Calculator Inputs
Example Data Table
Use this example to validate your setup and expected output pattern.
| Example Case | Chiller Load (TR) | Factor | Hot (°C) | Cold (°C) | Wet-bulb (°C) | Heat Rejection (kW) | Flow (m³/h) | Recommended (tons) |
|---|---|---|---|---|---|---|---|---|
| Office Building | 250 | 1.25 | 35 | 29 | 25 | 1,099.1 | 157.7 | 312.5 |
| Process Cooling | 400 | 1.20 | 40 | 32 | 26 | 1,688.2 | 181.5 | 528.0 |
Formula Used
- Range (°C) = Hot Water (°C) − Cold Water (°C)
- Approach (°C) = Cold Water (°C) − Wet-bulb (°C)
- Heat Rejection (kW) = Chiller Load (TR) × 3.517 × Factor (when using TR method)
- Mass Flow (kg/s) = Heat Rejection (kW) ÷ [Cp (kJ/kg·K) × Range (°C)]
- Circulation Flow (m³/h) = Mass Flow (kg/s) ÷ Density (kg/m³) × 3600
- Tower Capacity (tons) = Heat Rejection (kW) ÷ 3.517
- Evaporation Loss (m³/h) ≈ 0.0018 × Flow (m³/h) × Range (°C)
- Drift Loss (m³/h) = Flow (m³/h) × Drift% ÷ 100
- Blowdown (m³/h) = Evaporation ÷ (COC − 1)
- Make-up (m³/h) = Evaporation + Drift + Blowdown
How to Use This Calculator
- Pick an input method: start from chiller load or known heat rejection.
- Enter hot water, cold water, and local wet-bulb temperatures.
- Set cycles of concentration and drift percent to estimate make-up water.
- Adjust the safety margin to match your design philosophy.
- Open Advanced Inputs if you want to tune Cp, density, or airflow estimates.
- Click Calculate to view results above the form, then export CSV or PDF.
Engineering Notes
Load definition and sizing intent
Cooling tower sizing starts with heat rejection, not fan power. The key inputs are circulating flow, hot and cold water temperatures, and the design wet‑bulb. From these, the calculator estimates total heat rejection and a nominal tower capacity, helping you compare options during early planning and budget cycles. Use it to screen alternates before detailed vendor selection.
Range, approach, and wet‑bulb margin
Range is the hot‑to‑cold temperature drop, while approach is the cold‑water temperature minus wet‑bulb. Smaller approach requires larger fill area and higher airflow. Many projects select a 4–7 °F approach for a balanced footprint, then confirm performance with vendor curves at the site wet‑bulb percentile and seasonal extremes.
Heat rejection and evaporation allowance
Heat rejection is calculated from water flow and temperature change, then translated to tonnage. A practical check is evaporation: typical evaporative loss is a small percentage of circulation, increasing with range. Drift and blowdown add to makeup needs, so the calculator reports approximate evaporation and total makeup for utility sizing.
Airflow, fan selection, and elevation effects
Airflow demand rises as approach tightens or wet‑bulb increases. At higher elevations or in hot climates, reduced air density can lower capacity, so designers often include a margin or specify variable‑speed drives. The calculator provides a baseline airflow estimate to support duct, plenum, and electrical planning.
Example data for concept validation
Example: Flow 1,200 gpm, hot 95 °F, cold 85 °F, wet‑bulb 78 °F yields a 10 °F range and 7 °F approach. The estimated rejection is about 6,000,000 Btu/h (≈500 tons). With 1.0% evaporation, makeup is roughly 12 gpm plus drift and blowdown allowances. This is concept data; confirm final duty with certified performance ratings.
FAQs
What is the difference between range and approach?
Range is the hot‑to‑cold water temperature drop. Approach is the cold‑water temperature minus the design wet‑bulb. Range drives heat load; approach drives tower size because smaller approach requires more fill and airflow.
Why does wet‑bulb temperature matter so much?
Evaporative towers cool toward the ambient wet‑bulb, not the dry‑bulb. Higher wet‑bulb reduces the achievable leaving‑water temperature, so capacity drops unless tower size or airflow increases.
How accurate is the tonnage estimate?
It is a planning estimate based on heat balance and typical conversion factors. Use it for concept sizing, comparisons, and utility checks. Final selection should use manufacturer performance curves and certified ratings for the exact site conditions.
How do I estimate makeup water?
Makeup is driven by evaporation, drift, and blowdown. The calculator estimates evaporation from heat rejection and lets you include drift and cycles of concentration to approximate blowdown, producing a practical total makeup flow for piping and water treatment planning.
Should I include a safety margin?
Yes. Many designers add margin for fouling, seasonal extremes, and off‑design operation. A common early allowance is 5–15%, then refine during vendor selection, water quality review, and commissioning requirements.
What inputs most affect airflow and fan power?
Approach and wet‑bulb are the biggest drivers. Tighter approach or higher wet‑bulb requires more airflow, increasing fan demand. Elevation, recirculation, and inlet restrictions can also increase required airflow and reduce net capacity.
Can one tower serve multiple loops or heat sources?
Often yes, if flows are combined and control valves maintain required temperatures. Use the calculator to total heat rejection and expected leaving temperature, then verify hydraulics, turndown, and redundancy with a detailed mechanical design.