Chilled Water AHU is a type of HVAC system that uses chilled water to cool and dehumidify the air. It typically consists of a fan, filters, heating and/or cooling coils, dampers, and controls. The chilled water is produced by a separate refrigeration system, such as a chiller, which cools the water to a temperature below the dew point of the air in the building. The chilled water is then circulated through the cooling coil in the AHU, where it absorbs heat from the air as it passes over the coil.