How to use Industrial Cooling Tower Evaporation, Drift& Makeup Water Calculator
- Enter Circulating water rated flow rate Q (m³/h) and adjust the options as needed.
- Run the tool and inspect its results, evidence and limitations.
- Copy or download the result, then verify it against the actual website, source data or business records.
Try a concrete example
Flow 500 m³/h, water temperatures 37°C/32°C (Range = 5.0°C), wet-bulb 28°C (Approach = 4.0°C), COC = 4.0, drift 0.005%: heat rejection is 2908 kW (827 US RT / 746 CTT). Hourly evaporation E = 3.825 m³/h, drift D = 0.025 m³/h, blowdown B = 1.25 m³/h, giving total makeup M = 5.10 m³/h (1.02% of circulation). Over 6000 hrs/yr, fresh water use is 30,600 m³ ($122,400). Compared to baseline COC=2, water savings reach 15,300 m³/yr ($61,200).
How to interpret results
Cooling towers dissipate heat via latent heat of water evaporation. Sizing evaluates mass conservation M = E + D + B to optimize cycles of concentration (COC), preventing scaling while reducing blowdown and fresh water procurement expenses.
Frequently asked questions
What is the engineering distinction between cooling tower Range and Approach?
Range (ΔT = Th - Tc) is determined entirely by process heat load and water flow, typically 5°C (37°C/32°C for HVAC) to 10°C (heavy industry). Approach (Tc - Twb) represents how closely cold water temperature approaches ambient wet-bulb temperature. Smaller approaches require exponentially larger tower fill volumes; 3.0~5.0°C is standard, while approaches below 2.5°C are rarely cost-effective.
How is Cycles of Concentration (COC) defined, and why is it critical for water conservation?
COC is the ratio of dissolved solids (TDS) in circulating water to that in fresh makeup. Blowdown B = (E - (COC-1)×D) / (COC-1). Raising COC from 2.0 to 4.0 cuts required blowdown by 66% and fresh makeup by over 30%. Operating above COC 5.0 yields diminishing returns while risking severe calcium carbonate and silica scaling.
What are international drift loss standards, and why must Legionella risk be mitigated?
Drift comprises unevaporated water droplets swept out in exhaust airflow. Legacy towers without drift eliminators lost 0.1%~0.2%, creating major Legionella pneumophila aerosol transmission risks. CTI standards mandate cellular drift eliminators to restrict drift below 0.005%~0.001% of circulating flow.
How is cooling tower hourly evaporation loss E calculated accurately?
Evaporative cooling relies on water latent heat of vaporization (r ~ 2450 kJ/kg = 0.68 kWh/kg) versus sensible cooling (4.186 kJ/kg·°C). Cooling 1 kg of water by 1°C requires evaporating ~0.00171 kg. Accounting for ~15% sensible heat exchange by airflow, the CTI/Marley empirical constant is 0.00153~0.0016/°C (E = 0.00153 × Q × ΔT).