Explanation of static pressure, dynamic pressure, total pressure, and residual pressure

When choosing an air conditioner or fan, static pressure, dynamic pressure, total pressure, and residual pressure are often encountered. Based on knowledge of fluid mechanics. The vertical force exerted by a fluid on a unit area is called pressure. When air flows along the inner wall of a duct, its pressure can be divided into static pressure, dynamic pressure, and total pressure. The units are mmHg, kg/㎡, or Pa.

Static pressure:The pressure generated by the irregular movement of air molecules hitting the pipe wall. When calculating, the static pressure with vacuum as the zero point is called static pressure, and the static pressure with atmospheric pressure as the zero point is called relative static pressure. The air static pressure in air conditioning refers to relative static pressure, which is positive when it is higher than atmospheric pressure and negative when it is lower than atmospheric pressure.

Dynamic pressure:The pressure generated by the flow of air, as long as the air inside the duct flows, it has a certain dynamic pressure and is positive. Dynamic pressure=0.5 * Air density * Wind speed² .

Full pressure:It is the algebraic sum of static pressure and dynamic pressure. It represents 1m ³The total energy possessed by a gas (which can be positive or negative if calculated from atmospheric pressure).

Residual pressure:Residual pressure=total pressure - resistance of various devices within the system.

For example, an air conditioning unit consists of a return air section, an initial efficiency section, a surface cooling section, an intermediate section, a heating section, and a supply fan section. The resistance of each functional section is 20Pa, 80Pa, 120Pa, 20Pa, 100Pa, and 50Pa, respectively. Therefore, the internal resistance is 390Pa. If the external residual pressure is required to be 500Pa, the total pressure of the supply fan should not be less than 890Pa. If the external residual pressure is required to be 1100Pa, the total pressure of the supply fan should not be less than 1490Pa. High residual pressure is generally used for purification units, and the wind pressure is related to the selection of motor power. Generally, it should be based on the actual required residual pressure of the project. High residual pressure is not always a good thing.

Air conditioning units or fresh air handling units often install fans at the rear, with high outlet wind speed, high dynamic pressure, and low static pressure. In engineering, a soundproof static pressure box is often installed at the outlet to reduce dynamic pressure, increase static pressure, and also play a role in flow equalization and noise reduction.