A district energy scheme has just been turned on at Ngāi Tahu’s new development in central Christchurch. WILL HARVIE explains the engineering of energy efficiency.
It was supposed to a “world-leading” response to the earthquakes and demolitions in Christchurch.
It would be a “district energy scheme” that could link up to 1000 buildings in the central business district to an efficient electricity generation and heating and cooling system that burned renewable waste materials and biomass. It would make rebuilt Christchurch better after the trauma of the earthquakes.
It didn’t happen how the dreamers hoped. Instead most property developers went their own way and installed heating and cooling plants that serviced only their own new buildings.
Until last month, there hasn’t been an actual district energy scheme – one that crosses streets – and links electricity generation and heating and cooling systems in different buildings and developments. Now such a scheme has been switched on.
* Ngai Tahu’s new $85m Christchurch office complex will strengthen city’s mana
* Editorial: A district energy scheme would have been a green dream
* Grand scheme to heat Christchurch city a ‘total failure’
* Canterbury District Health Board pulls out of energy centre
It’s mostly services Ngāi Tahu’s new $85 million Pita Te Hori Centre on land once used by the military’s King Edward Barracks and later the police’s Christchurch central station, which was imploded in 2015.
But it also crosses the street to the Christchurch City Council’s headquarters and even links to a landfill about 9 kilometres away as a gull flies.
If it can be profitably emulated, the Christchurch District Energy Scheme points to future energy efficiency in Christchurch and across New Zealand, says general manager Roger Sutton.
It’s an innovative scheme and probably unique in the world, says Sutton, the former chief executive of the Canterbury Earthquake Recovery Authority.
He’s an engineer who rose to be chief executive of Orion Energy, the electricity distribution company in central Canterbury, before heading up the recovery authority and then losing the job to scandal.
He resurfaced recently and his new job is to grow the Christchurch scheme within the central city.
The Pita Te Hori Centre – name after an important Ngāi Tahu ancestor – includes two five-storey office buildings leased to engineering, accounting and insurance firms, the ministries of health and education and a car park building. Ngāi Tahu isn’t a tenant.
The energy scheme is mostly sited on the ground floor of the car park building and has three three main elements.
The first taps into a fresh water aquifer, known the Wainoni Gravels, about 130 metres underground. Aquifers are perhaps better known for provided drinking water in New Zealand, but in this case 100 per cent of the water is returned underground after use.
The water temperature is always 14 degrees Celsius, which pleases engineers because they can rely on this constant to design a system that efficiently extracts energy from the water using heat exchangers.
The technology is like that used in domestic heat pumps. They gather air from outside a building, extract the available energy using heat exchange technology and then heat or cool the inside of a home.
The Christchurch scheme substitutes aquifer water for air – with the added advantage that the water temperature is constant.
The extracted heat is circulated through the two Ngāi Tahu buildings as heating and cooling, and joins solar panels on the roof and LED lighting to make the development energy efficient.
The second element of the scheme involves a pipeline that moves methane gas from the Burwood landfill to the Christchurch City Council headquarters, which are across the street from the Pita Te Hori Centre.
Methane is a greenhouse gas that some landfills produce. Capturing the gas for burning earned city council carbon credits used to partially fund energy efficiency schemes in the city.
The methane is burned in an engine in council’s plant room and the energy provides electricity, heating and cooling to the council building, as well as cooling to the Christchurch Art Gallery some blocks away. This “tri-generation” system was installed when council headquarters were renovated some years before the earthquakes.
However, it produces surplus heat and a new hot water pipeline will be built later this year that will tie council’s methane-burning engine to the Christchurch scheme across the street.
The third element of the scheme is a 15,000 litre heavily insulated water tank tucked into the Ngāi Tahu’s plant room. It’s sort of a water battery that stores heat.
That energy can be used to heat Ngāi Tahu’s buildings, especially at high-cost peak times, when as Sutton points out, electricity is often generated with non-renewable energy.
The thermal store can supply heat for about 90 minutes, so it’s a short-term solution to high energy costs.
By themselves, the three elements amount to a $2m investment that will cut energy in Ngāi Tahu’s buildings by about 50 per cent, Sutton said.
That’s good but the value of a district energy scheme leaps when more streets are crossed and more buildings added to the system, says Fraser Jonker, the chief executive of Pioneer Energy, one of the joint venture partners that created the Christchurch scheme.
The plan is to create energy efficient hubs around the central city and then link them by pipelines as opportunities arise.
Done right, the network will be more energy efficient than standalone systems.
Pioneer already owns district energy schemes in Timaru and Dunedin but reached out to French energy conglomerate Engie for advice and capital for the new one in Christchurch.
Engie, which had 2016 revenues of more than €66 billion (NZ$107b), operates about 300 schemes around the world, including some in heritage Paris and wants more.
“The bigger they are, the more efficient they are,” said Didier Holleaux, an Engie vice president who visited Christchurch last month.
Engie and Pioneer own the Christchurch energy scheme and Ngai Tahu pays fees for heating and cooling services. That leaves Sutton free to expand the scheme and collect revenues for the scheme owners.
Renewable electricity generation varies
New Zealand’s electricity generation changes through the year as environmental conditions change, the Electricity Authority says.
In January, hydro generation accounted for about 60 per cent of all generation. This dropped to about 50 per cent of total generation in June as water volumes in South Island hydro lakes fell.
Wind generation accounted for about 6 per cent of total generation in January. This reduced to about 2 per cent in early June. Since 2014, wind generation has fluctuated between 2 per cent and about 7 per cent of total generation.
Almost all wind generation occurs on the North Island.
Solar generation accounts for less than 0.5 per cent of total generation across New Zealand but the authority cannot provide information about the variability of solar output.
It says, however, that there was almost 52 megawatts of solar capacity installed across New Zealand at the end of July 2017, up from 25 megawatts in July 2016.
Geothermal generation is more constant. It’s worth about 20 per cent of total generation throughout the year.