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What Cooling Towers are used for?

You might have seen cooling towers located on the roof of tall buildings, or perhaps beside factories and power stations and wondered what they do. Put simply, a cooling tower transfers heat from water to the atmosphere.

Many processes use heat, while others, such as refrigeration and air conditioning, involve the transfer of heat from one place to another, what they have in common is a requirement to effectively deal with excess heat energy. The usual method to dispose of excessive heat energy is to reject it into the atmosphere, this can be done using a "dry cooler" such as a cars radiator which uses a fin heat exchanger to transfer heat from the hot fluid contained within to the air outside via aluminium or copper fins, or an "evaporative cooler" such as an open loop cooling tower which uses both direct heat transfer from the water to air as well as evaporation to remove the heat.

While there are many variations to the theme, a basic cooling tower will generally follow the same operation, the warm water is introduced to the top of the tower and runs over multiple layers of fill before reaching the basin at the bottom of the tower, the tower fill increases the surface area which the water flows over leading to greater heat exchange effectiveness, there is also a fan on the tower which is used to increase the air flow through the tower and over the water to improve the heat exchange. The evaporation of water means that there is a requirement for a water supply to the tower to replace the evaporated water.

The temperature of the water leaving the tower is controlled by increasing or decreasing the airflow through the tower, this can be done by a simple thermostatic control starting and stopping the fan, or a much more efficient method utilises a variable frequency drive (VFD) to control the speed of the fan motor so the airflow (and fan energy) is the minimum required to remove heat.

Cooling towers can have a significant impact on the efficient operation of the process which the cooling system is part of. For example, if a cooling tower which is part of a commercial building air-conditioning system has the water temperature set point too low then the system will use excessive energy to run the cooling tower fans. Conversely, if the water temperature set point is too high then the chiller compressors will need work harder and will use excessive energy, like most things in life, it is important to get the balance just right!

Cooling towers require regular maintenance to ensure that they are operating efficiently and also to prevent bacterial contamination. This should include regular cleaning and effective chemical treatment and water testing. An open loop cooling tower which is operating and maintained correctly will help to reduce the energy used by the entire process as well as minimising water and chemicals used by the tower.

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