The Influence of Bend Angles upon the Performance of Passive Stack Duct Systems within Dwellings

Passive stack ventilation systems have been used for a number of years throughout the world. They were specifically mentioned within the 1995 revision of the Building Regulations for England and Wales as a means of compliance. BRE Information Paper 13/94 gives recommendations for the design of duct systems within dwellings that place restrictions upon the number and severity of bends that may be used. These restrictions limit the scope for the use of passive stack ventilation within dwellings. In this paper, computer simulation is used to investigate the influence of bend geometry upon flow rates. The results presented suggest that it may be possible to use properly formed bends of more severe angle than suggested by IP13/94, subject to ducts being designed and installed to an appropriate standard. The use of flexible spiral wound duct requires particular care in ensuring that bends are appropriately formed. Possible practical means of achieving appropriate bend shapes are discussed.