Research project: Foundations as an energy source

Around 50% of the UK and EU energy consumption is taken up by space heating of buildings. This excludes air conditioning, the use of which is rapidly increasing. Yet a major opportunity to reduce the heating and cooling energy required by buildings lies just beneath our feet. The ground is a relatively constant temperature throughout the year. This means that it is cooler than the outside air temperature in summer and warmer that it in winter. Consequently this temperature difference can be exploited by using a ground source heat pump system to extract or inject heat into the ground.

All such systems require a heat exchanger to be constructed within the ground. A recent innovation is the use of building foundations and other underground structures in the function of heat exchangers as well as providing structural support to the overlying civil engineering structure. However, there is an absence of standard analysis methods for foundation heat exchangers.

Research Areas

Research at the University of Southampton is working to develop new analysis methods and guidance for design input parameters so that the energy efficiency of ground heat exchangers can be maximised.  Specific research topics include:

• Determining the thermal properties of soils and rocks. These are essential parameters for the analysis of foundation heat exchangers, and determining the amount of energy obtainable from the system.  A range of laboratory and in situ test methods are being investigated to allow for improved guidance for practice.
• The thermal properties of concrete used in foundations.  Short term heat storage as well as long term heat transfer through the concrete foundations is important for the behaviour of energy foundation systems, yet surprisingly little guidance is available selecting parameters.
• Predicting the temperature changes that occur within and around the foundation heat exchanger.  This is important for both determining energy output and preventing excessive temperature changes that may impact the structural function of the foundation. New analysis methods are being developed for foundation piles that are significantly less conservative that existing approaches.
• In situ characterisation of the thermal properties of pile heat exchangers by thermal response testing.  This is a well-established technique for more common types of heat exchanger, but best practice in testing and interpretation is still to be developed when applied to piles and other foundations.

Current research is proceeding by a combination of laboratory testing of materials, in situ monitoring of operational and test piles, and development of new analytical and numerical solutions.  For more information about this project please contact Dr Fleur Loveridge.

Impact

Early results from our work have been included in the ground breaking Ground Source Heat Pump Association Thermal Pile Standard , with further research updates presented at the Ground Heat Source Pump Association regular Technical Seminar series.

• The thermal behaviour of piles used as heat exchangers
• The importance of the concrete in thermal pile behaviour
• Selected journal and conference contributions related to this project are also included below.

Funding

This project is supported by the following awards:

• EPSRC project EP/H049010/1 "Performance of Ground Energy Systems Installed in Foundations"
• Royal Academy of Engineering Research Fellowship "New Thermal and Geotechnical Facility for Ground Heat Exchangers"