How to calculate cooling tower fan power

Cooling tower is a common heat exchange equipment in industrial and HVAC systems, and the fan, as one of the core components of the cooling tower, directly affects the cooling effect and energy consumption in terms of its power. Accurately calculating the power of cooling tower fans not only helps with rational selection, but also improves system operating efficiency and reduces energy consumption. This article will introduce the basic calculation method, relevant parameters, and key points to be noted in the design of cooling tower fan power.

Basic principles of wind turbine power calculation

The power of a fan essentially comes from the work done by the fan on the air. After passing through the fan, the pressure and flow rate of the air increase, and the shaft power (also known as input power) of the fan depends on the air volume, air pressure, and fan efficiency.

The basic calculation formula is：P=Q×H/η×102

among which

P - Fan power (kW)

Q - Airflow (m ⊃3;/s)

H - Full pressure of fan (Pa or N/m ⊃2;)

η - Efficiency (including fan efficiency, transmission efficiency, and motor efficiency)

102- Unit Conversion Factor

Key parameter description

1. Airflow (Q)

The air volume represents the volume of air delivered by the fan per unit time and is an important design parameter for cooling towers.

For cooling towers, the air volume mainly depends on:

1）Fill resistance

2）Tower structure

3）Cooling water volume (L/G ratio)

4）Expected cooling effect

The air volume is generally provided by the manufacturer or estimated based on empirical formulas.

2. Fan full pressure (H)

Fan full pressure is the pressure required for the fan to overcome system resistance.

The system resistance includes:

1）Fill resistance

2）Import and export wind resistance

3）Resistance of blinds

4）Pipeline or duct resistance (if any)

The full pressure range of the cooling tower fan is usually 60-200 Pa.

3. Efficiency (η)

The ratio of the actual power consumed by the fan to the theoretical power.

Efficiency generally includes:

1）Fan efficiency (0.6-0.8)

2）Motor efficiency (0.85-0.95)

3）Transmission efficiency (belt transmission is about 0.9, direct connection can reach 1.0)

The overall efficiency is generally estimated at 0.6-0.75.

Factors affecting fan power

1.Environmental impact

Air density varies with temperature and humidity; When the density decreases, the power demand decreases.

2.Fill blockage or aging

Resistance increases → wind pressure increases → power increases.

3.Changes in fan speed

The power and speed have a cubic relationship (similarity law).

4.Tower structure design

Unreasonable air outlet design can significantly increase resistance.