An upgrade to Melbourne’s EastLink tunnel ventilation system is one of the first updates of its kind, cutting electricity usage by two-thirds and resulting in impressive emissions reductions.
Greenhouse gas emissions dropped by 9,000 tonnes C02-e annually. The upgrade has also halved the audible noise from the ventilation system, and the ventilation system electricity usage has reduced by 68 per cent, saving approximately 6.2GWh each year.
The original tunnel ventilation system, commissioned when EastLink opened ten years ago, was designed to expel 100 per cent of tunnel air, including pollutants from vehicles’ combustion engines, through two 45m high ventilation stacks.
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’s engineers identified a number of issues with this traditional type of tunnel ventilation system.
To address these issues, EastLink upgraded the ten large ventilation fans from fixed speed fully off or fully on operation to much more efficient self-regulating or closed loop variable speed operation.
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.
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.
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.
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.