Calculator Inputs
Performance Graph
The graph shows water temperature reduction against the estimated heat removal progression through tower stages.
Example Data Table
| Case | Flow (gpm) | Hot Temp (°F) | Cold Temp (°F) | Wet Bulb (°F) | Range (°F) | Approx. Tons |
|---|---|---|---|---|---|---|
| Office Plant | 900 | 95 | 85 | 78 | 10 | 375.00 |
| Industrial Loop | 1500 | 100 | 85 | 77 | 15 | 937.50 |
| Process Cooling | 2200 | 105 | 86 | 79 | 19 | 1741.67 |
Formula Used
Cooling tower heat rejection: Q = Flow × 500 × Range × Density Factor
Cooling tower tonnage: Tons = Q ÷ 12,000
Range: Range = Hot Water Temperature − Cold Water Temperature
Approach: Approach = Cold Water Temperature − Wet Bulb Temperature
Evaporation loss: Evaporation = Evaporation Factor × Flow × Range
Drift loss: Drift = Flow × Drift Loss Percent ÷ 100
Blowdown: Blowdown = Evaporation ÷ (Cycles of Concentration − 1)
Makeup water: Makeup = Evaporation + Drift + Blowdown
Electrical intensity: kW/Ton = Total Motor kW ÷ Cooling Tons
The constant 500 assumes water near standard conditions in US customary units.
How to Use This Calculator
- Enter circulating water flow in gallons per minute.
- Provide hot and cold water temperatures at tower inlet and outlet.
- Enter the local entering air wet bulb temperature.
- Add fan and pump electrical loads to estimate energy intensity.
- Set cycles of concentration, drift percent, and evaporation factor.
- Press Calculate Now to display the result above the form.
- Review tonnage, approach, makeup water, and efficiency indicators.
- Export the output through CSV or PDF when needed.
Frequently Asked Questions
1. What does cooling tower tonnage represent?
Cooling tower tonnage expresses how much heat a tower removes. One cooling ton equals 12,000 BTU per hour. It helps compare tower capacity with chiller loads, process cooling demand, and circulation conditions.
2. Why is range important in tower sizing?
Range is the temperature drop across the tower. A larger range means more heat removed for the same flow rate. Because tonnage depends directly on range, even small temperature changes can strongly affect calculated capacity.
3. What is approach in cooling tower performance?
Approach measures how close the cold water temperature gets to entering wet bulb temperature. Lower approach generally indicates stronger thermal performance, though it often requires larger tower size, more airflow, or greater operating cost.
4. Why include fan and pump load?
Electrical load helps evaluate system efficiency, not just capacity. Fan and pump power together show how much energy the tower system uses per ton of cooling, which is useful for benchmarking operating performance and retrofit decisions.
5. What does makeup water include?
Makeup water replaces losses from evaporation, drift, and blowdown. Tracking it matters for water treatment, utility cost analysis, and sustainability planning. Higher range and lower concentration cycles usually increase required makeup flow.
6. Can this calculator be used for preliminary design?
Yes. It works well for preliminary checks, budgeting, and quick engineering comparisons. Final equipment selection should still consider manufacturer curves, site altitude, local climate, water chemistry, fouling allowance, and operating redundancy.
7. Why use the 500 constant?
The 500 constant comes from water density, specific heat, and unit conversions in US customary calculations. It provides an accepted shortcut for estimating heat transfer in circulating water systems near standard operating conditions.
8. Does weather affect real cooling tower capacity?
Yes. Real tower capacity changes with wet bulb temperature, airflow, fouling, water distribution, and mechanical condition. Field performance may differ from simple calculations, especially during seasonal humidity swings or partial-load operation.