Cooling Towers: Balancing Efficiency, Water, and Sustainability

Different cooling technologies offer unique advantages, yet cooling towers play a key role in industrial and commercial applications, particularly where water availability and operational Priorities justify their use. This article shares insights gained by Federico Dogana on cooling tower operation, key maintenance challenges, and performance optimisation, breaking down how they work, their critical components, and why proper maintenance is essential for efficiency and longevity.

Through his work with adiabatic cooling technology, Federico frequently encountered evaporative cooling towers. While he spent years focusing on water-saving solutions, industry interactions and hands-on experience have given him a deeper understanding of cooling towers—their operation, benefits, and limitations.

Cooling Towers

Cooling towers are widely used to reject heat in industrial processes or HVAC systems, dissipating heat into the atmosphere. Typically, they work with chillers’ condensers or other heat exchangers to absorb heat from process equipment or air handling units (AHUs). For instance, in large buildings, HVAC chillers absorb indoor heat, which must be rejected. Cooling towers use evaporative cooling to achieve this efficiently.

(Image caption: Large-scale cooling towers. These systems are essential for heat rejection, contributing to efficient temperature control across various applications. (Image from Vecteezy)

How Cooling Towers Work: The Heat Rejection Cycle

The heat rejection cycle
The cooling process operates in a straightforward but highly effective cycle: Air is pulled through the tower. A fan at the top draws air upward, creating Warm water that enters the tower. Water carrying excess heat from the chiller or industrial process is pumped to the cooling tower.

• Warm water enters the tower – Water carrying excess heat from the chiller or industrial process is pumped to the cooling tower.
• Water is distributed over the fill. The warm water is sprayed through nozzles onto fill packaging, a structured medium that increases the surface area for heat transfer. As it moves downward by gravity, maximum heat exchange occurs
• Air is pulled through the tower. A fan at the top draws air upward, creating a counterflow effect where air moves opposite to the falling water, enhancing cooling efficiency.
• Evaporative cooling takes place. Some evaporate as air passes over the water, carrying heat away. This process is primarily driven by the latent heat of evaporation, where water absorbs heat and transitions into vapor, effectively removing energy from the system. A smaller portion of the cooling effect comes from sensible heat exchange, which lowers the water temperature without a phase change.
• Cooled water is collected and recycled – The now-cooled water collects in a basin at the bottom of the tower, where it is recirculated to absorb more heat from the system.

Why it works: Cooling towers efficiently utilise the latent heat of evaporation, making them an effective heat rejection solution. While alternative technologies like adiabatic and dry coolers offer benefits in specific applications, cooling towers remain widely used, particularly where water availability and operational priorities justify their use

(How an open cooling tower works: Heat is transferred from process water to the air through evaporative cooling, lowering the water temperature before it returns to the chiller or heat exchanger)

Components of a cooling tower
Cooling towers consist of several critical components that ensure efficient heat rejection:Fan—

• Fan Pulls air through the tower, increasing airflow and improving heat transfer.
• Fill Packaging (Fill Media)—Provides a large surface area for water to spread, enhancing evaporative cooling efficiency.
• Spray Nozzles—Evenly distribute warm water over the fill packing, ensuring maximum contact between water and air.
• Drift Eliminators (option)—Prevent water loss by capturing droplets before they escape with the exhaust air, reducing water waste.
• Basin – Collects cooled water before it is recirculated back into the system.
• Blowdown & Drain : This removes accumulated impurities and excess dissolved solids, preventing scaling and fouling. It also facilitates maintenance tasks such as cleaning, descaling, and inspections.
  s.
• Makeup Water System: This system automatically replenishes lost water due to evaporation, blowdown, and drift, maintaining system balance.

Each component must function correctly to maintain system efficiency, reduce energy consumption, and
slow scaling and fouling. Proper and consistent water treatment is essential to ensure long-term performance.

Evaporative cooling & water consumption

A key characteristic of cooling towers is evaporative cooling, which effectively removes heat but results in significant water consumption. This water loss occurs through three main mechanisms.

Evaporation loss (E) happens when water turns into vapour, absorbing heat, specifically the latent heat of
evaporation, thereby removing energy from the system. Drift loss (D) refers to small water droplets that escape with the exhaust air; Small water droplets escape with the exhaust air. Drift eliminators help minimize this loss, improving water efficiency and reducing the environmental impact of airborne and chemically treated chemicals. Blowdown water loss (B) occurs when a portion of the circulating
water is purged and replaced to control mineral buildup and maintain proper water chemistry, preventing scaling

To compensate for these losses, required Makeup Water (MU) must be added to the system, calculated as MU = E + B + D. Efficient water management in cooling towers is essential to reducing waste, lowering operating costs, and minimising environmental impact.

Importance of proper maintenance & water treatment

Cooling towers require proactive maintenance to prevent performance issues, improve efficiency, and extend the system’s lifespan. Key challenges include scaling, which is caused by the accumulation of mineral deposits (dissolved solids) on heat exchange surfaces and reduces heat transfer efficiency. Fouling, another common issue, involves the buildup of dispersed solids, dirt, and biological material that
Restrict water flow and further decrease system performance.

Microbial growth and the associated risk of Legionella are also significant concerns, as Biofilm buildup can act as an insulating layer, reducing heat transfer efficiency and increasing energy costs. Additionally, biofilm can create an ideal environment for Legionella bacteria, posing serious health risks if not managed through regular monitoring and treatment. Further, poor water quality management leads to excessive scaling, fouling, and microbial contamination, increasing maintenance and operational costs.

Best practices for maintenance

The best maintenance practices to address these challenges include regular water treatment to prevent scaling, corrosion, and bacterial growth by maintaining proper water chemistry. Periodic cleaning and descaling are essential to help remove deposits and ensure optimal heat transfer efficiency.

Using drift eliminators and conducting basin checks helps reduce water loss by capturing drift droplets and ensuring proper circulation to prevent stagnation and sediment buildup. Furthermore, periodic inspections of airflow and fan operation ensure the fan operates efficiently, maximizing heat rejection.

Why cooling towers matter for energy efficiency

Poorly maintained cooling towers waste energy and increase costs. Scaling, fouling, and biofilm deposits reduce heat transfer efficiency, forcing chillers to work harder, leading to higher electricity consumption and maintenance expenses.

Optimising cooling towers can lower energy consumption by improving heat transfer efficiency and reducing the chiller workload. It also helps reduce operating costs by minimising water waste and improving overall system efficiency. Additionally, it supports sustainable operations by reducing environmental impact through improved water and energy management. Companies investing
in high-efficiency cooling towers, variable speed fans, and advanced water treatment systems can see significant savings in long-term operations.

Conclusion: optimising cooling tower performance

Cooling towers continue to be a widely used industrial and commercial cooling solution. While they require careful water management and maintenance, their effectiveness makes them a reliable choice when properly designed and operated.

Understanding core principles and best practices is key to maximising performance, reducing costs, and
ensuring long-term reliability. Whether you are an engineer, facility manager, or industry professional, applying optimised cooling tower strategies can improve efficiency, cost savings, and sustainability.