What Is Natural Ventilation?

Natural ventilation refers to the way of using natural wind pressure, air temperature difference, and air density to ventilate and transport indoors, mines, or wells. Natural ventilation is relying on the wind pressure caused by outdoor wind and the heat pressure caused by the temperature difference between the indoor and outdoor air, which promotes air flow and enables indoor and outdoor air exchange in the building.

Natural ventilation under wind pressure

When the wind blows to the building, it will generate positive pressure on the windward side of the building because it is blocked by the building. At the same time, air flows around the sides and back of the building, creating negative pressure at corresponding locations. Wind pressure ventilation is to use the pressure difference between the windward and leeward sides of the building to achieve air circulation.

The climatic factors affecting wind pressure ventilation include: air temperature, relative humidity, and air velocity. Affecting the wind pressure and ventilation effect are the area of the building's air inlet and outlet, the opening position, and the angle between the wind direction and the opening.

Natural ventilation under hot pressure

Hot pressure is caused by the temperature difference between indoor and outdoor air. Due to the temperature difference, a density difference between indoor and outdoor occurs, and a pressure gradient appears along the vertical direction of the building wall. If the indoor temperature is higher than the outdoors, there will be higher pressure in the upper part of the building and lower pressure in the lower part. When orifices are present in these locations, air enters through the lower openings and exits from the upper. If the indoor temperature is lower than the outdoor temperature, the airflow direction is reversed. That is, ventilation is achieved by using the difference in air density and the height of the air inlet and outlet caused by the temperature difference between indoor and outdoor air.

Natural ventilation under the action of wind pressure and heat pressure

Natural ventilation in actual buildings is the result of the combined effect of wind pressure and heat pressure. The two effects sometimes reinforce each other and sometimes cancel each other out. Because wind pressure is affected by factors such as weather, outdoor wind direction, building shape, and surrounding environment, when wind pressure and heat pressure work together, it is not a simple linear relationship.

The design of buildings using natural ventilation should meet the following requirements: ^[2]

(1) For buildings with natural ventilation through the wind, the windward side of the building should be at an angle of 60 ° to 90 ° with the maximum wind direction in summer, and should not be less than 45 °. At the same time, the available spring and autumn wind directions should be considered to fully utilize natural ventilation.

(2) The layout of the building complex should pay attention to favorable natural ventilation factors, such as giving priority to staggered and oblique arrangements.

(3) Natural ventilation should use inlets, exhausts or sashes with low resistance coefficient, low noise, and easy operation and maintenance. Inlet and exhaust vents in severe cold regions should also consider thermal insulation measures.

(4) For buildings using natural ventilation, the calculation of natural ventilation should take into account the effects of heat pressure and wind pressure.