A chilled-water system uses chillers to cool water, then pumps that water to coils in air handlers, fan-coil units, or process equipment. The water absorbs heat from the building and returns to the chiller. Heat is rejected outdoors through cooling towers or air-cooled condensers.
This is different from a packaged rooftop unit, which cools air directly with refrigerant at the equipment. Chilled water centralizes cooling so many air handlers—or several buildings—can share a plant.
Why large buildings use it
Redundancy, efficiency at scale, flexible air-side systems, and the ability to add buildings to a loop. Hospitals in Melbourne and Titusville, campuses, and industrial plants use chilled water because the alternative is a roof full of unrelated machines with no shared backup.
What has to be designed
Water temperatures, flow rates, pumping arrangement, pipe sizing, control valves, and sequences. A chiller catalog sheet is not a system. Thermal storage can be added so the plant makes cooling at one hour and uses it at another.
If you are asking whether a building needs chilled water, the usual triggers are size, diversity, mission criticality, and campus distribution—not the brand of the air conditioner.