Abstract
A research project was developed in Spain to undertake some studies on the geothermal use of pile foundations (PITERM PROJECT). The experiment consists of a specifically designed, constructed and fully monitored geothermal precast pile driven at Polytechnic University of Valencia. An important distinctive feature of the developed pile was the fact that it was assembled from two identical sections connected with a specific joint, developed by Rodio-Kronsa. This allows the installation of much longer precast piles into the ground. The pile is under two types of loads: mechanical and thermal. The mechanical load was applied by means of a mechanical frame anchored to the ground and three additional anchors used to induce an active compressive force. The thermal load was produced by means of a thermal rig able to inject heat or extract heat from the pile at any desired programable heat injection/extraction rate. One of the features of this precast pile is its geometry, similar to a single U borehole heat exchanger (BHE) which is not common in thermoactive piles, usually equipped with probes attached to the armatures. In our study, we have characterized the thermal behaviour of the precast pile experimentally and simulated its temperature response by means of a TRNSYS model. This article describes part of a test series carried out where the mechanical and thermal behaviour of a pile subjected to thermal and mechanical loads simulating a real pile in a building was studied. Therefore, this publication has only focused on the thermal performance of the pile and its thermal modelling by computer. From this model, the thermal parameters of the soil–pile system have been extracted and compared with those of a single standard single U BHE. In essence, our assessment points to a quite similar thermal behaviour of the studied precast pile compared to a conventional single U borehole heat exchanger of the same length and equivalent diameter, while the installation costs of such elements would be substantially lower due to its double, structural and thermal, function.
Highlights
IntroductionEnergy piles (thermo-active piles or geothermal piles) are foundations with double usefulness: to support the loads of the building and to serve as a heat exchanger with the ground
Energy piles are foundations with double usefulness: to support the loads of the building and to serve as a heat exchanger with the ground
A service thermal load test was performed injecting heat into the heat exchanger simulating that the pile was part of a ground coupled heat exchanger of a shallow geothermal heat pump system working in cooling mode in a tertiary building (Section 3.2)
Summary
Energy piles (thermo-active piles or geothermal piles) are foundations with double usefulness: to support the loads of the building and to serve as a heat exchanger with the ground. The key factor in the sustainability of thermo-active foundations systems is utilizing geo-structures that are already needed for structural purposes This way, coupling piles with ground source heat pumps only requires a low extra over cost for Energies 2017, 10, 1315; doi:10.3390/en10091315 www.mdpi.com/journal/energies. Energies 2017, 10, 1315 shallow geothermal heat pump systems, and it supposes a minimal impact on the piling program. They constitute a growing energy technology that improve the energy efficiency of heating and cooling systems in building and have been widely developed and researched in recent years [1,2,3,4,5,6]. As this is a relatively new technology, robust standards and guidelines have not yet been developed for the design of these systems
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