The definition of a DOAS (Dedicated Outdoor Air System) is a system that is designed to provide a dedicated supply of fresh air to a building or space. This type of system is typically used in commercial buildings, such as office buildings, schools, and hospitals, as well as in residential homes. The DOAS is designed to provide a continuous supply of fresh air to the building, while controlling the temperature, humidity, and air quality. This helps to reduce the risk of airborne contaminants and improve the overall air quality in the building. The DOAS also helps to reduce energy costs by reducing the need for mechanical cooling and heating systems. The DOAS can also help to reduce the amount of outside noise entering the building, making it more comfortable for occupants. In addition, the DOAS can help to reduce the amount of pollutants entering the building, making it healthier for the occupants.