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This module considers the design and application of textile-based air distribution systems Textile-based ductwork distribution systems
Examples of the application of fabric- or textile-based air distribution stretch back into the mid-20th century, where simple, inflating cotton bags (or ‘socks’) were attached to the end of metal spigots to provide a means of supplying large amounts of ventilation air. Although, originally, applications tended towards industrial locations where the lightweight, machine-washable ducts were particularly attractive, such as food preparation areas, slaughterhouses and laboratories (see Figure 1), they have since seen wider adoption in commercial and industrial installations, such as offices, workshops, schools, shops and showrooms. Despite their increasingly widespread use,
there is little design guidance from CIBSE or ASHRAE. However, several manufacturers – many of whom evolved in Europe – have developed respectable design and installation guides as part of their sales offering, with each system requiring individual design, dependent on the room characteristics, supply air volumes and temperatures. The cotton used in the early applications
was quickly found to absorb water and, owing to its organic nature, potentially harbour bacteria and moulds, so it was quickly replaced by polyester and oil-based synthetic fibre that became widely available in the 1950s. The polyester employed is a UV and crease-resistant material that can be coloured, providing a robust, flexible fabric
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Figure 2: Circular permeable textile ‘low impulse’ supply – cooling ∆T of 0K, >5K, <3K
Figure 1: Example of a laboratory using a low impulse permeable textile half circular (‘D’-shaped) ventilation system
that, when woven with other specific yarns, make it fire retardant. At the end of the useful life, the fibres can also be re-processed into recycled polyester materials. Textile ducting is applied using both permeable and non-permeable materials. Permeable materials may be categorised by their dust-holding capacity. This is not to infer that the ducts should be used as a filter – textile-based systems require filtration in the air handling unit like more traditional metal duct systems. However, some particulate matter will pass into the supply air – the fabric’s dust-holding capacity and the quality of the centralised filtration will influence the frequency of cleaning. High dust capacity (HDC) materials are made of staple fibre yarns capable of carrying a large amount of dust without blocking
Figure 3: Circular non-permeable fabric ‘high impulse’ supply ducts with directed nozzles
Figure 4: Circular permeable textile ducts with the addition of directed nozzles for diffusion and projection
the airflow through the material. Low dust capacity (LDC) materials are typically woven of multifilament warp yarns. These fibres are plain and smooth, with a small surface compared to that of the staple yarns. In weft direction (crosswise), the same staple yarns are used as for the HDC fabric; however, the
May 2013 CIBSE Journal 47
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