What Is a Cooling Tower?
A cooling tower is a heat removal device that extracts excess heat from industrial processes, HVAC systems, or power plants and releases it into the atmosphere, typically by cooling a stream of water. The hot water enters the cooling tower, where it is cooled through air contact and evaporation before being recirculated back into the system. This helps maintain optimal temperatures in various systems and allows for efficient operations. In this post, we’ll explore how water is transported, cooled, consumed, and reused in cooling towers, as well as environmental impacts and strategies for improving efficiency.
How Does Water Move Through a Cooling Tower?
Water movement in a cooling tower follows a continuous loop. Here’s a step-by-step breakdown:
Water Intake: Hot water from the system that needs to be cooled enters the cooling tower through a system of pipes or conduits.
Water Distribution: The hot water is distributed over the cooling tower fill, a porous medium that increases the water's surface area, allowing for maximum exposure to the airflow within the tower.
Cooling Process: The distributed water comes into direct contact with air in the tower. The air, typically forced through the system using fans, causes some of the water to evaporate, cooling the remaining water.
Cold Water Collection: The now cooled water collects in a basin at the bottom of the cooling tower, from where it is pumped back into the system to absorb more heat.
What Happens to the Water During the Cooling Process?
As the hot water flows over the cooling tower fill and air is blown through it, part of the water evaporates. This evaporation removes heat from the remaining water, which cools it down. The rate of evaporation is influenced by several factors, such as heat load, temperature, humidity, and the type of cooling tower being used. On average, cooling towers continuously lose about 1-3% of their circulating water to evaporation, depending on operating conditions and the efficiency of the system.
In addition to evaporation, water is lost through wastewater blowdown and drift. All of the lost water has to be replaced with new freshwater. This is done through a makeup water supply, which replenishes the water lost during the cooling process from a freshwater source.
The Role of Evaporation in Cooling Towers
Evaporation plays a critical role in cooling tower operations, as it is the primary mechanism for removing heat from the water. When hot water from the system is distributed over the cooling tower fill, a portion of the water evaporates as it comes into contact with air, carrying away the excess heat. This evaporation, combined with plumes formed from water vapor discharge, results in a substantial loss of water. Both must be replenished through makeup water, increasing overall water consumption.
As water vapor is discharged as waste, it condenses into microscopic droplets of water and forms the characteristic plume of fog that can typically be seen in cooling towers. Those droplets contain high-purity water.
One approach to reduce water consumption is to capture those droplets and re-use their water content. This can be achieved with Infinite Cooling’s plume capture technology, WaterPanel.
What Is Blowdown and Why Is It Necessary?
Cooling towers continuously recirculate water, but as water evaporates, it leaves behind dissolved solids such as minerals, salts, and other impurities. Over time, these impurities can concentrate and lead to scale formation, corrosion, or biofouling in the system.
To manage this, cooling towers regularly discharge a portion of the circulating water in a process called blowdown and they replace it with new freshwater. This helps to remove concentrated impurities and maintain water quality. Blowdown-related water consumption is usually 5-30% of the losses due to evaporation. Discharged water typically needs to be treated before discharge into waterways and the process is often regulated with NPDES permits.
What Is Drift in a Cooling Tower?
Another form of water loss from cooling towers is drift, which consists of small droplets of water that are carried out with the tower’s exhaust air without evaporating. These droplets contain dissolved solids, chemicals, and bacteria, so it’s important to minimize drift to reduce water consumption and prevent environmental contamination. Numerous hazards can be caused by drift including the spread of Legionella bacteria responsible for deadly Legionnaire’s disease, corrosion of nearby equipment, and scale buildup.
Cooling towers are equipped with drift eliminators, devices designed to passively capture and return a majority of these water droplets to the system before they escape into the atmosphere, but a fraction of the droplets still escape. Efficient drift control is important for both water conservation and reducing the environmental impact of cooling tower operations.
Makeup Water and the Importance of Water Quality
Makeup water refers to the fresh water added to the cooling tower system to compensate for losses due to evaporation, plumes, blowdown, and drift. The amount of makeup water needed depends on the tower's size, the temperature of the incoming water, and the system's conditions.
Water quality plays a significant role in determining the performance and longevity of a cooling tower. Poor-quality water can lead to all kinds of maladies:
Scaling: The buildup of minerals like calcium and magnesium that can reduce heat transfer efficiency.
Corrosion: Deterioration of metal components due to dissolved salts or gasses in the water, leading to system failure or costly repairs.
Biofouling: The accumulation of organic material, such as algae or bacteria, which can clog the cooling system and reduce efficiency.
To prevent these issues, proper water treatment is essential. This typically includes chemical treatments, such as anti-scalants and biocides, as well as filtration systems to maintain water quality within acceptable limits. The type and level of treatment depends on the makeup water quality and operational profile.
What Are the Environmental Impacts of Water Use in Cooling Towers?
Cooling towers significantly impact water resources, raising environmental concerns primarily due to two key issues:
Water Consumption: Cooling towers account for over 50% of all industrial and commercial water use in the U.S. his heavy reliance on water is particularly concerning in arid regions, where balancing usage with local availability is crucial for sustainable operations.
Water Discharge: The blowdown and drift from cooling towers can carry contaminants such as biocides, corrosion inhibitors, and scaling agents, as well as concentrated heavy metals and salts into nearby water bodies. If not properly treated, these discharges can harm aquatic ecosystems.
To mitigate these environmental impacts, operators often implement water conservation strategies, such as utilizing recycled water for makeup and minimizing blowdown with more treatment. Infinite Cooling’s TowerPulse™ technology enhances this effort by continuously monitoring and optimizing cooling tower performance, while WaterPanel™ technology captures and recycles water lost in plumes, significantly reducing water consumption and improving the sustainability of cooling tower operations.
How Infinite Cooling is Making Water Use More Efficient
Infinite Cooling is revolutionizing water use in cooling towers with its integrated technologies, TowerPulse™ and WaterPanel™, which work together to maximize efficiency. TowerPulse™ is a real-time monitoring system that tracks key parameters like water consumption, cooling efficiency, and equipment performance, providing precise data that enables operators to fine-tune water usage and minimize waste. WaterPanel™ complements this by capturing water lost in evaporation plumes and recycling it back into the system. By working in tandem, TowerPulse™ optimizes cooling tower performance, while WaterPanel™ ensures minimal water loss. Together, these technologies reduce both water and energy consumption, making cooling towers more sustainable and cost-efficient, particularly in water-scarce regions.
Conclusion
Water is essential to the operation of cooling towers, serving as the medium through which heat is absorbed and released. Understanding how cooling towers use water can help improve efficiency, reduce water consumption, and mitigate environmental impacts. By combining TowerPulse™ and WaterPanel™, cooling towers can operate more efficiently and sustainably. Learn more about how Infinite Cooling can help your facility save water and reduce costs.