Why is my cooling tower approach increasing?

Range and approach

Range is the difference between hot water entering and cold water leaving the tower. Approach is the difference between cold water leaving and the ambient wet-bulb temperature. A tower can never cool water below wet bulb, so approach is the honest measure of tower health. Typical design approach is 3–5 °C.

Always measure wet bulb at the time of the test. On a humid monsoon day the cold-water temperature will rise even if the tower is perfect. Our Professional Converter shows live wet bulb for your city, which makes this check quick.

Common causes

• Clogged or collapsed fill media reduces the water surface in contact with air
• Blocked or missing spray nozzles create dry zones and channelling
• Fan blade pitch reduced, belt slipping or gearbox issues lower airflow
• Hot-water flow above design overloads the tower
• Drift eliminators damaged, allowing bypass of air
• Nearby walls or other equipment causing warm air recirculation

Restoring performance

Shut down one cell at a time, inspect the distribution deck and replace broken nozzles. Lift a few fill packs to check for scale or algae. Measure fan motor current: a low current at the correct speed suggests low blade pitch. A good water-treatment programme — controlled blowdown based on conductivity, a scale inhibitor and a biocide — prevents most fill problems from returning.