Calculator inputs
Formula used
This calculator estimates cooling tower size from circulation flow, entering and leaving water temperatures, and the site wet bulb temperature. The main heat balance uses the sensible heat removed from water.
| Calculation | Formula |
|---|---|
| Range | Range = Hot Water Temperature − Cold Water Temperature |
| Approach | Approach = Cold Water Temperature − Wet Bulb Temperature |
| Heat rejection | Q (kW) = ρ × Flow (m³/h) ÷ 3.6 × Cp × Range |
| Tower capacity | Tower Tons = Q ÷ 3.517 |
| Effectiveness | Effectiveness = Range ÷ (Range + Approach) × 100 |
| Evaporation loss | Evaporation (gpm) = 0.00085 × Circulation (gpm) × Range (°F) |
| Blowdown | Blowdown = Evaporation ÷ (Cycles of Concentration − 1) |
| Make-up water | Make-up = Evaporation + Drift + Blowdown |
| Estimated cells | Cells = Ceiling(Design Tower Tons ÷ Cell Capacity) |
Assumed constants: water density ≈ 1000 kg/m³ and specific heat ≈ 4.186 kJ/kg·K.
How to use this calculator
- Enter the circulation flow rate for the condenser or process loop.
- Add the hot water temperature returning to the tower.
- Add the desired cold water temperature leaving the tower.
- Enter the design entering wet bulb temperature for the project location.
- Set cycles of concentration and drift percentage for water management.
- Enter a design margin, cell capacity, fan power, and basin retention time.
- Click the calculate button to show the result block below the header.
- Review tower tons, cells, water losses, and the Plotly chart. Use the export buttons for reports.
Example data table
| Scenario | Flow (m³/h) | Hot Temp (°C) | Cold Temp (°C) | Wet Bulb (°C) | Range (°C) | Design Tons | Cells | Make-up (m³/h) |
|---|---|---|---|---|---|---|---|---|
| Sample A | 250 | 37 | 29 | 25 | 8 | 727.34 | 2 | 4.128 |
| Sample B | 320 | 38 | 30 | 26 | 8 | 930.99 | 3 | 5.284 |
| Sample C | 180 | 35 | 28 | 24 | 7 | 467.32 | 2 | 2.365 |
FAQs
1. What does cooling tower sizing mean?
Cooling tower sizing estimates the tower capacity needed to reject heat from circulating water. It also helps predict approach, range, water losses, and the likely number of tower cells required for a practical construction design.
2. Why is wet bulb temperature important?
Wet bulb temperature represents the practical lower limit for tower cooling. A lower wet bulb usually allows colder leaving water. The approach value compares your target cold water temperature against this outdoor design condition.
3. What is the difference between range and approach?
Range is the temperature drop across the tower, from hot water in to cold water out. Approach is the gap between cold water temperature and entering wet bulb temperature. Both values strongly affect tower performance and size.
4. Why does the calculator include design margin?
Design margin adds reserve capacity above the calculated base load. This can help account for fouling, weather variation, future process changes, and uncertainty during early construction planning or equipment selection.
5. What are evaporation, drift, and blowdown?
Evaporation is water lost during heat rejection. Drift is tiny droplets carried away with the air stream. Blowdown is water intentionally discharged to control dissolved solids. Together, they define make-up water demand.
6. How accurate is the estimated cell count?
The cell count is a planning estimate based on the typical capacity you enter. Final selection depends on manufacturer data, fan configuration, fill performance, altitude, noise limits, and project-specific construction constraints.
7. Can I use this for HVAC and industrial projects?
Yes. The page works for condenser water systems, plant cooling loops, and process applications. Still, you should validate final tower selection with vendor performance curves and the full mechanical design basis.
8. When should I confirm results with a manufacturer?
Confirm results whenever the project is moving into procurement, detailed engineering, or permit review. Manufacturer selection software can account for exact fills, fan power, altitude, materials, and guaranteed thermal performance.