The benefits of direct geothermal energy

Features, Research, Slideshow — By Jennifer Thomas on July 12, 2011 5:35 pm

Energy use in buildings accounts for about one quarter of Australia’s greenhouse emissions, and over half of this is for heating and cooling. The introduction of direct geothermal heating and cooling to Australia, even on a moderate scale, would have a significant impact on power requirements. There would be enormous economic and environmental benefits. As virtually every building in Australia requires some form of heating or cooling, direct geothermal energy could influence every Australian and their carbon footprint.

Professor Ian Johnston, Dr Guillermo Narsilio, Dr Lu Aye and PhD students, Asal Bidarmaghz, Stuart Colls and Tshewang Lhendup, from the Department of Infrastructure Engineering’s Geotechnical Research Group, are conducting a detailed direct geothermal energy field trial, heating and cooling a site on location at the Parkville campus of the University of Melbourne.

There are two basic forms of geothermal energy – direct and indirect. Indirect uses heat extracted from hot rocks that lie deep below the surface to generate electricity. It is likely that commercialisation of this type of technology is at least a decade away. Professor Johnston and his team are interested in the direct form of geothermal energy, which uses the ground within a few tens of metres below the surface to extract heat in winter for heating and to sink heat in summer for cooling.

“Although using direct geothermal energy does not generate electricity, its ability to replace carbon emitting forms of heating and cooling has the potential to have a huge impact on reducing our carbon footprint,” says Professor Johnston.

The system works by circulating fluid, water or refrigerant, down 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, depositing it underground.

While geothermal energy, unlike some other renewables, is constantly available at any time of day, its use has been limited in Australia, to date. The technology is widely used in other parts of the world, however. Professor Johnston says that direct geothermal energy is more reliable than wind and solar as it is able to operate continuously. In addition, the system is relatively maintenance free and the cost of instalment can be recovered through reduced energy bills.

“For each kilowatt of electrical energy put into a direct geothermal system, about 4 kilowatts of energy is developed for the purposes of heating and cooling, reducing the energy cost by 75%,” Professor Johnston says.

While the benefits of this system are numerous and the technology is ready to go, there are several problems the team hope to address that are stopping the current technology from being widespread and commercially viable in Australia. Research is being conducted into how much pipe is required to adequately and economically heat and cool residential and commercial premises. Data obtained from the field 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. In addition, although there have been a large number of direct geothermal installations worldwide, many of these have been driven by the heating, ventilation and air conditioning industry. There has been little technical input from geotechnical engineers into their design. This has led to numerous, very approximate guidelines of what should be installed in the ground to provide the energy required.

“With better technical information, the systems developed could be more cost-effective and competitive,” says Professor Johnston.

The testing and monitoring facility at Parkville campus will provide an extensive range of information for the development of design and construction guidelines specifically for direct geothermal heating and cooling systems on campus and in the Melbourne region. This is the first of a number of similar installations being developed at different locations and for different ground conditions in Victoria.

“We aim to demonstrate that direct geothermal energy is a reliable, cost-effective and renewable form of energy for a wide range of domestic, commercial and industrial applications where heating and cooling is required”, Professor Johnston says.

Tags: infrastructure engineering, MSE, research