Breathability of Bag Air Duct

Breathability of Bag Air Duct

Understanding the Bag Air Duct Permeability

1. What does the Fabric Air Duct permeability mean?

• The main component of a fabric bag air duct is made of a special material—polyester fiber, and its permeability equals the air permeability of ordinary fabric.
• When the pressure in the duct is 125Pa, if the air permeability of 1 square meter of fabric air duct reaches 1 CFM (1 CFM = 1.68 M³/H), then the air permeability of the bag air duct is 1 Ch/T.
• The conversion unit can be expressed as follows: 1 CFM/ft² = 18 m³/H/m². In our country, we typically reduce the unit "m³/H/m²" to "mm/s". Thus: 1 CFM/ft² = 18 m³/H/m² = 5 mm/s.

II. The Importance of Selecting the Material for the Bag Air Duct

2. One of the characteristics of the bag air duct is that the airflow volume of the equipment transmitted through the bag air duct into the working area has two methods:

• First, through the infiltration of fiber materials (non-perforated method).
• Second, through the uniform distribution of jets around the air duct via openings or nozzles.

Among these methods, the most commonly used is the opening or nozzle method. The general amount of air infiltration can only be used to prevent the formation of condensation, which is not the reason why the duct does not produce condensation. Only 5%-10% of the total system's airflow volume (or less, except for pure infiltration mode ventilation) is used for this purpose.

If the air permeability is too high, it can lead to excessive heat exchange, causing a fixed cooling cost at high altitudes. Therefore, in different scenarios, different permeability materials (and different airflow paths) should be selected. For the same project, in different areas or at different installation heights, the choice of air outlet method should also vary accordingly.