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The cooling towers or water cooling towers are equipment that bases their operation on the principle of evaporative cooling, which has been applied in the industry for more than 100 years. Evaporative cooling is a natural process that uses water as a refrigerant and is applied to transmit to the atmosphere the excess heat of different thermal processes and machines.

Broadly speaking, evaporative cooling equipment, such as cooling towers, incorporates: a heat and mass exchange surface moistened by a water distribution device, a ventilation system (natural or forced) to favor and, in its case, forcing the passage of ambient air through the heat and mass exchange filler, and different auxiliary components such as a water collection basin, recirculation pump, droplet separators and control instruments. Next we will explain step by step the process of operating a cooling tower:

  • Operation of a cooling tower
  • Cooling towers with natural draft.
  • Cooling towers with induced draft.
  • Forced draft cooling towers.
  • Stream flow towers.
  • Benefits
  • Security and Legionella.

How does a cooling tower work?

The operation of a cooling tower is based on the principles of evaporative cooling:

The cooling towers cool the hot water by spraying it in the form of a rain of droplets that fall into a lattice or exchanger filling where they are cooled by means of a current of air, which flows in the opposite direction, dropping the already cooled water into a reservoir that collects and that, in your case will be distributed by a circuit.

The air enters through the lower openings that are above the water tank and through the tower from bottom to top. This air intake can occur naturally in the towers of natural draft or forced form through strategically placed fans, as we will explain later when we talk about the types of towers that exist.

Heat transfer occurs when water (at higher temperature) and air (at lower temperature) converge in the tower filling, where heat exchange takes place between the two fluids. This filling has the purpose of increasing the surface and the contact time between the air and the water, promoting the cooling efficiency. When evaporating, the water takes the heat it needs from the rest of the circulating water, cooling it.

In this process, approximately 1% of the total water flow evaporates for each 7ºC of cooling. This water that leaves the evaporated tower is filtered through the so-called “droplet separator”. This is one of the most important elements for the safety of a cooling tower, since it avoids the risk of water contaminated by the Legionella bacteria leaving freely to the outside. This element, which has losses lower than 0.002%, efficiently reduces the expulsion of water into the atmosphere as dictated by the UNE 100030/2017 standard. According to this norm and for security, the separators of drops must be replaced every 10 years.

The rest of the refrigerated water is deposited in a raft that sends it to a circuit that will use this refrigerated water in different applications (air conditioning, air treatment units, industrial processes, etc.)

Types of cooling towers

According to its design, we can find different types of cooling or cooling towers. The fundamental difference between one and the other lies in the way in which they enter the air in the tower to cool the water, which can be naturally or forced by fans.

Cooling towers with natural draft

The necessary air flow is obtained as a result of the difference in densities, between the cooler air outside and wet inside the tower. They use tall chimneys to get the desired shot. Due to the large dimensions of these towers, water flows of more than 200,000 gpm are used. They are widely used in thermal power plants.

Induced draft cooling tower

In this type of towers, the air is sucked by a fan located at the top of the tower. They are the most used because they are more efficient than other models.

Forced shot towers

The air is forced by a fan located at the bottom of the tower and discharged from the top. These types of towers are less efficient since the download speed is lower.

Cross flow towers

The air enters through the sides of the tower flowing horizontally through the falling water. These towers need more air and have a lower operating cost than countercurrent towers.

Benefits of using cooling towers

The use of cooling towers or other components that are based on the evaporative cooling of water has numerous benefits when compared to other types of cooling systems that are based on the use of refrigerants. Manuel Lamúa, Secretary General of ANEFRYC, explains them in an extended way in the article: Benefits of evaporative cooling. Some of these benefits are:

  • Greater energy saving
  • They require less investment than air condensers
  • They have a lower environmental impact
  • Less water consumption
  • Less acoustic impact

Safety of cooling towers: avoid Legionella

However, the truth is that evaporative cooling equipment is only susceptible to develop the bacterium “legionella pneumophila”, that is, increase the concentration thereof in the water that recirculates, if the water it receives from the network is contaminated and the equipment is not maintained properly, as required by law (Royal Decree 865/2003) that establishes 2 annual inspections and cleaning of the device, they are completely safe.

  • The standard operating conditions of a cooling tower can create a sufficient environment for the proliferation of legionella, but for the appearance of an outbreak several circumstances have to occur simultaneously:
  • Presence of a contaminated strain in the refrigeration system
  • Uncontrolled conditions
  • Drops of contaminated water expelled into the atmosphere
  • Inhalation of a sufficient quantity of microdroplets


Control y Ventilacion, S.L. is a company of international renown within the industrial and livestock sector, for being a manufacturer of products within the evaporative cooling sector, such as the HUMIBAT, evaporative plastic cooler; or its NUCLEOS towers, Cooling Towers. In both products, the substrate in which the evaporative process is produced is a plastic honeycomb, a honeycomb resistant both to physical and chemical attacks, and at the same time flexible, a honeycomb with a mesh structure, made of polyethylene High Density, and marketed under the names of PANAL C & V or in the case of being a drop separator, SEPARADOR C & V .

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