Cooling Tower Performance: Key Calculations, Efficiency, and Fan Curves
Optimizing cooling tower performance isn’t just about airflow—it’s about understanding the nuances of thermal transfer, water balance, and fan dynamics.
1. Cooling Tower Effectiveness:
This is a measure of how effectively the cooling tower brings the water temperature close to the ambient wet-bulb temperature.
Effectiveness is calculated as:
Effectiveness (%) = (Range / (Range + Approach)) × 100
2. Cycle of Concentration (COC) vs Makeup Water:-
COC represents how many times water is cycled through the system before being discharged as blow down. The higher the COC, the less makeup water is required, thus conserving water.
Makeup Water Calculation:- Makeup Water = Evaporation Loss + Blow down + Drift Loss Increasing COC can reduce makeup water demand but also requires careful management of water quality.
3. Blowdown vs COC:-
Blowdown removes dissolved solids and controls scaling in the system. As COC increases, the blowdown rate reduces: Blowdown = Evaporation Loss / (COC – 1)
4. ID Fan Performance Curves:-
The ID (Induced Draft) Fan is crucial in driving airflow through the cooling tower. The performance curve helps engineers design for optimal fan operation by plotting Static Pressure vs Airflow. The optimal fan curve is where system resistance equals fan capacity, ensuring the tower operates at peak efficiency with minimal energy consumption.
5. Average Cooling Tower Efficiency: –
Typical efficiency falls between 60-75%, depending on design and operational parameters. Highly efficient towers can reach up to 85-90%, especially with well-maintained ID fans, optimized COC, and proper chemical treatment.