Performance of Ground Energy Systems Installed in Foundations

The UK and the European Union have legally binding targets for reducing carbon dioxide emissions and for the increasing renewable energy generation. As about 25% to 33% of the UK's annual energy usage is expended on space heating, the provision of renewable heat energy is an area of critical importance if emissions and energy targets are to be achieved. Increased use of ground energy systems within foundations and other underground structures would be beneficial in both these respects, and will be eligible for financial support through the forthcoming government Renewable Heat Incentive. However, despite a recent increase in the use of ground energy systems, there remain key areas of uncertainty about their performance. This is especially important in the long term, where multiple installations will interact with each other and where unbalanced heating or cooling loads will lead to changes in the thermodynamic regime in the ground. This project aims to address some of the uncertainties surrounding ground energy systems installed in foundations by comprehensively instrumenting and monitoring two sites in contrasting ground conditions. This will allow the real response of the ground to known heating and cooling loads to be measured, and comparisons made with predictions based on analytical and numerical models. The use of contrasting geological regimes will allow investigation of the impact of groundwater on the performance of systems, something rarely considered and not well understood. The field monitoring will be accompanied by a programme of in situ and laboratory testing to assess differences in thermal behaviour at different scales and temperatures relevant to ground energy systems. The testing programme will address questions relating to degrees of uncertainty in determining key thermal properties and how this may compare with other uncertainties in the system design, such as heating/cooling loads. Numerical modelling, including back analysis of the in situ thermal response testing and operation of the ground energy systems, will allow assessment of the sensitivity of the systems to different input parameters. The modelling will also allow evaluation of the numerical and analytical techniques currently used for the design of ground energy systems and assessment of the importance of key factors (geological variation, groundwater, surface boundary conditions, geothermal gradient) not currently accounted for in existing methods. Taken together, the various strands to the project are expected to provide an important dataset which will add substantially to the understanding of the performance of ground energy systems. By addressing uncertainties surrounding design input parameters, geological conditions and design approaches, the project will also provide relevant lessons for direct application to the design and construction of ground energy systems installed in foundations, which it is expected will ultimately form part of improved guidance for industry.

The benefits of this research will be far reaching, providing greater understanding of the combined thermal behaviour of the ground and concrete in contact with it that will ultimately lead to guidance for designers and contractors within the civil engineering industry. It will facilitate greater uptake of closed loop energy foundations, bringing clean renewable energy to public and private buildings. The work will therefore contribute to the carbon dioxide reduction targets for the UK and the European Union. The project will be run by the University of Southampton in collaboration with a number of industrial partners who will provide practical input, function as a steering group and be amongst the initial beneficiaries of the research. The project partners are leading engineering practitioners who bring a range of complementary skills to ensure the research is relevant to industry and assist with knowledge transfer to reach the widest range of potential beneficiaries. The partners, of whom full details are provided in the impact plan, are: i) Mott MacDonald, who will provide guidance from the perspective of an Engineering Designer, ii) Cementation Skanska, who will provide access to sites and practical assistance. They have also recently worked on the instrumentation of an energy pile in south London, iii) Golder Associates, who will provide guidance from a design perspective. In addition, WJ Groundwater will assist with the installation of instrumentation and in situ testing and will provide reduced rate drilling, installation costs and thermal response testing. Provision of research findings to beneficiaries will take place throughout the project. Dissemination to the project partners will occur rapidly and frequently through quarterly meetings of the steering group and via the University web based teaching tool Blackboard . This means that results from the research can be passed on to industrial practitioners as they become available. Towards the end of the project, the results will be published in quality journals (such as Proceedings of the ICE, Geotechnique, Proceedings of the ASCE, Canadian Geotechnical Journal) to make them available to the wider civil engineering community. Shorter articles for publications such as New Civil Engineer and Ground Engineering, which have a very large readership, will also be produced. Presentation at prestigious European and International conferences will allow dissemination to a wider audience. Ultimately the results of the research are expected to be incorporated into industry standard guidance and design documents that will facilitate safe and efficient uptake of ground energy systems throughout the UK and beyond. Using educational establishments (schools and colleges) to provide study sites also offers a unique opportunity to engage teachers and pupils with the project and with the topics of both renewable energy and the role of civil engineers in providing for a sustainable future.