General situation of the development of displacement ventilation

In recent years, a new ventilation method, displacement ventilation, has increasingly attracted the attention of designers and owners in my country. Compared with the traditional mixed ventilation method, this air supply method enables the indoor work area to obtain higher air quality, higher thermal comfort and higher ventilation efficiency. In 1978, a foundry in Berlin, Germany adopted the displacement ventilation system for the first time. Since then, the displacement ventilation system has gradually been widely used in industrial buildings, civil buildings and public buildings. Especially in the Nordic countries, about 60% of industrial ventilation systems now use displacement ventilation systems; about 25% of office ventilation systems use displacement ventilation systems.

Introduction to the principle of displacement ventilation

Displacement ventilation directs fresh air into the work area and creates a thin lake of air on the floor. Air lakes are formed by the diffusion of cooler fresh air. Heat sources (people and equipment) in the room generate upward convective airflow. Due to the buoyancy of the heat source, the fresh air flows to the upper part of the room and leads to the dominant airflow of the indoor air movement. Exhaust vents are placed at the top of the room and exhaust polluted air. The temperature of the fresh air fed into the room by the supply vents is usually lower than the temperature of the indoor work area. It sinks to the surface due to the density of the cooler air. The air supply speed of displacement ventilation is about 0.25m/s. The momentum of the supply air is so low that it does not have any practical effect on the prevailing air flow in the room. The cooler fresh air spreads over the entire indoor floor like pouring water and leads to an air lake. The thermal convection airflow caused by the heat source creates a vertical temperature gradient in the room. In this case, the air temperature of the exhaust air is higher than the indoor operating temperature. It can be seen that the dominant air flow of displacement ventilation is controlled by the indoor heat source. Therefore, this type of ventilation is also called heat displacement ventilation.