WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities
Chilled water systems remove heat by passing recirculated cold water through equip-
ment. They are often used in place of single-pass cooling because the water is recir-
culated, rather than being discharged, to the drain. Chilled water systems are often
used to cool air passing through air handling units, but they can also be used to cool
a number of systems, including:
Water can be used to transfer heat loads within a chilled water system in two ways, as
illustrated in Figure 6-4. First, water can be recirculated as a heat transfer fluid be-
tween the chiller and the equipment to be cooled. This water is contained in a closed
loop, and no water is gained or lost when the system is operating properly. Second,
the chiller, or refrigeration unit, might use water or air to remove heat from the refrig-
eration condenser. These types of chillers are referred to as water-cooled or air-cooled
A chiller’s cooling capacity is measured in tons of refrigeration, a metric used to repre-
sent the amount of heat that can be extracted by the system in a 24-hour period.
Small systems (i.e., 40 to 50 tons of refrigeration and below) are often designed as
air-cooled systems because they are less expensive, although the energy consump-
tion of air-cooled systems is usually significantly higher, especially as the systems
approach 500 tons. In addition, the space required for air-cooled systems greater
than 500 tons becomes impractical in many applications. Since air-cooled systems are
used in limited applications and use air instead of water as the cooling mechanism,
they are not the focus of this section.
Water-cooled units tend to be more energy-efficient than air-cooled units, particu-
larly in larger facility applications.
As shown in Figure 6-4, there are four main stages of operation in a water-cooled
chilled water system:
First, chilled water at a temperature between 38° and 45°F is pumped through
heat exchange units to transfer heat from equipment. By removing heat, the
chilled water temperature typically rises 10° to 20°F.
Chilled Water Systems
Koeller and Company and Riesenberger, James. January 2006.
A Report on Potential Best Management Practices—Commercial-Industrial Cooling Water Efficiency
Prepared for the California UrbanWater Conservation Council. Page A-5.