Commercial ventilation systems are used to control an indoor environment through air exchange. Any type of heating, ventilation, and air conditioning (HVAC) system used in a non-residential setting falls into this category. Forms of ventilation include natural ventilation, mechanical ventilation, and mixed mode ventilation. The different classes of ventilation are based upon how the system moves, or exchanges, the air. Each has its own specific purposes, as well as individual strengths and weaknesses.
The least expensive form of commercial ventilation is natural ventilation. This type relies on outside air pressure and temperatures to create changes in the indoor environment. Natural ventilation is achieved by opening the doors, windows, and vents of a building. This allows the outside air to enter the building and provides a steady exchange of air. The usefulness of this type of ventilation is affected by weather conditions.
Mechanical ventilation relies solely on the use of fans and other mechanical devices to force air exchange. It can be used in a single room or as a whole building ventilation system. This is the most expensive commercial ventilation system because it utilizes the greatest amount of equipment and results in higher operating costs.
Natural and mechanical ventilation systems are combined to create mixed mode ventilation systems. These hybrid systems rely on natural and mechanical elements to create a system that functions under a variety of conditions. A common example of mixed mode ventilation is the use of large exhaust fans in conjunction with open doors and windows in a factory building. The fan draws the outside air into the building through the doors and windows while pushing the indoor air out. This system is more effective than natural ventilation but offers less consistency than mechanical ventilation.
Engineers can design buildings that have a consistent negative or positive air pressure in order to ensure the success of mechanical ventilation. Whole building ventilation systems usually provide positive air pressure, meaning that the internal air pressure of the building is higher than that of the outside environment. Single room mechanical ventilation systems may be used as either positive or negative pressure systems. When used to create a negative pressure environment, the ventilation system pulls air out of a room, creating a vacuum to contain dangerous airborne contaminants, such as asbestos or sandblasting media.