Ventilation for Healthy Living
4. Ventilation Performance
The ventilation performance is largely affected by the installation conditions. Optimum 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)" .
4.1 Air Volume
Air volume equals the volume of air exhausted (or supplied) by the unit in a given period, and is expressed in CFM or m
4.2 Wind Pressure
When a piece of paper is placed in front of a fan then released, the piece of paper will be blown away. The force that blows the
paper away is called wind pressure and is normally expressed in inH
O. Wind pressure is divided into the following three types:
4.2.1 Static Pressure
The force that effects the surroundings when the air is contained such as in an automobile tyre or rubber balloon. For example,
in a water gun, the hydraulic pressure increases when pressed by a piston. If there is a small hole, the water is forced out of
that opening. The pressure of the water is equivalent to air static pressure. The higher the pressure, the farther the water (air)
can be forced out.
4.2.2 Dynamic Pressure
The speed at which air flows; for example, the force at which a hurricane presses against a building.
4.2.3 Total Pressure
The total force that wind has, and is the sum of the static pressure and dynamic pressure.