Geothermal Energy Using Ground Source Heat Pumps

Abstract

Geothermal energy can mean many things to different people. A common view of this energy is that which is found in seismic regions where hot water and steam rise to the ground surface and can be harnessed for everyday use. Where this energy does not occur, boreholes can be extended downwards to obtain water at increased temperatures for use in a range of heating applications. If the conditions are appropriate, it is also possible to drill boreholes to several kilometres below the surface to extract water hot enough to produce electricity using turbines at the surface. However, there is another form of geothermal energy which makes use of the ground at normal temperatures within a few tens of metres of the surface as a heat source and sink to heat and cool buildings. The key element of this technology is the ground source heat pump or GSHP. In winter, the GSHP extracts heat from water circulating in ground loops and delivers it to a building. In summer, the reverse happens with the GSHP extracting excess heat from the building and dumping it to the ground. While direct geothermal energy is extensively used in other countries, it is rarely encountered in Australia and New Zealand. It is highly likely, however, that for a range of reasons, this is going to change dramatically in the not too distant future. This paper presents an overview of the principles of the technology and the various factors which influence the capital and operating costs of these systems. Consideration will be given to common design methods and why it is important that more research and development needs to be directed at the performance of ground loop systems, particularly for conditions encountered locally.