Tong chi to tell you what is the air volume and air pressure
wind pressure: for normal ventilation, need to overcome the resistance inside the fan ventilation trip, fan must have overcome the pressure of the air resistance, the change of the measured pressure value, called static pressure, the maximum static pressure and atmospheric pressure differential pressure. It is the gas pressure, the role of parallel to the surface static pressure is through hole measured perpendicular to the surface. What we need in the gas flow kinetic energy into pressure form called dynamic pressure.
to achieve the purpose of the supply air, need to have static pressure and dynamic pressure. Total pressure to the algebraic sum of static pressure and dynamic pressure, total pressure refers to the total pressure given by the fan in the increase, the fan of total pressure difference between exports and imports. In practical applications, the nominal maximum wind quantity is not the actual fan heat get delivery, air volume is big, does not represent the ventilation ability. Due to air flow, air flow in the flow path will meet fan heat collection or element block, the impedance will limit the free flow of air. Increase the air volume, air pressure will decrease. So there must be a best operating point, namely the fan performance curve and wind resistance curve intersection. In working point, the fan characteristic curve slope of the youngest, and the system characteristic curve of the lowest rate. Note that the fan static efficiency ( Airflow by air pressure present electricity) For the best. Sometimes, of course, in order to reduce system impedance, even use smaller fan, can also get the same air volume.