Are cooling tower fans supposed to blow out

The correct direction of the fan is a crucial step in the operation and maintenance of the cooling tower. Many people have questions after repairing or replacing the motor: Should the cooling tower fan blow outward or suck inward? This article will provide a detailed explanation of this issue starting from the types of cooling towers, fan structures, and operating principles.

Overview of the working principle of cooling tower fan

The function of a cooling tower is to use the heat exchange between air and circulating water to cool down the hot water and recycle it for use. There are two main ways for air to enter the cooling tower:

1.Induced Draft: 

A fan is installed at the top of the tower to extract air from the tower, allowing it to enter from the side or bottom of the tower. This is the most common type.

2.Forced Draft: 

A fan is installed on the side of the tower to forcefully send air into the tower.

Common cooling tower fan direction: Should it be "blowing outward" or "blowing inward"?

1. The vast majority of cooling towers: fans should "blow outward"

For the most common counterflow and cross flow induced draft cooling towers (with packing inside the tower and fans at the top),

The function of the fan is to extract air from the tower, creating negative pressure and allowing air to enter from the side/bottom of the tower.

✔  Conclusion: The fan should blow outward (extract air).

Reason:

1. Reduce water mist dispersion (reduce water drift)

The exhaust method allows the airflow to rise evenly, making it easier for water droplets to be captured by the float.

2. Increase air flow rate for high cooling efficiency

A stable negative pressure is formed by exhaust, which draws in air and distributes it more evenly when passing through the fill.

3. Avoid reflux and short circuit

Exhaust air away from the tower to prevent hot and humid air from being sucked back into the tower.

4. The fan is less susceptible to water vapor corrosion

The fan is located at the exhaust end and does not directly come into contact with humid and hot air.

If it turns in the opposite direction and blows inward, it will cause:

1) The air volume drops sharply

2) The cooling effect has significantly deteriorated

3) A large amount of drifting water flies out

4) The current of the fan increases, and it may even vibrate or be damaged

2. Forced ventilation cooling tower: The fan blows inward

Although relatively rare, some large industrial cooling towers adopt a forced ventilation design with side inlet fans, which blow air into the tower and then discharge it from the top.

✔  Conclusion: The forced ventilation cooling tower fan blows inward (supply air).

But this is not a common tower type among the public.

How to determine if the wind direction of your cooling tower fan is correct?

You can quickly determine from the following methods:

Method 1: Observe the blade curvature and installation direction

The design of fan blades has a fixed direction, and if installed incorrectly or the motor is reversed, it can lead to incorrect wind direction.

Method 2: Check the airflow direction when starting the fan

Place your hand on the top outlet of the fan (safe distance) and feel:

Air up → fan blowing outward, correct

Air downward → the fan blows inward, then reverses direction

Method 3: Check the water mist

If the fan rotates in reverse, you will see:

1）A large amount of water mist is pressed back into the tower → abnormal

2）Water mist splashing from the side wall of the tower → abnormal

Method 4: Check the motor current

When reversing, the efficiency of the fan is extremely low, and the current is generally high.

Summary

80% -90% of cooling tower fans should blow outward (exhaust),extract air from the top of the tower and allow it to enter the tower from the side or bottom.

Only a few forced draft cooling tower fans blow inward.