Why cooling tower fans have vfd

In modern cooling water systems, more and more cooling tower fans are configured with Variable Frequency Drive (VFD). Compared to traditional power frequency (fixed speed) operation, VFD can significantly improve the efficiency, stability, and operational economy of cooling towers. So, why do cooling tower fans need to be equipped with VFD? This article will comprehensively analyze from the perspectives of technical principles and engineering applications.

Why do cooling tower fans need frequency converters?

1. Control the cooling tower water temperature more accurately

The main goal of a cooling tower is to maintain the water temperature within a set range. Traditional fans have a fixed speed and can only operate through:

1）Turn on/off the fan

2）Start different numbers of fans

Roughly adjust the water temperature.

But this will lead to:

1）Large fluctuations in water temperature

2）Frequent start stop of fan

3）High starting current

And the frequency converter can automatically adjust the fan speed according to the return water temperature, achieving precise temperature control:

1） Slightly higher temperature → Acceleration fan

2） Normal temperature → Decrease speed

3） Low temperature → maintained at low speed, not too cold

In this way, the water temperature control is smoother and the response is softer.

2. Significant energy-saving effect (energy consumption can be reduced by 20% -60%)

The cooling tower fan belongs to high air volume equipment, and the theoretical relationship of air volume is:

Air volume ∝ speed

But more importantly:

Fan power ∝ speed ⊃3;

This means:

1）The speed decreases by 20%, and the power decreases by nearly 50%

2）The speed decreases by 30%, and the power decreases by nearly 65%

Therefore, slightly reducing the speed can save a lot of electricity.

In most seasons, it is not necessary for the fan to run at full speed. Using VFD can make the fan work according to "actual needs", and the energy-saving effect is very prominent.

3. Reduce fan noise

The maximum noise is generated when the fan is at its fastest speed. After using the frequency converter:

1）Most of the time, the fan runs at a lower speed

2）Significant reduction in noise (3-10 dB)

The effect is particularly evident for noise sensitive places such as office buildings, hospitals, and residential areas.

4. Avoid overcooling and increased water mist in winter

In the low temperature season, fixed speed fans are prone to lowering the water temperature too low, affecting the process or equipment, while low-speed operation is more stable and safe.

In addition, high-speed operation of the fan will bring a large amount of floating water, and reducing the speed appropriately can significantly reduce the escape of water mist.

Which cooling towers are most suitable for using VFD?

1.Medium to large counter current/cross flow cooling tower

2.Tower driven by gearbox

3.HVAC systems with significant load changes

4.Industrial cooling systems (chemical, power generation, manufacturing)

5.Scenarios requiring variable cross-sectional air volume control

Especially suitable for regions and processes with unstable temperatures and frequent changes in cooling loads throughout the year.

Potential issues with using VFD (to be aware of)

Although VFD has many benefits, it also requires proper configuration:

1）High frequency pulses may increase the insulation pressure of the motor (requiring a dedicated variable frequency motor or adding a dv/dt filter)

2）If the temperature sensor malfunctions, it may cause the fan to adjust its speed incorrectly

3）The installation environment of the frequency converter needs to be dry and ventilated

Choosing appropriate specifications and protective measures can avoid most problems.