Cooling tower

Wattson Explores The Central Cooling System

Previously, Wattson the Water Droplet explored the heating half of the Central Heating and Cooling Plant (CHCP). This time, he will be exploring the cooling side of the facility.

Wattson cooling

Cooling a building - The journey of a water droplet

UC Davis uses a closed loop of chilled water to cool buildings on campus. A network of underground pipes delivers chilled water throughout campus and into buildings’ mechanical rooms. Once there, the chilled water is piped into a cooling coil inside an air handling unit which blows air across the coil to cool the air down. The cooler air is then blown through ductwork into the rooms of the building, cooling them down. As the chilled water cools the air in the coil, it removes heat from the air and becomes warmer in the process. The warmer chilled water is then pumped back to the CHCP so it can be cooled again (or “chilled”) in the evaporator of a large machine called a chiller.

Chilled water distribution
Chilled water supply pipes.


Inside the chiller’s evaporator, the chilled water runs through long tubes where a low pressure liquid refrigerant is boiled off by the warmer temperature of the water. The evaporation process cools the water to its original low temperature, ready to be supplied back to the campus for cooling. Inside the chiller, the vaporized refrigerant is compressed inside massive compressors so that it can be turned back into liquid refrigerant inside a condenser, where the heat is expelled through a condenser water circuit that carries it out to a cooling tower.

The chiller's evaporator, where water is cooled.


In the cooling tower, heat from the warm water is rejected into the atmosphere. Thus, the heat from building occupants and building processes is moved to the outdoors, and the cooling cycle continues. In the summer, the evaporation cycle can cause clouds above the cooling towers as the warm air enters the atmosphere and condenses!

inside of cooling tower
The inside of the cooling tower.


Because this process is only transferring heat from one circuit to another, rather than generating heating or cooling, it is a highly efficient way to do cooling. Also, because the chilled water is a closed loop system, the water is reused and recirculated through the system so no chilled water is lost. Only the cooling towers lose water in the evaporation process but some of our cooling towers use recycled water to minimize the impact.

chilled water supply
Chilled water, supplied from the CHCP plant to the Earth & Physical Sciences Building.