500 Fan Coil Unit is a type of HVAC system that consists of a fan and a coil. The fan is used to circulate air over the coil, which can either be a heating coil or a cooling coil. The FCU is typically located within the occupied space of a building, such as in a ceiling or floor, and is connected to a central HVAC system. In a500 Fan Coil Unit, chilled water is circulated through the cooling coil, which removes heat from the air as it passes over the coil.