Performance of Borehole Ground Heat Exchangers Under Thermal Loads from a School Building: Full-scale Experiment in Melbourne, Australia

Abstract

The ground at shallow depths can be used as a source of sustainable thermal energy for heating and cooling buildings. Utilisation of this energy reduces the amount of fossil fuel required to maintain comfortable temperatures inside buildings and can significantly reduce the operating costs of heating and air-conditioning. A Ground Source Heat Pump (GSHP) system is a technology that extracts geothermal energy from shallow depths and transfers it to buildings. Currently, installation costs of these systems are relatively high and this can prevent potential users from investing in these systems. Ground heat exchangers (GHEs) are the least researched and the most expensive elements of GSHP systems. Hence, further research into the performance of GHEs is needed to develop a sound basis for their optimum design and, ultimately, to reduce lengths of GHEs and decrease installation costs of the GSHP systems. A new two storey school building of about 1500m2 floor area in Melbourne, Australia was fitted with a GSHP system as part of a research and demonstration project funded by the Department of State Development, Business and Innovation (DSDBI). Twenty eight 50-metre deep borehole GHEs were installed to provide heating and cooling energy for the school and the building is being used as a full-scale experiment to study the behaviour of GHEs under real-life thermal loads. Nine of the GHEs were extensively instrumented to monitor their thermal performance. Also, eight additional monitoring boreholes were installed to study thermal influence of GHEs on the adjacent ground. The experiment will allow a better understanding of thermal processes in the ground when thermal energy is injected and extracted to/from it. This paper presents some of the initial data obtained from this unique project.