Biogas fuels civic building

By - , Build 122

A successful renovation has turned the old New Zealand Post building into Christchurch City Council’s new award-winning civic building. The energy-efficient building uses a tri-generation system powered from biogas – a world first.

The old New Zealand Post building has been transformed into a new, energy-efficient Christchurch Civic Building.
Christchurch civic building has been awarded six green stars and won an EECA award for its energy efficiency.

When Christchurch City Council and joint venture partner Ngāi Tahu Property undertook to transform the old New Zealand Post building into a new civic headquarters, they aimed to create an ‘exemplary net zero-carbon building’. This reflected the council’s vision for a sustainable energy future, contained in its 10-year regional energy strategy, and promised significant cost savings for ratepayers. Redevelopment was chosen over a new build – renovating avoided using 18.25 GWh of energy and emitting 6,440 tonnes of CO₂.

Athfield Architects were commissioned and Powell Fenwick Consultants provided the mechanical and electrical design work. When the building achieved its co six green stars, it attained 21.9 out of a possible 25 for its energy use. The New Zealand Green Building Council also awarded four ‘innovation’ points for energy-related design features.

The $113 million redevelopment was completed in August 2010, making it the first six green star building to be in use in New Zealand.

Energy-efficient design features

The building uses passive design elements and sensor technology to optimise occupants’ comfort and reduce energy consumption.

The northern double-skin façade acts as a thermal solar buffering zone. A monitoring system detects when CO₂ has reached a certain level, and fresh air is automatically introduced through floor vents. The full range of energy-efficient features includes:

  • double-skin façade
  • automatic louvres to prevent solar gains
  • lighting system that adjusts output according to natural light levels and room occupancy
  • air distribution system using a raised floor and vents
  • LED lamps for outdoor lighting
  • lifts with a regenerative breaking system
  • escalators controlled by motion sensors
  • low-flow bathroom fittings
  • rainwater harvesting (expected to provide 1 million litres per year) for toilets, landscape irrigation and a water feature
  • solar collectors on the roof for water heating
  • bicycle racks for 16% of staff (green star benchmark is 10%).

Future-proofing features included

The building design has been future-proofed by including extra take-offs for chilled water and an electrical connection to export electricity and chilled water to the adjacent art gallery site during non-business hours. This separate project is planned for implementation in 2011 and will make the civic building a net zero-carbon building as well as a net exporter of renewable energy.

The old New Zealand Post building has been transformed into a new, energy-efficient Christchurch Civic Building.

Tri-generation a world first

An outstanding feature of the new building is a tri-generation plant – an advanced, highly efficient form of co-generation. This means the building generates its own electricity from biogas. This is the first tri-generation system in New Zealand and the first in the world to run on biogas.

The tri-generation system provides all the building’s electricity, heating and cooling needs. Biogas is piped 18 km from the council’s landfill and wastewater treatment plant. Waste heat from this process is used to heat and cool the building, representing energy savings worth $0.7 million per year.

The plant has the capacity to generate up to 475 kW of electricity, 712 kW of hot water and up to 482 kW of chilled water for cooling, simultaneously.

Local design improves on original

Opting for a New Zealand-first installation provided challenges. The original project was based on an American turnkey solution. However, the design team had to overcome an unexpected barrier when the manufacturer couldn’t supply the equipment.

Table 1: Christchurch civic building annual estimated energy and CO₂ savings.
  Displaced fossil fuels (MWh/year)   CO₂ reduction (tonnes/year)   Peak electricity load reduction (kW)
  LPG Electricity LPG Electricity  
Building energy systems and features 1,100 3,100 237 1,860 475
Less energy for biogas compression*   0*   0* -25
Total   4,200   2,097 450

*Electricity used is generated from biogas at the Christchurch wastewater treatment plant, not from fossil fuel combustion.

After reassessing the options, the team adopted a locally designed configuration of the plant. The redesigned plant was based on a reciprocating engine generator (rather than the microturbines of the original), a custom-built heat recovery unit, an absorption chiller and locally sourced auxiliary and control systems. This resulted in an improvement on the American model. The plant appears to have better local serviceability, operating flexibility and tolerance to impurities in the biogas.

Innovation recognised with award wins

In November, the council’s energy-efficient vision was recognised when it won the public sector category of the 2010 Energy Efficiency and Conservation Authority awards with Ngāi Tahu Property for its new civic building and the renewable energy category for its city-wide use of bioenergy.

The council and Powell Fenwick were also highly commended in the innovation section for its tri-generation plant. The judges said the project ‘showcased the best in sustainable buildings’.

Christchurch civic building has been awarded six green stars and won an EECA award for its energy efficiency.

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The old New Zealand Post building has been transformed into a new, energy-efficient Christchurch Civic Building.
Christchurch civic building has been awarded six green stars and won an EECA award for its energy efficiency.

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