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

Z = 16

mZ = 3

mY = 3

0m

CASE 1 CASE 2

Z = 16

mZ = 3

mY = 3

0m

CASE 3 + dividing wallCASE 3

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

Questions?