Going with the flow

Geothermal energy was used by the Romans for bathing and heating; and there is also evidence to suggest cooks in pre-historic France relied on heat extracted from the earth to heat water; so it’s safe to say geothermal energy is not a new or complex concept.

However, as the world searches for sources of renewable energy to solve one of our century’s greatest challenges, Professor Ian Johnston, from the University of Melbourne’s School of Engineering is focusing his energy on this “totally renewable, totally sustainable 24/7 energy source.”

There are two basic forms of geothermal energy in Australia. The first is an indirect form which uses heat extracted from hot rocks that lie deep below the surface to generate electricity. It is predicted however, that commercialisation of this type of technology is at least a decade away.

The second form – which is the focus of Professor Johnston and his team – is a direct form of geothermal energy. It uses the ground within a few tens of metres below the surface as a heat source in winter and a sink in summer.

It is this direct form of geothermal energy that is ready to go. In fact, Professor Johnston says the amount of geothermal energy currently used around the world for direct heating and cooling using ground source heat pumps is equivalent to about 16 Loy Yang power stations.

“While direct-use geothermal energy may not produce electricity, its ability to replace current carbon emitting forms of heating and cooling is huge, and this would have a huge impact,” Professor Johnston says.

The direct-use geothermal system works by circulating fluid – water or refrigerant – down into pipes that are installed within building foundations or into purpose-drilled boreholes, and then back to the surface again.

In winter, heat contained in the circulating fluid is extracted by a heat pump, and used to heat the building. In summer, the system is reversed, with heat taken out of the building and transferred to the fluid which rejects it underground.

Professor Johnston says – depending on certain factors – around 100m to 150m of buried small diameter pipes can continually provide most heating and cooling requirements in the average family home, and that larger buildings can be accommodated with greater lengths of pipe incorporated into their generally larger and deeper foundations.

“The system is more reliable than wind and solar as it is able to operate continuously,” he says.

“This system is also relatively maintenance free and the cost of instalment is modest and recovered rapidly with the savings you get. While it costs about $10,000 to install a typical residential system; you would make your money back within about 10 years, after that you could considerably reduce your energy bills.”

Large-scale systems for commercial buildings could have even shorter pay back periods.

While heating and cooling may not be perceived as a huge contributor to climate change, recent figures show that 26 per cent of carbon emissions come from buildings; and that half of a building’s emissions result from heating and cooling systems.

“While this type of heating and cooling system requires electricity for circulation and heat pumps, it is minimal, so for every kW of electricity used, you get about 4kW of heating energy out,” Professor Johnston says.

While the benefits of this system are numerous and the technology is ready to go, one obstacle remains to making it a widespread and commercially viable system in Australia.

That remaining stumbling block is knowledge of exactly how much pipe is required to adequately and economically heat and cool a house or business according to research team member Dr Guillermo Narsilio from the Department of Civil and Environmental Engineering

And this is exactly the knowledge that Dr Narsilio and Professor Johnston hope to gain from their current research project. Along with PhD student Stuart Colls, who is being partly supported by consulting engineers Golder Associates Pty Ltd, and working in collaboration with Direct Energy Ltd – who will provide detailed advice and heat pump equipment – and Geotechnical Engineering Pty Ltd – who will assist the team with drilling – the team will conduct field trials on campus.

Data obtained from these trials will enable the development of design guidelines such as taking into consideration ground temperature, the type of soil or rock and size of a property, which will determine how much piping will be necessary and the best means of installation.