What is direct-use geothermal?
Direct-use geothermal is the use of naturally-occurring heated substances located in the ground, typically via an open cycle system, with the ground heat exchange occurring at the earth’s surface. Direct use of geothermal normally requires accessing heated groundwater that is naturally circulating through sedimentary strata or fractures rock. Hydrothermal systems with fluid less than 150°Celsius are best suited to direct-use applications.
How is geothermal heat extracted for direct-use?
Heated water or wet steam from a hydrothermal system is extracted through a bore and passed through pipes or coils at the surface to provide energy for a particular process. The cooled fluid is then often recirculated back into the aquifer through a second bore to maintain a sustainable system.Article continues below…
How can direct-use geothermal heat be used?
Direct-use geothermal heat can be used in agriculture for greenhouse heating or crop drying as well as in aquaculture and space heating. It can also be used for industrial processes such as concrete curing, milk pasteurisation, chemical extraction, refrigeration, drying organic materials (seaweed, grass etc), desalination, wool processing and pre-heating of water in coal-fired power stations. Direct-use geothermal also has residential applications such via a ground-source heat pump (GSHP).
What is a ground-source heat pump?
GSHPs typically circulate fluid through a shallow closed-loop piping system in the earth or a water body to use the relatively constant temperature of the rocks or water as a heat source or a heat sink.
High temperatures are not needed, and these systems can be applied almost anywhere. In winter, cold liquid pumped into the ground absorbs heat from the surrounding rocks, and the warmed liquid that is returned to the surface can be used to heat buildings.
Conversely, warm liquid pumped into the ground in summer will lose heat to the relatively cooler surrounding rocks, and can be used to cool buildings.
When the temperature contrast between the ground and air temperature is at a maximum, which usually occurs at the height of summer and winter, the ground source heat pumps run most efficiently and provide the greatest potential for cooling or heating.
Although ground source heat pumps are electric-powered, they are used only to move heat, not to produce heat. As a result, they are energy efficient and usually have coefficients of performance (a measure of energy efficiency) greater than three.
This means that for every unit of electrical energy consumed, three units of energy are delivered in the heating or cooling process.
Existing direct-use geothermal applications in Australia
Direct-use of geothermal energy in Australia currently includes building and district heating systems, spa developments, artesian baths and swimming pool heating.
GSHPs have been installed in several locations, including at Geoscience Australia’s office building in Canberra, the Integrated Energy Management Centre and the Antarctic Centre in Hobart, and the Hobart Aquatic Centre. Refer below for details of direct-use geothermal installations in Australia.
New South Wales
- Lithgow Hospital, Lithgow
- NPWS Tourist and Information Centre, Jindabyne
- Macquarie University, North Ryde
- Detention Centre, Dubbo
- Cowra Shire Council Offices, Cowra
- Wagga Wagga Civic Centre, Wagga Wagga
- Surry Hills Community Facility, Surry Hills
- Woolloomooloo Wharves, Woolloomooloo
- Victoria University of Technology, Werribee
- Paynesville Pool, Paynesville
- Station Pier, Port Melbourne
- Wangaratta High School, Wangaratta
- Monash University, Melbourne
- Bandiana ALTC, Bandiana
- East Melbourne Library
- Royal Adelaide Hospital, North Terrace
- Bureau of Meteorology, Kent Town
- Garden East, 320 Apartments, Adelaide
- Cooper Pedy Police Station, Cooper Pedy
- Mt Barker TAFE, Mt Barker
- ACTEW Corporation, Canberra
- Geoscience Australia, Canberra
- Duntroon Headquarters, Canberra
- Airport Caltex, Pialligo
- ANU Research Laboratory, Canberra
- Grand Chancellor Concert Hall, Hobart
- Queen Victoria Museum and Art Gallery, Launceston
- Southern Cross Homes Aged Care, Moonah
- Antarctic Centre, Hobart
- Westpac Call Centre, Launceston
- Hobart Aquatic Centre, Hobart
- University of Southern Queensland swimming pool, Toowoomba
- Logan Institute of TAFE, Logan
- Bureau of Meteorology, Darwin
- Challenge Stadium, Pool
Opportunities for direct-use geothermal in Australia
Australia has significant potential geothermal resources associated with buried high heat-producing granites, and lower temperature geothermal resources associated with naturally-circulating waters in aquifers deep in sedimentary basins. There are extensive areas where temperatures are estimated to reach at least 200°Celsius at around 5 kilometers depth.
The Great Artesian Basin in Australia’s north is one of the largest underground water reservoirs in the world. It has large, low-temperature hydrothermal systems, with aquifers containing groundwater that comes to the surface as warm as 98°Celsius.