Recognising impending changes to the way in which NABERS Energy ratings are to be calculated, Cromwell more recently engaged A.G. Coombs Advisory to investigate the impact of the building’s 1900kVA gas-fired cogeneration plant on its environmental ratings.

“Our feasibility study found the use of the cogeneration system’s absorption chiller to provide cooling as a supplement to the building’s chilled water plant did not provide significant reduction in emissions compared to the electric chiller plant, largely as a result of the auxiliary systems required to run the absorber,” says John Bourne, Leader – Sustainability at A.G. Coombs Advisory.

The study took into account the maintenance and life cycle of the plant, the standby power demands of the building, the changing cost of energy and a decarbonised electricity grid, in particular the upcoming changes to the NABERS Energy rating emissions factors – both short and long term.

“It used to be that by using natural gas to generate power on site, carbon dioxide (CO2) emissions were approximately halved compared to the Queensland electricity grid,” says John. “But as more renewables contribute to the electricity grid, generating locally with gas is no longer as carbon efficient.”

A.G. Coombs Advisory found that by removing the cogeneration set and replacing it with a magnetic bearing, water-cooled electric chiller and standby diesel generator to power essential services offered the potential to improve HQ North tower’s NABERS Energy rating to a market-leading 6 stars. The use of a HFO (R1233zd) refrigerant further reduces the Scope 1 emissions from the site.

Additionally, the plant’s replacement reduces plant operational costs and allows the optimisation of plantroom space through careful design, thereby increasing the space afforded to the onsite facility management team. The use of a diesel generating set for standby power greatly simplifies the operation and maintenance of the plant and increases the reliability of the system.

The sizing of the new electric chiller was critical to the success of the project. The new chiller needed to replace the absorption chiller’s capacity while still providing a high-efficiency alternative to the existing low load chiller.

Accepting these recommendations, Cromwell engaged A.G. Coombs Advisory to write the specification for the replacement of the cogeneration plant, and provide technical support to the tender process. Cromwell awarded the project to A.G. Coombs under a traditional design and construct (D&C) contract, with A.G. Coombs Advisory staying on in a technical capacity for the client.

The project commenced in mid-2022 with the building’s cogeneration plant decommissioned and the system’s absorption chiller and emissions treatment system removed.

A waste minimisation strategy saw many components of the plant reused, including the gas powered generator which will be used in outback Australia, the urea which is being used in another trigen plant, the lithiumbromide which is being reused in another absorption chiller overseas and various other components which are being retained as spare parts to extend the life of other plant. The absorption chiller, along with other components including redundant cable, pipework and flues were recycled.

The works presented a major logistics challenge to minimise disruption to the building and tenants, and safely remove the heavy plant. With the existing suspended slab floor requiring back-propping, the entire removal works were completed across one weekend.

Through careful cut-over planning, the complete shutdown of services has been limited. A temporary generator provided standby power to essential services for the duration of the changeover, until the new diesel generator and associated systems were complete.

“This has been one of the most complex jobs I’ve ever managed,” says Gareth McCrystal, Project Manager at A.G. Coombs. “Working side-by-side with the A.G. Coombs Advisory team and leaning on the technical expertise of the broader Group, has been of enormous benefit.”

Additionally, Gareth says having the right trade partners in place has been crucial in managing risk.

A new pre-commissioned controls and mechanical electrical board, installed and cutover from the existing board, helped to facilitate the cutover to the new arrangement and has addressed the critical issue of arc flash safety. Control of the Main Switchroom can be safely managed from outside the room which eliminates the life safety risk of switching in close proximity to circuit breakers with a rating of 3200Amps.

“HQ North is a prominent asset in our portfolio, with this electrification project marking a significant milestone in our broader efforts to enhance the precinct’s already strong sustainability credentials in the years ahead.” says Chris Eske, National Facilities & Operations Manager at Cromwell Property Group.

“We have been pleased to have the A.G. Coombs Group involved, with the technical capability and commitment of the team evident in their approach to the works.”

It is expected the new electric chiller plant will contribute significantly to Cromwell Property Group’s net zero emissions goals, while reducing complexity and providing significant savings in plant maintenance.

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This article originally appeared in BE – Building Efficiency 2023-2024 magazine