Cooling Tower Approach Inputs
Example Data Table
| Scenario | Hot (°C) | Cold (°C) | Wet Bulb (°C) | Approach (°C) | Range (°C) | Effectiveness (%) |
|---|---|---|---|---|---|---|
| Peak afternoon | 36.0 | 29.0 | 26.0 | 3.0 | 7.0 | 70.00 |
| Moderate load | 34.0 | 28.5 | 25.5 | 3.0 | 5.5 | 68.75 |
| Night operation | 32.0 | 27.0 | 24.0 | 3.0 | 5.0 | 62.50 |
Formula Used
- Approach:
Approach = Tcold − Twetbulb - Range:
Range = Thot − Tcold - Effectiveness:
Effectiveness = Range / (Range + Approach) × 100
Thot − Twetbulb, representing the maximum theoretical cooling potential.
How to Use This Calculator
- Record hot and cold water temperatures at stable load.
- Capture local wet bulb near the tower intake air.
- Select the correct unit and enter temperatures.
- Optionally add a target approach for quick comparison.
- Press Calculate to view results above the form.
- Use CSV or PDF export for commissioning documentation.
Practical Notes on Cooling Tower Approach
Cooling tower approach is the temperature difference between the leaving cold-water temperature and the ambient wet-bulb temperature. It is one of the most useful indicators of tower health because it links thermal performance to real atmospheric cooling potential. In commissioning and troubleshooting, approach helps you separate a true capacity limitation from normal changes in weather and load.
A smaller approach generally indicates better heat rejection, but it is not “free.” Very low approach targets can require higher fan power, larger fill volume, tighter water distribution, and careful drift and plume control. Conversely, a rising approach at similar wet-bulb conditions often points to reduced airflow, scaled or fouled fill, clogged nozzles, or recirculation of warm discharge air back into the intake.
Use stable, representative readings. Measure wet bulb close to the tower intake and shield the sensor from direct sun and heat sources. Record hot and cold water temperatures after the system has reached steady operation (typically several minutes after large valve or speed changes). When comparing days, try to keep flow rate and heat load similar, because approach can increase if the tower is overloaded even when the wet bulb is unchanged.
When you report results, document the full context: wet bulb, hot-water temperature, cold-water temperature, estimated flow rate, fan status, and any bypass or three-way valve position. This makes trend plots meaningful and prevents false conclusions. If you have a specified acceptance test, align the measurement method with the specification (sensor locations, stabilization time, and correction factors, if any). For day-to-day operations, pairing approach with simple inspections and water treatment logs often catches problems early, before capacity shortfalls force chiller unloading or process temperature excursions.
Example: If hot water is 36 °C, cold water is 29 °C, and wet bulb is 26 °C, the approach is 3 °C and the range is 7 °C. If your design approach is 3 °C, the tower is performing close to intent. If the same load later shows cold water of 31 °C at the same wet bulb, approach becomes 5 °C, suggesting a performance loss that warrants inspection.
- Air side: verify fan rotation, speed control, belts, and unobstructed louvers.
- Water side: check basin level, distribution nozzles, and fill cleanliness.
- System: confirm flow rate and condenser cleanliness to avoid misleading temperatures.
- Data quality: calibrate sensors and log readings at consistent locations.
FAQs
1) What does “approach” tell me that range does not?
Range shows how much the tower cooled the water. Approach shows how close the tower gets to the wet-bulb limit, so it is better for comparing performance across changing weather.
2) Is a lower approach always better?
Not always. Lower approach usually improves cooling, but it may require more fan power or a larger tower. Targets should match design intent, energy goals, and site constraints.
3) Why does approach increase during peak load?
At higher heat load or water flow, the tower can reach its capacity limit. Cold-water temperature rises faster than wet bulb, increasing approach even when equipment is operating normally.
4) Where should wet-bulb temperature be measured?
Measure near the tower air intake, away from hot surfaces and direct sunlight. Poor placement or sensor bias can make approach appear worse or better than reality.
5) What operational issues commonly raise approach?
Reduced airflow, fouled fill, clogged spray nozzles, recirculation, and drift eliminator blockage are frequent causes. Water chemistry problems can accelerate scaling and biofouling.
6) Can I use approach to set fan control?
Yes. Many control strategies modulate fan speed to maintain a cold-water setpoint or a target approach. Use safeguards to avoid hunting and ensure stable sensor readings.
7) What is a reasonable acceptance check during commissioning?
Compare measured approach to the design approach at similar wet-bulb and load. If deviation is persistent, confirm instruments and flow first, then inspect tower airflow and distribution.