Chilled-water loop

The chilled-water loop is the closed pipe circuit that carries cold water from the chiller plant (or the district-cooling supply) around a building and through every FCU and AHU, then back to be re-chilled — it's the bloodstream of a chilled-water system, the equivalent of the refrigerant loop in a split AC. Water leaves the plant cold, absorbs heat as it passes through each unit's coil, and returns warm. For residents this matters in two ways: problems in *your flat's branch* of the loop — a stuck control valve, trapped air, or a fouled coil — show up as weak cooling even when the central plant is perfectly fine (which is why the FCU is the lever you control); and the loop's supply temperature, set by the plant, caps how cold any FCU in the building can ever get. Balancing and treating the loop is a chilled-water systems specialist's work.