The Dunedin City Council has spent $18,000 on a ''thermal energy map'' for the city that shows energy is there to be tapped.
The project, which is in its early stage, could enable larger commercial or government buildings to be heated by the city's wastewater.
Smart Alliances engineer Nick Meeten said the system worked by using a heat exchanger that took heat from the street sewer.
''We all use water, and a good portion of that is warm or hot water from showers, laundry and dishes.
''All of that heated energy goes down the drain.''
The wastewater flowed through pipes under cities, and in Dunedin, even in the depths of winter, stayed at a temperature of about 15degC.
That was partly from the hot water, but also because pipes were buried in ground that stayed at a stable temperature.
The idea was picked up by the council when council water and waste group manager Laura McElhone attended a sustainable infrastructure conference last year in Melbourne, at which Mr Meeten presented information.
Dr McElhone said the thermal energy map showed areas with a sufficient amount of energy were not far from the University of Otago and Dunedin Hospital.
Cr Aaron Hawkins said that provided opportunities for Dunedin.
''I think it's a really exciting opportunity, and that's not something you get to say about your wastewater network all that often.''
Cr Hawkins said wastewater was a renewable fuel source, as well as a local one which could be important if energy from elsewhere was not available.
The council and the University of Otago had set ambitious targets in terms of renewable energy and low-carbon alternatives, and the idea fitted with that, Cr Hawkins said.
''Now is the perfect time for major institutions in the city to be working together to get the best 21st-century infrastructure outcome for Dunedin.''
Mr Meeten said in the same way a heat pump took heat from the atmosphere, the technology took heat from wastewater, which was a much better conductor of heat.
It was cheaper to locate a heat exchanger near the pipe, which meant it was better to install the systems during new project builds, rather than retrofitting.
That could make the project a good fit for the university and hospital, both of which are in a building phase.
Mr Meeten said apart from efficiently using energy in the ground, the technology was one way of moving away from burning fossil fuels.
''We have to change.''
He said there were up to 700 established systems around the world, and the technology was widespread in Europe and Canada.
There were five examples in Australia, and five developed recently in Scotland, which had a target of installing 750.
Dr McElhone said the council got Smart Alliances to map the heat potential in Dunedin to discover if wastewater energy might be useful for the council in its own large buildings, or to enable discussions with other large power users in the city.
''They're saying through the CBD there is sufficient energy to look at the next stage of feasibility.''
It was uncertain what the council's role would be at such an early stage, but it could be from facilitating projects to selling the energy to ''anything in between''.
''It's very early days, but it's very cutting edge in terms of what's out there.''
Dr McElhone said if the council did start a feasibility study, there might be funding available from the Energy Efficiency and Conservation Authority.
Comments
Harness 15 degrees to heat what? Defrost footpaths maybe? Unless you wear a coat in your office or home all day then 15 degrees is too cold. Just a stupid Greens pipe dream wasting ratepayers money.
DCC, the hospital and University have a more pressing, real world problem around energy. That is the fate of the central boiler complex with the imminent demise of Cadbury. Just which user is going to replace Cadbury for all the steam / heat being generated? Or does this close as being uneconomic.
Anyone at DCC spending time on this issue or just wasting tens of thousands on Green pipe dreams?
15 degrees is more than enough to create usable room temperature conditions in buildings
The proposal here is similar to that used in ground-sourced heating systems.
The ground at a shallow depth stays at a constant temperature of about 12 degrees year round. The technology, like heat pumps, takes this energy and converts it into much higher air temperatures (this is also what a normal heat pump does).
15 degrees an be converted into much higher temperatures for heating purposes. The technology is not new and the concept is widely adopted in many homes now.
I believe all the heating at the Dunedin Airport is from a ground-sourced heat exchange system from an underground network of pipes across land owned by the airport where the ground temperature is constant at about 12-13 degrees all year round (yes, in spite of frosts etc. on the grounds surface).