Application of Geothermal Energy

BACKGROUND 

Energy foundations utilize the necessary structural elements of a foundation and combine them with a geothermal energy

 transfer mechanism. Piles, diaphragm walls, basement slabs, tunnel anchors, and tunnel linings are just some of the foundation elements that have been combined with geothermal elements (Brandl, 2006). Geothermal piles, also referred to as heat absorber or energy piles, are a type of energy foundation which utilize subsurface geothermal energy to heat or cool the building which it supports. There are many types of geothermal piles available. Driven steel and ductile cast iron, as well as pre-fabricated driven and bored cast-in-place reinforced concrete are the most common geothermal piles. The difference between typical piles and geothermal piles are the additional high-density polyethylene (HDPE) plastic pipes installed within the pile which circulates a heat transfer fluid. The fluid is then connected to a heat pump system installed within the building which is then used to heat or cool the building and for deicing of airport runway and road pavement.

Implementation of geothermal piles, like any structure, has both advantages and disadvantages. Reduction of both fossil fuels and material contribute to a sustainable product. When designed properly, the recycling effect from drawing and depositing heat in the soil subsurface also contribute to the sustainable function of the foundation system. The initial cost is too larger than conventional systems because of additional design and material costs for both the foundation and the heat pump system. However, annual savings have been shown to have a payback period of less than 10 years for most systems (Brandl, 2006).Use in areas where freeze-thaw cycles occur in soil should be avoided, as this can cause heave or settlement issues of the pile as well as possible damage to the heat transfer tubing. Geothermal piles include a more complex interaction between the soil and pile than conventional piles. A framework for understanding geothermal pile behavior is easily understood by considering or investigating the thermal loading, the mechanical loading, and the combined thermo-mechanical loading. The end conditions or restraint of the head and toe of the pile are shown to greatly affect the stresses and strains experienced within the pile. While advances are being made in analysis of the geothermal response, their performance under dynamic loading is not yet understood. The pile-soil-structure interaction for geothermal foundations is not yet fully quantified, but they show promise in having the possibility to be implemented in many climates.