Interaction between station openings and environmental control systems
Chris Graham, Carlos Mesa, Mark Gilbey
WSP | Parsons Brinckerhoff in the UK
Context
• Review of recent work on a UK rail project
• Subsurface stations increasingly attractive due to external pressures
• Reduce or make better use of land take
• Potential for commercial over site development
• Constrained by tunnel alignment
• Concerns over public amenity
• Strong preference for natural ventilation of large spaces
• Natural lighting provided through large openings
Station geometry• Commuter rail service, shallow C&C construction
• Long rolling stock
• Train frequency demands multiple platforms
• Restriction on land take due to inner city location
• Desire for over site development improved land usage
• Visual effect of station for local stakeholders
• Provision of retail space
Problems faced• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow
Problems faced• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow
• Traditional louvres– limit light– resist natural ventilation– Difficult to mount horizontally– Adversely affected by wind if mounted vertically
• Clerestory vents– Glazing encourages natural lighting– Potential architectural feature– Utilises wind to aid natural ventilation
• Consideration of predominant wind direction• Considerations of challenging wind directions
Weather protection of openings
Weather protection of openings
• Wind conditions
• 2m/s to 12m/s
• 4 cardinal directions to look at effects under adverse wind conditions
• Assumed uniform wind profile, elevated vents
Problems faced• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow
Large irregularly shaped and dispersed openings• Clerestory vents not practical for large
openings• Egregious support steelwork
• Construction costs
• Maintenance burden
• Large openings typically require significant propping
• Unobstructed wind might recirculate smoke
• Beams might be used to control wind forces
• High aspect ration, hence transverse wind is not likely to be an issue
• Only studied longitudinal wind direction
• Adopted 12 m/s wind speed as a challenging case
• Given low level, atmospheric boundary layer profile used
Large irregularly shaped and dispersed openings
• Large beam spacings predicted negative flow (i.e. into station)
• Smaller beam spacings aid natural ventilation and encourage flow out of station.
• Improvements are predicted at beam spacing of greater 30m
• No disbenifit was predicted for smaller spacings
Large irregularly shaped and dispersed openings
• Station environment might be isolated from wind forces via active means
• Jet fans
• Air curtains
• Jet fans could be used to resist wind forces
• Modelled jet fans operating in the opposite direction to wind
• Results showed a viable concept
• Difficulties arise:
• Control system
• Noise
• Maintenance
• Cost
Problems faced• Exposed location – potential for strong wind interactions
• Weather protection of openings
• Large irregularly shaped and dispersed openings
• Interactions with civil structure
• Isolation of tunnel piston airflow
Isolation of tunnel piston airflow
• Prevent recirculation of warm tunnel air into adjacent bores
• Limit temperature pollution on platforms from warm tunnel air
• Introduce ambient air into station and outbound tunnel via openings
• Given high piston flows staggered openings were beneficial
• High velocity air overshoots openings immediately after portal
• Staggered openings limits recirculation between tunnels
• Further benefits realised by providing dividing wall between portals
Conclusions• Care should be given to the configuration and size of large openings
• Passive means can be used to– Provide wind force resilience
– Provide weather protection
– Maintain natural lighting and ventilation
• Structural elements may be complimentary to natural ventilation
• Jet fans could be used but concerns around practicality
• Location of openings at tunnel portals should consider both– Momentum forces (piston effect)
– Buoyant forces
– Mixing between adjacent tunnels