Use of Non-Metallic Materials in Ventilation Airways- a review of aerodynamic performance and material requirements
Summary
A number of built enclosures in Crossrail stations, shafts and portals have been used for ventilation purpose. They are in the form of blockwork wall, spray concrete lining or reinforced concrete panels in plenums or airducts. Crossrail material and workmanship specifications for ducts and plenums and industry design, construction and test codes like DW143 and 144 are primarily developed based on sheet metal ductwork construction and may not be applicable to this situation.
In the study, a review was carried out to examine configuration and material finishes criteria that will have impacts on the aerodynamic performance of the enclosures to be used as airways. These criteria include surface roughness, change in cross section, leakage properties, construction and movement joints. The following design considerations were found to be important to allow the non-metallic airways to function effectively as an integral part of the ventilation system:
– Integrity of the airway structure against the design pressure force. These walls are not normally designed to take lateral loads.
– Air leakage because of the pressure differential between the enclosure and the surrounding and sealing of joints between the airway and other horizontal and vertical structures. Health and safety issues arising from the leakage have to be considered.
– Surface roughness and change in cross sections and their impacts on pressure drop calculation.
– Maintenance inspection and future replacement requirements throughout the asset life cycle.