To sewer / drain
Annual Water Consumed: 3.38 Million Gal / yr
Annual Water & Sewer Cost: $32,110 / year
Drift Loss to Atmosphere: 0.075 GPM (negligible)
Increasing cycles from 4.0 to 6.0 would save approximately 560,000 gallons ($5,300) per year.

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Cooling Tower Water Balance & Thermodynamics

Open cooling towers reject heat through the latent heat of vaporization of water. For every pound of water evaporated, approximately 1,000 BTU of latent heat is dissipated into the moving air stream. Because evaporated water leaves pure vapor behind, dissolved mineral salts (calcium, silica, chlorides) concentrate in the circulating basin water. Controlled blowdown (bleed) is necessary to prevent scale formation and pipe clogging.

Water Conservation Governing Formulas

  1. Evaporation Rate (GPM):
    E = 0.0008 × Flow (GPM) × Cooling Range (°F)
    Or roughly 2.4 to 3.0 GPM per 100 tons of refrigeration heat rejection.
  2. Blowdown Rate (GPM):
    B = E / (Cycles of Concentration - 1)
  3. Total Makeup Water Demand:
    M = Evaporation + Blowdown + Drift

Frequently Asked Questions

How much water does a 500-ton cooling tower evaporate per hour?

A 500-ton cooling tower operating at nominal design conditions evaporates approximately 12 GPM, which equals 720 gallons of water per operating hour.

What are Cycles of Concentration (COC) in cooling towers?

Cycles of Concentration measure the ratio of dissolved solids in the circulating tower basin water compared to the incoming raw city makeup water. Higher COC means less water is wasted to blowdown.

What limits how high Cycles of Concentration can be increased?

Water chemistry limits COC, specifically dissolved silica (which forms hard glass scale above 150-180 ppm), calcium carbonate hardness (scaling), and chlorides (causing stainless steel pitting).