Cooling Tower Evaluator
A cooling tower with 10 L/s flow, 35 °C hot water, 29 °C cold water, and 27 °C wet bulb delivers 251 kW of cooling at 2 °C approach with evaporation of 155 L/h. Enter your operating conditions below to calculate cooling capacity, water balance and tower characteristic.
This tool calculates cooling capacity, approach, range, evaporation rate, drift loss, blowdown, total make-up water, concentration ratio, NTU and tower characteristic KaV/L using Merkel analysis with numerical integration.
Cooling Tower Inputs
Operating Costs
Cooling Tower Performance
| Property | Value | Unit |
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Cooling Tower Formulas
Cooling capacity:
Merkel equation (NTU):
Evaporation rate (rule of thumb):
Make-up water:
Frequently Asked Questions
What is the Merkel equation for cooling towers?
The Merkel equation relates the tower characteristic KaV/L to the integral of dT / (h_s - h_a) over the cooling range. This integral represents the NTU (Number of Transfer Units) required. It is evaluated numerically using the Chebyshev four-point method in this calculator.
What is cooling tower approach temperature?
Approach is the difference between the cold water leaving the tower and the ambient wet bulb temperature. Typical values are 3 to 8 °C. Smaller approach means the tower works harder. Below 3 °C requires a very large tower; above 8 °C may indicate an undersized unit.
How do I calculate cooling tower make-up water?
Make-up = Evaporation + Drift + Blowdown. Evaporation is approximately 1.8 L/h per kW of cooling. Drift is 0.002-0.005% of circulation flow. Blowdown = Evaporation / (Cycles - 1). This calculator computes all three components.
What is the concentration ratio and why does it matter?
Concentration ratio (cycles of concentration) is the ratio of dissolved solids in circulating water to make-up water. Higher ratios save water but increase scaling risk. Typical values are 3 to 5. It is controlled by adjusting blowdown rate.
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