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.

Design considerations

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)