What Is a Cooling Tower? How They Work, Maintenance & More

Cooling towers are found in large commercial buildings to help regulate heat within heating, ventilation, and air conditioning (HVAC) systems, specifically water-cooled air conditioners. They work by extracting excess heat from the water, improving the overall efficiency of the system. In this article, I dove into why a cooling tower is necessary in some HVAC units, the different types, and how they can be properly maintained to extend their lifetime and performance.

Cooling Tower Basics

Cooling towers are usually designed to work with HVAC units as part of the cooling system. They process water to dissipate the heat in the recirculating water system that comes from the chiller. Cooling towers are often found on the rooftops of large commercial buildings, hospitals, and other facilities that require extensive cooling. Once the water is cooled, the cold water is returned to the chiller, where it heats up again and the cycle is repeated.

They can also be found separate from HVAC systems in power plants, manufacturing facilities, and chemical plants where excess heat management is a must.

Cooling towers are a necessity to maintain the proper water temperature within the HVAC system or industrial process.

Different Types of Cooling Towers

There are three main types of cooling towers found with HVAC systems, including:

• Open cooling towers: Open cooling towers, also known as wet cooling towers, use the direct contact of water and air to transfer heat. In counterflow cooling towers, air will flow vertically upwards while the water flows downwards. In crossflow cooling towers, air will flow horizontally across the downward flow of water. 
• Closed cooling towers: Closed cooling towers, or dry cooling towers, don’t expose the water to the air. They instead use a heat exchanger to transfer heat from the water to the air.
• Hybrid cooling towers: Some HVAC systems use a mix of both open and closed cooling towers for improved efficiency and water usage.

How Does a Cooling Tower Work?

In HVAC systems, cooling towers are made up of five different components that cool the warm water. They include:

• Fill media: This is the material inside the tower that increases the surface area for water and air contact, which allows the cooling tower to improve the heat transfer process. It can also be called a “heat transfer medium.”
• Fans: Using either mechanical drafts or natural drafts, fans promote airflow within the tower. Induced draft cooling towers will have fans at the top of the tower. Forced-draft towers push air by using blowers at the base of the cooling tower.
• Water distribution system: This component sprays water over the fill media.
• Drift eliminators: These capture water droplets carried by the air to reduce water loss and prevent pollution.
• Basin: This collects the cooled water at the bottom of the tower before it is sent back to the chiller.

These components work together to cool the temperature of the water and then send the cold water back to the chiller, where it can collect heat again. Cooling towers’ operation falls into six steps:

1. Heat is absorbed. Hot water is sent to the top of the tower from the chiller (or industrial process).
2. Water is distributed. Using spray nozzles, the water distribution system sprays water over the fill media.
3. Air is moved. Using the fans or natural convection, air is drawn and pushed through the tower.
4. Heat is exchanged. Heat is transferred either through direct contact of water and air in open cooling towers, or it’s transferred through a heat exchanger in closed cooling towers.
5. Water evaporates. During these processes, water evaporates, further removing heat.
6. Water is collected. Once the water is cooled, it collects at the cold water basin located at the base of the tower. It’s then pumped back to the chiller or industrial process.

Once the water collects heat again, the cycle is repeated.

How To Maintain a Cooling Tower

Cooling towers, since they’re located on rooftops, can often be “out of sight, out of mind” for maintenance teams. However, they need regular care to improve efficiency, performance, and lifespan, while also lowering operating costs. Organizations should put cooling towers on their preventative maintenance schedules to make sure they’re properly cared for. 

Maintenance teams should:

• Perform water treatment. Water treatment is necessary to prevent bacteria growth and corrosion, while also keeping mineral deposits from building up.
• Clean spray nozzles. Algae, sediment, and solids can collect in the spray nozzles found with the water distribution system. Left unchecked, it can cause uneven water distribution and lower the tower’s efficiency.
• Clear debris. Clearing debris and dirt regularly can improve airflow. Poor airflow can result in fan and motor failures.
• Follow manual instructions. Every cooling tower comes with its own manual to improve maintenance and care. Follow your cooling tower’s instructions to create a maintenance schedule.

Water cooling towers are a necessary component of HVAC systems in large buildings. They keep the water cooled so the rest of the system can work properly. Their maintenance is sometimes ignored as they’re out of sight on the rooftop, but businesses and organizations need to implement maintenance schedules. This will help to make sure the cooling tower and the entire HVAC system are working as they should.