Cooling tower

A cooling tower is the large rooftop or plant-room structure that throws away the heat a chiller plant has collected from a building's chilled water — it does for a chilled-water/district-cooling system what the outdoor condenser does for a split AC. Warm water coming back from the chillers is cooled by evaporation as air is drawn through the tower, then sent round again to keep cooling the building. For a resident it's almost always the building or district-cooling provider's equipment, not yours — but it matters for two reasons: a poorly-maintained tower drops the whole plant's efficiency (and ultimately your cooling), and because it works by evaporating water in warm air, a neglected tower is the classic Legionella-risk point in large HVAC systems, which is why operators treat and monitor the water. If a whole building cools weakly, the plant and its towers — a chilled-water technician's territory — are upstream of any single flat's FCU.