101 Miller Street, North Sydney. Photo: Anthony Fretwell

3 March 2011 –CASE STUDY: The landmark former Optus Building in North Sydney building has achieved a five star NABERS energy rating following its $40 million refurbishment in 2007-2008.

The property at 101 Miller Street, owned by Mirvac Funds Limited and Eureka Funds Management, now has a three Mega Volt Amps trigeneration system, one of the largest trigeneration systems installed in a commercial office building in Australia.

The building was occupied by Optus, a single tenant, from the completion of construction in 1992 for 15 years. The telco’s decision to vacate the premise from mid 2007 presented “both a significant challenge and rare opportunity for Mirvac to undertake a large scale refurbishment of the building to maintain its landmark status and to achieve unprecedented levels of greenhouse gas efficiency from a 15+ year old building,” a spokesperson for Mirvac said.

Prior to refurbishment, the building improved its NABERS rating from three stars to 4 stars “through careful tuning and management of the building air conditioning and control systems. This was considered to be the optimal performance that could be gained from the existing plant.”

Mirvac partnered with Cogent Energy Pty Ltd to design, install and operate the trigeneration plant. The installation consists of 2 x 1.2 megawatt natural gas generators and 2 x 750 kw absorption chillers and associated control and switchgear, providing peak power of 2.4 mw and 1500 kw of cooling capacity.

The waste heat “by-product” from the power generation can be harnessed to provide both heating and cooling this has the potential to save up to 3,500,000 kilograms of Co2 of base building emissions equivalent a year compared to current best practice for a building of its size.

Despite the plant’s size being limited by the need to ensure the natural gas generator maintained an efficient operating load, benefits to future tenants and the surrounding areas will include:

  • Parallel import operation of the natural gas generator plant to ensure backup from the grid in case of natural gas generator failure
  • Targeted best practice five star NABERS energy performance
  • Lower power costs for the building owner and tenants
  • Reduction in North Sydney peak demand by up to three MVA @ 0.8 power factor, reducing stress on power supplies in the area.

The property’s mechanical services have been upgraded to reduce energy usage, maintain comfort and flexibility while retaining the considerable investment in large parts of the original mechanical services installation, the owners.

A number of changes were made to the building’s mechanical services to increase energy efficiency, including:

  • Considerable use of variable speed drives
  • Upgrade and improvement of the outside air system
  • Cooling water chillers and cooling towers upgraded to increase energy efficiency and reduce water consumption
  • Additional air control dampers have been installed to allow after hours zone control down to quarter floors
  • A new building management system has advanced control features and extensive energy sub-metering to maximise the potential of the upgraded mechanical services

Mirvac Asset Management collaborated with the NSW Department of Environment, Climate Change and Water to allow buildings with cogeneration and trigeneration systems installed to be rated under the NABERS protocol.

Other sustainability achievements for the project include a five star Green Star office design rating.

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