How Does a Chilled Water AC System Work?

Whenever large premises such as factories, cinemas and shopping malls are involved, chilled water AC systems are often used as a large-scale cooling system. Most of us would have worn a jacket in these premises at some point or another, indicating the system’s efficacy.

Generally, these systems work efficiently and can be very versatile in application, as long as the system is insulated well. Still, most of us probably don’t fully grasp how they work. For that reason, we’ve described the process below.


This structure functions as a refrigerant to remove heat from the water. When the water leaves the chiller, it will have cooled down to about 7 degrees Celsius. Having passed the chiller evaporator, this cooled water will be pumped to circulate the entire building.

In the next separate structure, the compression chiller, refrigerant vapour heated up by hot water in a separate loop system is condensed into liquid using compressors. Here, the water will leave the condenser warmer by about 6 degrees Celsius.

While in the water-cooled condenser, the refrigerant liquid’s heat is transferred to the water via heat exchangers. This water flow heated by the refrigerant will then be piped to the cooling tower.

Cooling Tower

Due to its size, cooling towers usually are placed on top of buildings. In this structure, water heated up by the condenser in the compression chillers is cooled back down from about 35 degrees to about 29 degrees Celsius.

Once it’s cooled down, the water is ready to be sent back to the condenser again. Air is blown through the stream of water in this structure, causing some of the water to evaporate. However, the evaporation in turn effectively cools down the water stream.

Any water lost due to evaporation is replaced with additional water piping. The process within this water loop system is repeated to keep the water circulating the building chilled.

Fan Coils

To effectively distribute cool air throughout the building, water chilled in the chiller is piped into fan coil units. The fans in this unit have a large surface area to ensure that hot air is absorbed into the system.

Inside the unit, thermostats will detect and regulate how much cooling is required for the amount of heat received. After the chilled water receives heat from these units, it returns to the chiller at a temperature of about 13 degrees Celsius.

At the fan coil units, the air is now cooled and is redistributed back into the building.


Overall, there are two separate water piping systems. One water piping system passes through the chiller evaporator to get cooled down after absorbing heat from the fan coils, which in turn will cool down the hot air within the buildings.

Meanwhile, another system ensures that the refrigerant in the chiller evaporator stays liquidised and cooled down as much as possible so that water in the first system can cool down the building effectively.

In both systems, water circulates the piping continuously, getting heated up and cooled down again to produce cooler air until the set thermostat value has been reached.

Image via Pixabay CC0 License


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