EPSRC-FAPESP Efficient ground energy systems for deployment in diaphragm walls under challenging application scenarios

This project has been developed under the EPSRC lead agency agreement scheme with FAPESP, Brazil, that allows joint international working. The project is therefore to be delivered by an integrated team in the UK and Brazil ; working across the fields of geotechnical engineering, thermal analysis and building services engineering bringing together a team of Geotechnical and Mechanical Engineers.

The project tackles heating and cooling of buildings, which is a key priority for meeting NetZero targets. Almost half of global energy use is related to heating (one quarter of UK emissions). Cooling is a minor, but growing emissions source in the UK, but globally energy consumption for cooling has more than tripled since 1990, and will continue to increase with climate change. In Brazil, cooling public and private buildings is responsible for half of national electricity demand (predicted 40% increase by 2035). Thermal energy solutions that can deliver against these cooling and heating demands urgently need to be developed. In the UK, heat pump deployment is not progressing as fast as is required, while in Brazil, there is an absence of demonstrator projects showing local feasibility. Heat pumps are suited to both heating and cooling, with ground source heat pumps (GSHPs) offering high efficiencies. However, innovation is required to reduce capital costs.

Inclusion of heat transfer pipes within sub-structures, so called energy geostructures, is one way to reduce costs of GSHP systems. This project aims to tackle the problem of developing embedded retaining walls for application in thermal energy. Embedded retaining walls, e.g. constructed to support underground car-parks, are themselves costly structures that can have very long lifetimes. Currently their use is restricted to retaining the ground, but they could be built to have dual purpose by incorporating them in a GSHP system. This would seem like an obvious thing to do but it adds additional complexity in design and construction. The benefits and potential for optimisation, especially in difficult ground conditions, are unproven. Thus, research is required to convince industry and developers to adopt these systems. This project will equip them with the appropriate design tools and knowledge to incorporate highly efficient and optimised energy retaining walls into GSHP systems.

We will construct a controlled field study site at the University of Sau Paulo (USP) in Brazil that will include an instrumented retaining wall system with different pipework geometries to allow a wide variety of wall operation modes to be studied. This will create an important data set specific to the local South American climate and ground conditions. Initial design of the system will be aided by numerical simulation (University of Leeds) which will also serve as a benchmark to judge subsequent simulation and analytical model development. Scaled physical models of the USP test site and wall arrangements will be fabricated at the University of Dundee and tested on a geotechnical centrifuge. These physical models will be validated against the field data collected. Centrifuge testing will be used to vary different parameters that cannot be easily controlled on site and test deeper walls and ground conditions similar to brownfield land development in the UK. The University of Leeds will then use the data and insights from the field and physical model studies to develop thermal analytical tools for design of these structures. This will result in fast run transient solutions for energy walls that can work in a variety of ground conditions and be integrated with existing building energy modelling software. Development of these tools will then be available for practical design of more efficient embedded retaining wall GSHP systems and remove barriers to adoption.