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CHAPTER 1 G Ventilation for Healthy Living
4. Ventilation Performance
The ventilation performance is largely affected by the installation conditions. Ample performance may not be achieved unless
the model and usage methods are selected according to the conditions.
Generally, the ventilation performance is expressed by "Air volume" and "wind pressure (static pressure)", and these are
necessary when considering ventilation.
4.1 Air volume
Air volume expresses the volume of air exhausted (or supplied) by the unit in a given period. Generally, this is expressed as
3
m
/hr (hour).
4.2 Wind pressure
When a piece of paper is placed in front of a fan and let go, the piece of paper will be blown away. The force that blows the
paper away is called the wind pressure, and this is normally expressed in units of mmH
O or mmAq {Pa (Pascal) in SI unit
2
system: 1 mmH
O = approx. 9.8Pa}. The wind pressure is divided into the following three types:
2
4.2.1 Static pressure
This is the force that presses the surroundings when the air is still such as in an automobile tyre or rubber balloon. For
example, in a water gun, the hydraulic pressure increases when pressed by a piston, and if there is a small hole, the water
sprays out with force. The pressure of this water is equivalent to the static pressure for air. The higher the pressure is, the
further the water (air) can be sprayed.
4.2.2 Dynamic pressure
This expresses the speed at which air flows, and can be thought of as the force at which a typhoon presses against a building.
4.2.3 Total pressure
This is the total force that wind has, and is the sum of the static pressure and dynamic pressure.
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