The Emerald
The Emerald is a 20 storey residential apartment building with a large above and below ground car park. At first glance, the building is characterised by a distinct flowing façade reminiscent of the gentle water ripples which are viewable, across the road from the site, on Albert Park Lake.
ACG were assigned the task of performing the post tender detailed design calculations and installation the building’s HVAC systems. The apartment systems were typical of a class 2 high rise. However, the car park ventilation system, which on its surface appeared familiar, posed an interesting challenge.
The car park, which was comprised of 3 below ground basement levels and 4 above ground levels, was provided with mechanical exhaust via two 1250mm diameter axial fans working in parallel. Having a total of 7 floors of car park served by a single 2 fan exhaust fan arrangement meant that a typical AS1668.2 control system would be susceptible to inefficient operation.
The challenge
During normal use, there is a non-uniform demand for ventilation on each of the car park levels. If the system is controlled via a typical AS1668.2 control scheme, the exhaust system will respond to a call for a higher ventilation rate on one floor by increasing the ventilation rate uniformly to all floors. This would mean that the fans are almost always running at a much higher ventilation rate than is required by the actual total ventilation demand.
This issue was further highlighted by the fact that the above ground car park floors had open facades which would have provided compliant natural ventilation, if not for their close proximity to the property boundary.
To achieve compliance, a full car park ventilation system needed to be installed to 3 of the above ground levels, although in practice these levels were unlikely to have a demand for mechanical ventilation due to the extensive façade openings. During peak hour conditions, this would mean that over 12,000 L/s of mechanical ventilation would be provided to what was is, in reality, 3 levels of open deck car parking.
The solution
An intelligent control system which provided the ability to independently vary the exhaust rate to each floor was required. Given that the system was served by a single twin exhaust fan arrangement, this was achieved via motorized dampers located at the branch take offs running to each of the main zones.
Each of the motorized dampers’ positions was dictated by the highest CO concentration detected in the corresponding zone and dedicated in duct pressure sensors, which were calibrated during commissioning to provide feedback to the control system of the air flow rate within the exhaust duct.
A relatively simple and cost effective addition to the car park ventilation control system requirements of AS1668.2 resulted in high running cost savings to the client. The system’s energy consumption is currently being monitored to provide a long term profile of the actual cost savings.
As always, the commissioning and calibration phase as the pivotal moment in the overall process, during which some important lessons were learned. Accurate calibration of pressure sensors and fine tuning of the control system by ACG’s engineering team were critical to finishing the project with the ventilation system operating efficiently and as designed.