Types of textile ducting
In the main there are two types of textile ducting: The first being "low impulse" and the second "high impulse". The former type is a permeable woven textile through which the air diffuses at a very low velocity, typically 0.07-0.11m/sec.
The "high impulse" type takes the form of a non-permeable material into which 5mm diameter holes are strategically punched in specifically designed patterns, these hole patterns are critical in achieving the required air distribution and the correct level of comfort specified for the occupied zone.
Although, the air is discharged through the surface of the textile ducting at very low velocity this property alone is not enough to guarantee a draught-free environment. Similarly, for high impulse type of ducting, careful calculations are needed to ensure that the air velocity is in accordance with the comfort required.
These calculations refer to the throw, penetration, relative air density, hole pattern, duct static pressure, and the orientation of holes.
It is for this reason that an assessment for the area must be made, and the following parameters evaluated: cooling/heating W/m2 length duct; cooling/heating W/m2 of floor area; air volume per metre length duct; room temperature; supply air temperature; positioning of the ducting; required room conditions; activity of room occupants; clothing of room occupants; purpose of the room; objectives of the cooling/heating capacity.
With this information, reference should then be made to the information contained in Table A in order to determine the room category.
If this design procedure is not followed then the project will inevitably comprise either too little ducting or too much textile ducting, neither of which is desirable and most probably the quality of the room environment will suffer.
(Extract from MASTERCLASS: Textile-based air distribution Part 34 Published on 1 - October - 2008)