Building ventilation improves the air conditions of the indoor environment of buildings, which is divided into exhaust and air supply. The exhaust air discharges dirty air from the room, and the supply wind direction replenishes fresh air in the room.

The function of ventilation is to discharge indoor air and remove indoor heat, humidity and harmful substances. The function of air supply is to send outdoor air, improve the freshness of indoor air, and also dilute and replace indoor heat, humidity and harmful substances.

According to the different conditions and requirements of the indoor environment, building ventilation can exhaust and supply air at the same time, or one of them.

Building ventilation can be used for life or production, which is also called industrial ventilation. A series of equipment, pipelines and devices used to realize ventilation and air supply are collectively referred to as ventilation systems.

Ventilation is divided into natural ventilation and mechanical ventilation according to power. Natural ventilation uses natural forces to promote air flow, while mechanical ventilation uses powered machinery such as fans to force air flow.

The natural forces of natural ventilation are divided into thermal pressure and wind pressure. The thermal pressure is generated by the density difference of indoor and outdoor cold and hot air, and the wind pressure is generated by the pressure difference of air on the windward side and leeward side.

Mechanical ventilation is divided into general ventilation, local ventilation and mixed ventilation according to the scope, which ventilate all, local or combined indoor space respectively.

Comprehensive ventilation ventilates all indoor spaces to completely eliminate or dilute indoor heat, humidity and harmful substances; Local ventilation is aimed at local parts with heat, humidity or harmful substance control requirements. The common ones are factory post air supply, laboratory local exhaust hood, etc.