Cooling Towers

Cooling Towers

What is a cooling tower?

A cooling tower is heat removal device that uses water to transfer process waste heat into the atmosphere. All cooling towers operate on the principle of removing heat from water be evaporating a small portion of water that is recirculated through the unit.  The mixing of warm water and cooler air releases latent heat of vaporization, causing a cooling effect to the water.  They are a key component of many refrigeration systems and can be found in industries such as power plants, chemical processing, steel mills, and many manufacturing companies where process cooling is necessary.  Also, cooling towers can be used to provide comfort cooling for large commercial buildings like airports, schools, hospitals, or hotels.

Cooling towers might be one of the most vital part of any industrial process. These tall, open-topped, cylindrical structures are responsible for cooling water generated

from industrial or HVAC comfort cooling process. They are classified by the type of draft (natural or mechanical) and by the direction of air flow (counter or cross).

Natural Draft Cooling Towers are usually used for large power plants and industries with infinite cooling water flow. The tower operates by hot air in the tower rising removing waste heat and then releasing it into the atmosphere. These towers are tall and have a hyperbolic shape to induce proper air flow.

Mechanical Draft Cooling Towers have air forced through the structure by a fan that circulates air through the tower. Common fans used in these towers include propeller fans and centrifugal fans. While Mechanical draft towers are more effective than natural draft towers, they consume more power and cost more to operate as a result.

Crossflow Towers has a design that allows the air to flow horizontally through the fill and the tower’s structure into an open plenum area. Hot water flows downward from distribution basins. There is less recirculation because the speed of exit air is higher than entering air. However, fans and motor drive require weather-proofing against moisture which can lead to freezing making it less efficient.

Counterflow Towers has a design where the air is vertically upwards and the counter current with hot water is falling downwards to cool the air. This allows for maximum performance out of each plan area and helps minimize pump head requirements. Also, they are less likely to ice up in cold weather conditions and can save energy in the long run.

Induced Draft towers are typically mounted with a fan at the top of the cooling tower, which allows hot air out and pulls air throughout. The high exiting air velocities reduces the chance of re-circulation. To avoid the entrapment of water droplets in the leaving stream air, drift eliminators are used. Induced draft towers are more efficient as they use 30% to up to 75% less energy compared to forced draft designs.

Forced Draft towers are similar to induced draft but the basic difference is that the exhaust fan is placed at the base of the cooling tower, which allows the air to blow from the bottom. Their use is limited due to water distribution challenges, high horsepower fans and the possibility of re-circulation.

Here are the basics – five steps to maintain industrial cooling towers and chillers:

 1. Remove Scale Deposits

Since your cooling tower works by evaporation, you will experience periodic buildups of scale deposits on your fill. Minerals in the water can create these deposits, especially if you’re experiencing water treatment issues. Limescale buildup can decrease the efficiency and performance of your HVAC system and can lead to premature deterioration of your unit. Descale your system a few times per year to increase energy conservation and keep your monthly bills manageable.

2. Ensure Proper Airflow

Poor airflow is a common cause of air that doesn’t feel cold, poor fan performance, and even entire system breakdowns. Airflow interruptions can occur because of loose components, improper fan alignment, and lack of gearbox maintenance. Damage to your fan blades can also reduce airflow. Check your unit for debris within the tower or your fill. Your cooling tower may have sludge buildup on its basin floor that is blocking airflow. Use a tower vacuum to remove these contaminants. Adding a biocide can reduce the occurrence of bacterial and algae growth in your cooling tower.

3. Clean Your Tubes

Again, contaminants like mud, slime, algae, and scale can build up within your chiller tubes and cause a partial or total clog. Clogged tubes can lead to unit inefficiencies and breakdowns. How often you clean your tubes will depend on your water quality and rate of buildup. Every unit will experience buildup of some kind – it is the nature of the system. Clearing your chiller tubes of deposits regularly will prevent total blockages and make debris removal easier. You have miles of tubing in your industrial HVAC system – you may need help from a professional to completely clear your tubes and improve efficiency.

4. Inspect the Water Pump

Most chiller systems rely on a water pump to carry warmer water to the chiller for cooling. Efficiency during the pumping process can greatly increase the performance of your air conditioning, as well as save on monthly energy bills. A well-maintained pump will not have to work as hard to move water back and forth, making operation easier on your unit and increasing its life span. Inspect your pump and check to see if it is on and off when it should be. Your pumps should run when your chiller does. Lubricate your pump and motor bearingsso, as well as the water seal. Also, periodically check your alignment.

5. Treat Your Water

Cooling tower and chiller maintenance is about more than just making sure your HVAC system components are in adequate shape – you also must pay attention to you water quality. Water quality problems can lead to major scum and scale buildup, contributing to the breakdown of your system. Invest in effective water treatment to keep your system safe and at peak performance levels.