Cooling Tower Evaporation Rate Calculator
Professional tool for HVAC engineers and water treatment specialists
Calculation Results
Cooling Range: 0 °F
Evaporation Rate: 0 GPM
Blowdown Rate: 0 GPM
Total Makeup Water: 0 GPM
Understanding Cooling Tower Evaporation Rate
The evaporation rate is a critical metric in cooling tower management. It represents the volume of water converted to steam to reject heat from the system. Accurate calculation helps in determining chemical dosage, water costs, and environmental compliance.
The Physics of Evaporation Calculation
While precise calculations involve complex thermodynamics (enthalpy of air), the industry standard uses a simplified formula based on the cooling range (the difference between the inlet and outlet water temperatures).
- Imperial Formula: E = Q × Range × 0.0008
- Metric Formula: E = Q × Range × 0.00153
Where Q is the flow rate and Range is the temperature drop. The factor 0.0008 (Imperial) assumes that for every 10°F of cooling, approximately 0.8% to 1% of the water is evaporated.
Key Variables Explained
Cycles of Concentration (COC): This is the ratio of dissolved solids in the tower water to those in the makeup water. Higher COC saves water but increases the risk of scaling and corrosion. It is used to calculate Blowdown (the water intentionally drained to remove concentrated solids).
Total Makeup Water: This is the sum of Evaporation, Blowdown, and Drift loss. It represents the total amount of fresh water your facility must supply to the cooling tower.
Practical Example
Suppose you have a cooling tower operating at 1,000 GPM. The hot water enters at 95°F and leaves at 85°F (Range = 10°F). If your COC is set to 4.0:
- Evaporation: 1,000 × 10 × 0.0008 = 8 GPM
- Blowdown: 8 / (4.0 – 1) = 2.67 GPM
- Makeup Water: 8 + 2.67 = 10.67 GPM