How Cooling Towers Work
An engineer-written explanation of how a cooling tower rejects heat from a water-cooled chiller plant by evaporating a small amount of water, including the key terms and the water and safety considerations in the UAE.
A cooling tower is the device that rejects the heat collected by a water-cooled chiller plant to the atmosphere. Warm condenser water from the chiller is cooled in the tower and returned to pick up more heat, completing the heat-rejection side of the cooling system. Towers are common on large UAE buildings because water-cooled chillers are efficient and need somewhere to dump their heat.
The clever part is that a cooling tower does not rely only on cool air — it uses evaporation. Evaporating a small fraction of the circulating water carries away a large amount of heat, which lets the tower cool water close to the outdoor wet-bulb temperature, often below the dry-bulb air temperature.
How it works
Warm water enters at the top. Condenser water leaving the chiller (commonly around 35 °C) is distributed over the top of the tower and trickles down through a large-surface-area packing called fill, which spreads it into thin films and droplets to maximise contact with air.
Air moves through the falling water. A fan (in a mechanical-draft tower) draws or pushes air through the fill in the opposite or cross direction to the water. As air and water meet, a small portion of the water evaporates, and evaporation removes heat from the remaining water — this is the dominant cooling effect, not simple air contact.
Cooled water collects in the basin. The cooled water (commonly around 29 °C) gathers in a basin at the bottom and is pumped back to the chiller condenser to absorb more heat, closing the loop. The difference between hot inlet and cooled outlet water is the range; how close the cooled water gets to the wet-bulb temperature is the approach.
Water is continuously lost and replaced. Evaporation, plus a small amount of windage/drift (droplets carried out) and deliberate blowdown (bleed-off to control mineral build-up), mean water must be topped up with make-up water. Because dissolved minerals concentrate as water evaporates, water treatment and blowdown control scaling, corrosion and biological growth.
Performance follows the weather and controls. Towers cool best when humidity is lower; fan speed and the number of operating cells are modulated to hold the required condenser water temperature efficiently. Good control balances fan energy, pump energy and chiller efficiency.
Main types
In the UAE
- Water is a precious resource in the UAE, so cooling tower make-up water use, blowdown and treatment are managed carefully, supporting water-efficiency goals under Estidama.
- Cooling tower water must be treated and maintained to control scaling, corrosion and biological growth (including Legionella risk), consistent with public-health and maintenance good practice.
- High coastal humidity reduces how cold a tower can make the water (a higher wet-bulb limits the approach), which engineers account for when sizing condenser water systems in the UAE.
How GPR applies this
GPR installs and maintains cooling towers as part of water-cooled chiller plants on Abu Dhabi projects, sizing them for the heat-rejection load and the local wet-bulb conditions, and integrating fan and cell control through the BMS for efficient condenser water temperatures. We set up water treatment, blowdown and drift control to manage scaling, corrosion and biological risk while limiting make-up water use, in line with UAE water-efficiency and maintenance good practice.
Frequently asked questions
What does a cooling tower actually do?
It rejects the heat collected by a water-cooled chiller to the atmosphere by cooling the condenser water, which is then returned to the chiller to absorb more heat.
How can a cooling tower cool water below the air temperature?
By evaporation. Evaporating a small fraction of the water removes a large amount of heat, allowing the water to approach the outdoor wet-bulb temperature, which can be below the dry-bulb air temperature.
What are range and approach?
Range is the temperature drop of the water across the tower (hot in minus cooled out); approach is how close the cooled water gets to the wet-bulb temperature — a smaller approach means better performance.
Why does a cooling tower need make-up water?
Water is lost to evaporation, a little drift, and blowdown (bleed-off to control mineral concentration), so fresh make-up water must be added continuously.
Why is cooling tower water treatment important?
Evaporation concentrates minerals and the warm, wet environment can encourage biological growth, so treatment and blowdown control scaling, corrosion and health risks such as Legionella.