Christchurch Rebuild: Harnessing water power

Justin Hill, Manager of Beca's Building Services team. Photo / Dean Carruthers

Engineering Consultancy Beca is working with major developers in the Christchurch rebuild to deploy their innovative artesian water systems as an efficient and renewable energy source for cooling and heating.

"Christchurch naturally has a water temperature of around 12C, enough to cool a building," says Justin Hill, Manager of Beca's Building Services team.

The design enables the system to use the natural temperature of the artesian water without the need for any mechanical cooling. "This makes it really energy efficient because the only energy being used is that from the pumps, yet you're cooling this entire building."

For further cooling, and producing chilled water, chillers can be used in a system by Beca, which completely reuses the heat by-product.

"At the same time that these chillers are producing cold water, they have to take the heated energy out of that water and they have to get rid of it somehow," say Hill. "We put the heat energy back into the artesian water and elevate the temperature of that water."

"As we developed this further we realised that we could direct the heated energy back into the building. That's what makes it really energy efficient because it's literally just moving that energy around the building and directing the heat energy and cooling energy wherever it's required in the building. "

Beca's innovation enabled the technology to be twice as efficient, generating an even larger payback. "A standard heating system using gas boilers for example would operate at about 93 per cent efficiency, these chillers that we are using produce heated water at an efficiency of about 600 per cent. You put 1 kilowatt in and you get 6 kilowatts out and at the same time we can get 7 kilowatts of cooling energy out."

The first system was designed for Christchurch International Airport (see above) and its new integrated terminal layout, which opened last year following a major overhaul. "We started back in 2005 and culminated with the opening of stage one in 2011, just following the earthquakes," said Hill. He said the work at the airport was being put forward to the Association of Consulting Engineers of New Zealand for an engineering excellence award.

The earthquake rebuild has revitalised interest in artesian systems and their use is being seen in a number of developments around the city. The 23-building Arts Centre complex will use the system, as will the $140 million The Terrace development being built by Antony Gough. It is said to have been one of the features that enabled Gough to secure Westpac Bank as a key tenant.

Christchurch Council is actively looking to promote the use of artesian systems and similar technologies. The Christchurch Agency for Energy, a charitable trust set up by the council in 2010 to promote energy efficiency, put forward a $1.8m fund for the council to administer. The fund is available for private sector developments of at least 1000sqm that use renewable sources of energy - those that qualify can receive up to $300,000 towards the plant costs.

The scheme is designed to make it more affordable for major developments to use renewable energy such as artesian water systems. The technology tends to be a more expensive investment up front, but in the medium to longer term should provide significant operational savings and be better for the environment.

How it works

Artesian water is sourced through wells tapped into the natural aquifers that are plentiful in Christchurch. The aquifers have an internal pressure built up between layers of rock.

In Christchurch they can be bored as deep as 100m in the ground and produce a fountain above ground in excess of 10m.

When a well is dug the pressurised water rises up naturally without the need for a pump. To keep this system running in perpetuity, the artesian system returns the water back into the aquifer so it runs in a closed cycle, which is a completely non-consumptive use of the resource.