EastLink tunnels lead the way

VIDEO

EastLink is one of the first toll roads in the world to upgrade its tunnel ventilation system to dynamic ventilation on demand with partial portal emission. This upgrade has slashed the ventilation system’s electricity usage, reduced GHG emissions, and halved the audible noise from the ventilation system.

EastLink has twin 1.6 km tunnels, with three traffic lanes in each tunnel. The EastLink tunnels protect the environmentally sensitive Mullum Mullum valley above, reaching a maximum depth of 53 metres underground. Up to 115,000 vehicles drive through the EastLink tunnels in a single day.

The original tunnel ventilation system, commissioned when EastLink opened ten years ago, was designed to expel 100% of tunnel air, including pollutants from vehicles’ combustion engines, through two 45 metre high ventilation stacks.

Twenty-four smaller jet fans are located within the tunnels, to control air flow in through each tunnel portal, along the length of each tunnel, towards the base of each ventilation stack. The two stacks have a further ten larger ventilation fans to draw air up from the tunnels for expulsion at the stack tops.

Since the opening of EastLink, the speed of airflows within the tunnels and stacks was controlled in a traditional way, by switching individual fans on and off at pre-programmed times of the day. When switched on, a fan always operated at full speed.

EastLink identified a number of issues with this traditional type of tunnel ventilation system, including:

• Only operating ventilation fans at full speed is inefficient using more electricity than necessary, and produces higher operating noise levels.
• Switching an individual fan on and off at pre-programmed times of the day means that the fan is likely to operate for longer than is necessary.
• Toggling ventilation fans between fully off and fully on, and only operating fans at full speed increases wear and tear on components.
• Starting up a ventilation fan from fully off to fully on cause a step-change in noise, which makes morning start-ups more noticeable for nearby residents.

To address these issues, EastLink upgraded the ten large ventilation fans from fixed speed fully off / fully on operation to much more efficient self-regulating or closed loop variable speed operation.

EastLink corporate affairs and marketing manager Doug Spencer-Roy explained, “EastLink installed new impellers designed for quiet efficient operation within each of the existing ventilation fan housings, and new variable speed drive motors to regulate the rotational speed of the new impellers.”

For these works, each ventilation fan, weighing over 7 tonnes, was separately removed from and re-installed within the tunnel complex in delicate operations conducted during nights when traffic was lowest. Remarkably, almost no tunnel closures were required for these works. Traffic management was mostly limited to temporary lane closures while at least one lane remained operating.

EastLink also updated its ventilation control system to a closed-loop system using real-time data from air quality and air flow sensors to dynamically control the speed and number of fans required to meet traffic demand. Every few seconds, the updated control system adjusts the speed of each operating fan to ensure fan operation is fine-tuned in close to real-time.

Doug Spencer-Roy said, “EastLink’s tunnel ventilation system now responds dynamically, more efficiently and in close to real-time for the volume of traffic travelling through the tunnels, the vehicle mix such as the proportion of large heavy vehicles, and prevailing weather conditions such as wind speed and direction.”

In addition to the upgrade of the tunnel ventilation system to dynamic ventilation on demand, EastLink also introduced partial tunnel portal emission during day-time. (Since 2010, the EastLink tunnels had already been successfully operating tunnel portal emission at nights, under a change agreed that year with EPA Victoria.)

This means that during day-time, a limited amount of tunnel air is allowed to exit via tunnel portals, with the majority continuing to be dissipated via the ventilation stacks.

Doug Spencer-Roy said, “To verify that air quality standards in the local community have not been compromised through the introduction of these changes, we have located a temporary air quality monitoring station in a nearby residential area close to one of the tunnel portals.”

Following a pilot period which demonstrated the community benefits of dynamic ventilation on demand with partial portal emission, and that there has been no compromise to community air quality, EPA Victoria issued a new tunnel ventilation system licence to EastLink on 4 June 2018.

Doug Spencer-Roy said, “The results of the EastLink tunnels’ innovative dynamic tunnel ventilation on demand system and partial tunnel portal emission have exceeded our expectations, with huge reductions in electricity usage, greenhouse gas emissions and audible noise.”

• Ventilation system electricity usage has reduced by 68%, saving approximately 6.2 GWh each year.
• This electricity usage reduction will reduce GHG emissions from power stations by an estimated 9,000 tonnes CO2-e annually.
• Audible noise from the ventilation stacks has halved, confirmed by noise measurements, reducing noise for local residents.
• EastLink also expects savings in maintenance costs and longer lifespans for tunnel ventilation equipment.

Doug Spencer-Roy added, “Recently, a noise measuring team was conducting measurements near one of our ventilation stacks. The ventilation system is now so much quieter that the team needed to contact the EastLink control room to verify that the ventilation system was actually running.”

“EastLink’s successful implementation of dynamic tunnel ventilation on demand with partial portal emission was only possible through pro-active consultation with EPA Victoria, local councils and local residents – every step of the way.”

“EastLink recommends that other operators of major road tunnels consider whether similar changes to their tunnel ventilation system might provide community and business benefits without compromising their applicable air quality standards,” concluded Doug Spencer-Roy.

One of EastLink's two ventilation stacks:

Two of EastLink's ten large ventilation fans, which have been upgraded to variable speed drives with new impellers. These fans are now controlled dynamically using real-time data from air quality and air flow sensors:

A temporary air quality monitoring station has verified that air quality standards in the local community have not been compromised through the introduction of these changes: