What type of air conditioning system includes multi-zone and dual duct systems?

Central systems are designed to provide heating and cooling throughout larger spaces by using air ducts to distribute air to multiple zones or areas within a building. Multi-zone systems allow for separate temperature control in different areas, enhancing comfort and energy efficiency by tailoring heating and cooling to specific needs. Dual duct systems, on the other hand, utilize two ducts—one for hot air and one for cold air—allowing for precise control over the temperature in each zone.

In contrast, window units typically cool only the single room where they are installed, while portable units are movable and also serve individual rooms but do not connect to a duct system. Unitary systems, while comprehensive, generally refer to standalone units providing a specific function, rather than incorporating multiple zones or ducts necessary for the distribution of air to various parts of a larger building. Thus, the features of central systems make them the correct answer for this question regarding multi-zone and dual duct applications.