What this calculator finds

From the hot-water inlet temperature, the cold-water outlet temperature, and the ambient wet-bulb temperature, it computes Range, Approach, and Effectiveness. Range is the temperature drop the tower actually achieves, while Approach shows how close the cold water gets to its theoretical limit (the wet-bulb temperature).

Why it matters

• Diagnosing whether an operating tower is holding its design performance
• Identifying causes of degradation such as fouled fill or insufficient air flow
• Confirming the cold-water temperature needed for chiller or process efficiency

Cooling Tower Performance Formulas

The three metrics are defined by simple differences and a ratio of the three temperatures, with the wet-bulb temperature acting as the theoretical cooling limit.

How the formulas work

• A larger Range means the tower removed more heat; it is governed by the circulating-water flow and the heat load.
• A smaller Approach (cold water closer to the wet-bulb) indicates better performance; Approach can never reach zero.
• Effectiveness is the achieved cooling (Range) divided by the theoretical maximum (Range + Approach); closer to 100% is ideal.

Worked example

For T_hw = 37°C, T_cw = 32°C, T_wb = 27°C: Range = 37 − 32 = 5°C, Approach = 32 − 27 = 5°C, and Effectiveness = 5 / (5 + 5) × 100% = 50%.

Practical tips

• The wet-bulb temperature reflects humidity, not dry-bulb; use a hygrometer or psychrometer for accurate readings.
• Design Approach is typically 3–5°C; a rising Approach points to fouled fill or reduced air flow.
• A low Range may reflect changes in circulating flow or heat load rather than the tower itself.

Limitations & cautions

• These metrics summarize performance from temperature differences, not the detailed heat/mass-transfer mechanism.
• The wet-bulb temperature is the theoretical floor — cold water can never be cooled below it.
• Make-up water and concentration cycles from evaporation, drift, and blowdown must be managed separately.