Tunnel Ventilation System Design and Air Quality

Peter Gehrke and Andrew Purchase

Summary of Our Input

Primarily - how does the choice of in-tunnel criteria and operational strategies affect the system design and required infrastructure?

This affects:

• Exhaust/Supply fan capacity

• Numbers and size of jet fans

• Requirements for smoke ducts

• Requirements for ventilation tunnels

• Longitudinal or transverse ventilation

• Power usage

• Capital and maintenance costs

Background Experience - Road Tunnel Design

• M5 East – Sydney (4km, design review)

• Cross City Tunnel – Sydney (2km, parallel design)

• Lane Cove Tunnel – Sydney (3km, tender design)

• Eastlink Tunnel – Melbourne (2km, design reviewer)

• Clem7 (North South Bypass Tunnel) – Brisbane (5km, system • Clem7 (North South Bypass Tunnel) – Brisbane (5km, system

design)

• Airport Link Tunnel – Brisbane (6km, system design)

• PR53 Highway Tunnel – Puerto Rico (1km, system design)

• Victoria Park Tunnel – Auckland (460m, system design)

Tunnel Ventilation System Design – Factors

Considered

• Vehicle emission factors

• Portal emissions

• Smoke control requirements

• Carbon monoxide (CO)

• Oxides of nitrogen (NO /NO )

• Vehicle heat - temperature

• In-tunnel air velocity

• Controllability

• Oxides of nitrogen (NOx/NO2)

• Carbon Dioxide (CO2)

• Sulphur Dioxide (SO2)

• Visibility - particulate matter (PM)

• Volatile Organic Compounds (VOCs)

Vehicle Emission Factors

• In Europe and Australia, emission factors are determined from

PIARC tables correlated to vehicle classes.

• Post construction measurements indicate that PIARC, as applied in

Australia, adequately predicts emissions.

• New Zealand has a Vehicle Emissions Prediction Model (VEPM).

• VEPM documentation outlines that the model is best suited for 1km • VEPM documentation outlines that the model is best suited for 1km

resolution over a period of 1 hour and is not suitable for predicting

instantaneous emissions. Emissions as a function of speed are

provided but not as a function of grade.

• Tunnel ventilation design considers short time scales and also

grades. VEPM applied to tunnels needs consideration.

• Risk that conservative emission inputs results in overdesign of

systems.

Portal Emissions

• No portal emissions criterion eliminates pollutant dispersion at portals

with exhaust fans and stacks required to disperse emissions.

• Consideration should be undertaken for individual projects. Some

portals can effectively disperse pollutants – PIARC/M5 East experience.

• Typically the piston effect can generate sufficient airflow for ventilation.

For no portal emissions this often results in running jet fans against the For no portal emissions this often results in running jet fans against the

traffic flow. There is significant energy usage required.

• From a sustainability perspective, consideration should be given to

allowing portal emissions at night or when traffic volumes are low.

• Allowing portal emissions during traffic incident can in some cases

reduce system capacity

Smoke Control

• Smoke control requirements can set ventilation sizing

– Emissions – affects operating and capital costs (portal emissions)

– Smoke control – affects capital costs (essential, but rarely used)

• Strategy

– Longitudinal or a smoke exhaust duct

– Operator response and traffic management– Operator response and traffic management

• Design fire size – specific for each tunnel

– Vehicle types (cars, trucks, DGVs)

– Concession for deluge

• Quantify appropriate design fire size by risk assessment (don’t just select the biggest fire).

• Design fire size affects number of jet fans, sizing of exhaust fans and ventilation pathways.

Tunnel Geometry/SystemSupply/Exhaust

(m3/s)1 Jet FansPower (MW)2 In-Tunnel Criteria

Eastern Distributor

Sydney

1.6km, twin bore, 3 lanesStacks at each tunnel end

Portal emissions allowed off peak960 exhaust 46 (60kW) 5

CO – 100ppm peakCO – 87ppm 15 minNO2 – 1ppmVis – 0.005m-1-0.009m-1

M5 East Sydney

4km, twin bore, 2 lanesOne centre stack

‘Circulatory ventilation’

450 supply1000 exhaust

119 (mostly 12

CO – 87ppm 15 minNO2 – NA

Background Experience - Road Tunnel DesignSystem Examples – Australian Road Tunnels

Sydney ‘Circulatory ventilation’No portal emissions

1000 exhaust1000 crossover

(mostly 45kW)

NO2 – NAVis – 0.005m-1-0.009m-1

Cross City Sydney3

2.2km, twin bore, 2 lanesStack at one end

Crossover ventilationExhaust tunnel for traffic incidents

No portal emissions

800 exhaust400 crossover

450 exhaust tunnel54 (60kW) 6

CO – 87ppm 15 minCO – 50ppm 30 minNO2 – 1ppm ?Vis – 0.005m-1-0.007m-1

Lane Cove Sydney3

3km, twin bore, 3 lanesStacks at each end

Mid-tunnel supply /exhaust with ventilation tunnel

No portal emissions

1100 supply2600 exhaust

120 (75kW)

17

CO – 87ppm 15 minCO – 50ppm 30 minNO2 – 1ppm ?Vis – 0.005m-1-0.007m-1

Notes:

1. Flow values are rounded installed capacity. Not all this capacity may be used at one time.

2. Power figures are estimated totals.

3. In-tunnel CO criterion was made more stringent by RTA based on M5 East air quality perceptions

Tunnel Geometry/SystemSupply/ Exhaust

(m3/s)1 Jet FansPower (MW)2 In-Tunnel Criteria

Eastlink Melbourne

2km, twin bore, 3 lanesStacks at each endNo portal emissions

1500 exhaust120

(75kW)17

CO – 150ppm peakCO - 50ppm 15 minNO2 – 1.5ppmVis – 0.005m-1-0.009m-1

Clem7/North South Bypass

4.8km, twin bore, 2 lanesStacks at each end

1500 exhaust1000 extra exhaust 119 10 vent

CO - 70ppm flowing trafficCO – 90ppm slow traffic

System Examples – Australian Road Tunnels

South Bypass Brisbane

Stacks at each endSmoke exhaust ductNo portal emissions

1000 extra exhaust available via smoke duct

119(40kW)

10 vent6 smoke

CO – 90ppm slow trafficNO2 – 1ppmVis – 0.005m-1-0.007m-1

Airport Link Brisbane

6km, twin bore, 2/3 lanesStacks at each end plus central stack

Smoke exhaust ductNo portal emissions

2300 exhaust800 extra exhaust

available via smoke duct

170(30kW)

10 vent9 smoke

CO - 70ppm flowing trafficCO – 90ppm slow trafficNO2 – 1ppmVis – 0.005m-1-0.007m-1

Notes:

1. Flow values are rounded installed capacity. Not all this capacity may be used at one time.

2. Power figures are estimated totals.

3. In-tunnel CO criterion was made more stringent by RTA based on M5 East air quality perceptions

Effect of In–Tunnel Criteria

• CO, NOx and visibility (PM) considered.

• A ‘typical’ tunnel used as a base – single bore long tunnel, longitudinally

ventilated with no portal emissions.

• Criteria modified to estimate relative change in ventilation requirements -

numbers of jet fans and exhaust stack capacity.numbers of jet fans and exhaust stack capacity.

• Vehicle emissions were based on Australian factors (cleaner fleet than

NZ), however relative changes would still be valid.

• Figures based on assessing requirements for all flowing traffic speeds.

• Traffic incidents causing prolonged exposure are not considered.

Carbon Monoxide (CO)

CO criterion

Design driverExhaust rate

(m3/s)Number of jet

fans

Estimated power (MW)

90ppm Max 5km/h 300 - 400 40 3.5

70ppm Max 5km/h 400 - 500 70 5.5

50ppm Max 5km/h 500 - 600 180 1350ppm Max 5km/h 500 - 600 180 13

50ppm 30min exposure (excluding

traffic incidents)

5km/h 300 - 400 60 4.5

Notes:

1. Approximate values are provided to assess relative changes.

2. Power figures are estimated totals.

3. Only one tube assessed.

4. Fire cases and controllability not assessed.

Nitrogen Dioxide (NO2) and Visibility

NO2

criterionDesign driver

Exhaust rate (m3/s)

Number of jet fans

Estimated power (MW)

1.5ppm Max 20-40km/h 200 – 300 10 1.5

1ppm Max 20-40km/h 300 - 400 20 2.0

0.5ppm Max 20-40km/h 600 - 700 120 100.5ppm Max 20-40km/h 600 - 700 120 10

VisibilityCriterion

Design driverExhaust rate

(m3/s)Number of jet

fans

Estimated power (MW)

0.007m-1 20km/h 200 - 300 12 1.5

0.005m-1 10-20km/h 300 - 400 30 3

0.003m-1 10-20km/h 600 - 700 120 10

Notes:

1. Approximate values are provided to assess relative changes.

2. Power figures are estimated totals.

3. Only one tube assessed.

4. Fire cases and controllability not assessed.