Heating, ventilation, and air conditioning (HVAC) systems are designed to achieve the environmental requirements of the comfort of occupants and a process. HVAC systems are the backbone of building mechanical systems that provide thermal comfort for occupants accompanied with indoor air quality. HVAC systems can be classified into central and local systems according to multiple zones, location, and distribution. Primary HVAC equipment includes heating equipment, ventilation equipment, and cooling or air-conditioning equipment. Central HVAC systems locate away from buildings in a central equipment room and deliver the conditioned air by a delivery ductwork system. Central HVAC systems contain all-air, air-water, all-water systems. Two systems should be considered as central, such as heating and cooling panels and water-source heat pumps. Local HVAC systems can be located inside a conditioned zone or adjacent to it and there is no requirement for ductwork. Local systems include local heating, local air-conditioning, local ventilation, and split systems.