Use this construction-focused calculator to estimate cooling tower approach, range, effectiveness, and optional heat rejection from field temperatures and flow.
Calculator Inputs
Example Data Table
| Case | Hot Water (°C) | Cold Water (°C) | Wet Bulb (°C) | Approach (°C) | Range (°C) | Effectiveness (%) |
|---|---|---|---|---|---|---|
| Commissioning A | 35 | 29 | 26 | 3 | 6 | 66.67 |
| Commissioning B | 37 | 30 | 27 | 3 | 7 | 70.00 |
| Peak Load | 40 | 32 | 28 | 4 | 8 | 66.67 |
| Warm Afternoon | 42 | 33 | 29 | 4 | 9 | 69.23 |
Formula Used
1) Cooling Tower Approach
Approach = Cold Water Temperature − Ambient Wet Bulb Temperature
2) Cooling Tower Range
Range = Hot Water Temperature − Cold Water Temperature
3) Tower Effectiveness
Effectiveness = Range ÷ (Range + Approach) × 100
4) Heat Rejection
Heat Rejection (kW) = Mass Flow × 4.186 × Range in °C
These equations help evaluate how closely the tower cools water toward ambient wet bulb conditions and how much thermal load the tower rejects.
How to Use This Calculator
- Enter the hot water temperature arriving at the cooling tower.
- Enter the cold water temperature leaving the tower basin.
- Enter the ambient wet bulb temperature measured near the tower air inlet.
- Choose the temperature unit used for all temperature values.
- Add design approach and design range to compare actual versus expected performance.
- Optionally add circulating water flow and fan power for thermal duty and specific fan power.
- Press the calculate button to display the result block above the form.
- Use the chart and download buttons to document field checks.
FAQs
1) What is cooling tower approach?
Cooling tower approach is the difference between cold water leaving the tower and ambient wet bulb temperature. A smaller approach usually means the tower is cooling water closer to the theoretical atmospheric limit.
2) What is the difference between approach and range?
Approach compares outlet water to wet bulb temperature. Range compares inlet hot water to outlet cold water. Approach measures how close the tower gets to ambient potential, while range measures how much cooling occurs through the tower.
3) Why is wet bulb temperature used instead of dry bulb?
Cooling towers reject heat mainly through evaporation. Wet bulb temperature reflects the air’s evaporative cooling potential better than dry bulb temperature, so it is the proper reference for tower approach and effectiveness calculations.
4) Is a lower approach always better?
Usually yes, but lower approach often requires more tower size, airflow, or energy. Performance must be judged against design conditions, fan power, water flow, and operating cost rather than approach alone.
5) Can I use Fahrenheit values in this calculator?
Yes. Select Fahrenheit and enter all temperatures in the same unit. The calculator keeps the main result in your chosen unit and also shows converted temperature differences for convenience.
6) Why does the calculator show unusual effectiveness values?
Effectiveness can become negative or exceed 100% when temperatures are inconsistent, sensors are incorrect, or readings were taken during unstable conditions. Recheck hot water, cold water, and wet bulb measurements first.
7) How does water flow affect heat rejection?
Heat rejection depends on both water flow and cooling range. Higher flow or greater range increases the thermal duty. That is why two towers with the same approach may still reject different total heat loads.
8) When should I compare actual and design approach?
Compare actual and design approach during commissioning, troubleshooting, seasonal reviews, fill inspection, fan performance checks, and condenser water optimization. It helps identify fouling, airflow issues, and off-design operation quickly.