For normal ventilation, need to overcome the resistance inside the fan ventilation trip, fan must have overcome the pressure of the air resistance.Values measured pressure changes are called static pressure, the maximum static pressure and atmospheric pressure difference.It is the gas pressure, the role of parallel to the surface through the perpendicular to the surface of the hole were measured. 
The gas flow required is called dynamic pressure in the form of kinetic energy into pressure.To achieve the purpose of the supply air, need to have static pressure and dynamic pressure.Total pressure is the algebraic sum of static pressure and dynamic pressure.The stronger the wind pressure, the greater the fan air supply ability.1, the static pressure units
N: Newton, 1 N = 0.101097 Kgf
Pa: Pascal, Pa = N/m ^ 2
MmAq: Aq = Aqua (water)
Say again mmAq mmH2O;1 mmaq = 1 kg/m ^ 2
ATM: atmospheric pressure;A is equal to atmospheric pressure at 0 ℃ 760 MMHG pressure drying condition.
Because mercury weight is 13.5947 times of water, so the atmospheric pressure is equal to 10332 mmh2o pressure
Bar: 1 bar = 0.00001 Pa = 10-5 pa2, static pressure, air quantity in table 3
Blower unit time of inhaled Air flow is called Air quantity, Air volume, Air quantity, usually in Q (m * 3 / min) for the amount of gas, called on the inhale Air volume, the occasion of fan is also called Air volume.(Capacity) gas, according to its volume, pressure, temperature and change so that spit out the air quantity, be sure to remember the place of pressure and temperature, therefore calls to inhale air quantity.4, the standard state air:
20 ° C temperature, atmospheric pressure, 760 MMHG, moist air humidity of 65% for the standard air, this time the weight of per unit volume of air (also called than weight) for L2Kg/m * 35, benchmark state air:
O ° C temperature, atmospheric pressure, 760 MMHG, moist air humidity of 0% for the standard air, this time the weight of per unit volume of air (than) weight of 1.293 Kg/m * 3.In order to * 3 Nm/min said.