Shallow Geothermal Energy: An Emerging Technology

Shallow geothermal energy systems use the upper few metres of the ground below the surface to provide space heating and cooling efficiently. Well-designed systems render year-round coefficient of performance (COP) of about four or more. In closed-loop geothermal systems, high-density polyethylene (HDPE) or cross-linked polyethylene (PEX) pipes are embedded in trenches, boreholes or into geostructures (e.g. piles) to form ground heat exchangers (GHEs), whose function is to access this sustainable geothermal energy. A large proportion of electricity worldwide is generated from fossil fuels. Substituting commonly used electric heating and cooling systems with shallow geothermal ones could significantly decrease peak energy consumption and greenhouse gas emissions given their high COPs and high primary energy ratios. This chapter summarises the fundamental principles of the technology, the various factors that affect the thermal performance of different types of GHEs and their impacts on the capital and operating costs of geothermal systems. In addition, this chapter provides an overview of what the future might hold in terms of using geostructures with a dual purpose, as load-bearing-buried structures and as GHEs. Consideration is given to common design methods and an example is presented using a simplified design method. The chapter highlights the importance of directing additional efforts in research and development of the performance of ground loop systems.