All-water systems use a single chiller plant, or chiller and boiler, to produce water, which is then pumped around the building, usually, to fan coil units. A fan blows air over a coil that contains the water, which in turn cools or heats the rooms air. The heat rejected from the room to the water is then pumped back to the chiller unit where it is rejected by a condenser to the external air. The water is then heated or chilled again and pumped back to the rooms units.
