Introduction to Geothermal Systems
This page is dedicated to introduction of geothermal heating and cooling technology and other sustainable energy solutions. Please click on each topic to get more information.

Geothermal systems efficiently heat and cool buildings using sustainable geothermal energy accessed via Ground Heat Exchangers (GHEs). In closed loop systems, GHEs comprise pipes embedded in specifically drilled boreholes or trenches or even built into foundations, all within a few tens of metres from the surface. The geothermal systems are just starting to be generally known in Australia with relatively few, but highly varying and diverse installations to date offering a potentially economically viable and environmentally friendly method for heating and cooling of buildings.
However, they require excavation or drilling to bury the GHEs which lead to higher capital costs for installation in comparison with conventional systems. The design of GHEs in Australia is mostly achieved with simple rules of thumb, and simple software that has been developed but not validated for the GHE design.
The high capital cost of GHE installation is one of the main causes preventing wide adoption of direct geothermal systems in Australia. It is therefore imperative that GHEs should be designed as efficiently as possible to minimize the extent and cost of GHE installation.

At GeoFlow Australia, we are using the current design methods together with the design methodology achieved by our head of design team, Dr Amir Kivi through 4 years of research at The University of Melbourne. This is to ensure that the GHE is sized to the needs of the house and to avid under-sizing and over-sizing the heating and cooling system.

 

Introduction to Geothermal Systems
Geothermal systems efficiently heat and cool buildings using sustainable geothermal energy accessed via Ground Heat Exchangers (GHEs). In closed loop systems, GHEs comprise pipes embedded in specifically drilled boreholes or trenches or even built into foundations, all within a few tens of metres from the surface. The geothermal systems are just starting to be generally known in Australia with relatively few, but highly varying and diverse installations to date offering a potentially economically viable and environmentally friendly method for heating and cooling of buildings.
However, they require excavation or drilling to bury the GHEs which lead to higher capital costs for installation in comparison with conventional systems. The design of GHEs in Australia is mostly achieved with simple rules of thumb, and simple software that has been developed but not validated for the GHE design.
The high capital cost of GHE installation is one of the main causes preventing wide adoption of direct geothermal systems in Australia. It is therefore imperative that GHEs should be designed as efficiently as possible to minimize the extent and cost of GHE installation.

At GeoFlow Australia, we are using the current design methods together with the design methodology achieved by our head of design team, Dr Amir Kivi through 4 years of research at The University of Melbourne. This is to ensure that the GHE is sized to the needs of the house and to avid under-sizing and over-sizing the heating and cooling system.

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Geothermal components

 

Principal Elements of a Geothermal System
• The heating and cooling distribution system inside the building,
• The Ground Source Heat Pump (GSHP) which causes heat to flow “uphill” from lower temperature to higher temperature,
• The Ground Heat Exchanger (GHE) pipes buried within a few tens of metres of surface as a heat source in winter and heat sink in summer.
A heat transfer fluid (typically water) is circulated through GHE pipes and exchanges heat with the surrounding ground. If the fluid is cooler than the ground, the ground will heat it and if the fluid is hotter than the ground, it will be cooled. GSHPs efficiently upgrade the heat extraction/rejection process. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor heat delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger.

 
 

Why Geothermal?
The key to the geothermal system is that for each kilowatt of electrical energy put into a geothermal system, depending on several parameters, about 4 to 5 kilowatts of energy is developed for the purposes of heating and cooling. This means that geothermal systems could reduce electricity demand for heating and cooling by 75%. Furthermore, as much of the electrical power in Victoria is generated with brown coal, replacing 75% of the energy used with a clean and free renewable energy source, these systems will have the potential to significantly cut Australia’s carbon footprint.

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Global Growth Rate of Geothermal System Installation
It is estimated that there are over 3 million direct geothermal systems installed around the world, with the total installed capacity approximately doubling every 5 years since 2000 (Lund et al., 2010). This includes the capacity and annual utilization of all forms of geothermal energy for heating and cooling applications.

 
 

Types of GHE Configuration
Different GHE configurations are classified as open loop and closed loop.
Closed loop GHEs comprise pipes placed in the ground or water through which a fluid circulates and the heat exchange occurs by conduction through the walls of the pipes. Therefore, the fluid remains sealed in the pipes and does not come into contact with the energy storage medium. There are several advantages to this system. One of the main advantages is that there is no problem of contamination either from the loop water entering the ground, or perhaps more critically, from the ground water contaminating the workings of the pumps.
Where there is a confined surface area or minimum disruption of the landscape is desired, GHEs in form of vertical boreholes (of varying diameter) comprising one or more “U-loops” of high density polyethylene (HDPE) pipe are installed in a borehole backfilled with cement/bentonite grout.
Horizontal trenches are usually the most cost-effective when adequate area is available around the building and trenches are easy to dig. Different configurations of horizontal GHE can be constructed. The horizontal GHE has become increasingly popular due to its low cost and ease of installation. For instance in Canada, about 55% of direct geothermal installations use horizontal GHEs (CGC, 2011). Nevertheless a horizontal GHE requires a large area of ground to lay the pipe network. This problem can be alleviated to some extent by employing a slinky loop arrangement of the pipes. Slinky arrangements are coils of overlapping piping, which are spread out and laid either horizontally or vertically. This GHE’s ability to focus the area of heat transfer into small volume reduces the length of the trenches by 20-30% of those for single pipe configuration (Wu et al., 2010). The slinky coils can have different lengths per unit length of trench depending on the pitch spacing of successive coils. The performance of slinky coils is similar to straight pipes with an equivalent total length (IGSHPA 2011).
In an urban environment, the ground immediately below a city can be used as a low grade energy storage reservoir. Geotechnical structures such as piles, tunnels, sewers, retaining walls and ground slabs can be regarded as thermo-active structures by simply embedding GHE pipes in them.
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