How to calculate cooling tower fan efficiency

The cooling tower is an important component of the industrial circulating water system, and as a key equipment of the cooling tower, the operating efficiency of the fan directly affects the energy consumption and cooling effect of the entire system. Therefore, correctly calculating the efficiency of cooling tower fans is of great significance for equipment selection, operation and maintenance optimization, and energy-saving evaluation.

The concept of cooling tower fan efficiency

Fan Efficiency measures the ability of a wind turbine to convert input mechanical energy into air energy (i.e. wind energy).

Fan efficiency is usually divided into three categories:

1.Static Efficiency:

Efficiency based on static pressure increments

2. Total Efficiency: 

Efficiency based on total pressure increments

3. Mechanical Efficiency: 

The efficiency of the motor output to the fan impeller

Formula for calculating fan efficiency

1.Total pressure efficiency (most commonly used)：ηtotal=Q×Pt/Pinput

Q: Airflow (m ⊃3;/s)

Pt: Fan full pressure (Pa)

Pinput: Input the power of the fan (W), usually the actual power of the motor (rather than the rated power)

2. Static pressure efficiency：ηstatic=Q×Ps/Pinput

Where Ps is static pressure

Measurement steps for cooling tower fan efficiency (practical version)

1. Record the nameplate data of the fan (power, speed, diameter, etc.)

2. Measure the actual input power of the motor

Using power meters

Or calculated based on U, I, PF

3. Measure wind speed

Using an anemometer

Distributed measurement point method (usually 9 points or more)

Calculate the average wind speed

4. Calculate the air volume Q

5. Measure or estimate the total pressure Pt

Measured using a micropressure gauge

Or use design values (for evaluation)

6. Substitute the efficiency formula to calculate efficiency

7. Comparison with the performance curve of the fan

Determine whether the fan is operating in the high-efficiency zone