Air flow(Q):(a.k.a. volume flow rate) the flow rate through the Cross-sectional area of pipe, the formula is: Q=60VA Q (Air flow)=m3/min V (Air velocity)=m/sec A (Cross-sectional area)=m2

(1) Standard temperature and pressure: for short "STP", in a condition of 20 degrees Celsius, 760mmHg absolute pressure, and 65% Relative Humidity. The weight for 1m3 of air is 1.2kg in this condition. (2) Absolute pressure of air: the sum of atmospheric pressure plus Gauge pressure. Usually expressed in units with kgf/m2 or mmaq. (3) Normal temperature and pressure: for short "NTP", in a condition of 0 degrees Celsius, 760mmHg absolute pressure, and 0% Relative Humidity. The weight for 1m3 of air is 1.293kg in this condition.

Pressure

(1) Static pressure(Ps): The pressure of a fluid exerts on a surface at rest. It is resulted by gravity and impeller in blower and fan, which can be measured directly. Usually expressed in units with kgf/m2 or mmaq. (2) Velocity pressure(Pv): (a.k.a. Dynamic Pressure) The pressure of a fluid in motion. Usually expressed in units with kgf/m2 or mmaq. (3) total pressure: The sum of Static pressure plus Velocity pressure. Usually expressed in units with kgf/m2 or mmaq. The total pressure is a fixed value for blower and fan, it is not changed when reducing the diameter of pipe.

Air pressure and temperature

Density of air changes with variances in temperature. If other conditions are fixed, the air pressure has to be adjusted by the following formula when variances in temperature: P= P'(273+t/293) (mmAq) Same reason, when variances in density of air: P=P'(1.2/γ) (mmAq) The P', t, andγare measured pressure, temperature, and density of air.

Air pressure and velocity

Pressure is proportional to the velocity. Pv=γ×(V2 / 2g) Pv: Velocity pressure(mmAq) γ: proportion of air(kg/m3) g: Acceleration of gravity(m/s2)=9.8 V: velocity(m/s)