Energy Piles in Cooling Dominated Climates



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Air pollution is one of the main environmental problems mankind faces in the 21^(st) century caused by to the extensive use of fossil fuels. One of the opportunities to overcome this problem is to develop new technologies and methods to profit from the energy stored in the ground. A promising high-efficiency technology for the thermal control of buildings is the shallow geothermal energy. This technology is growing rapidly because it consumes less conventional energy for operation, which in turn results in fewer CO_(2) emissions. This technology harnesses constant and moderate ground temperature for thermal control of a building using foundation piles. Outside air temperature changes with the season, while ground temperature remains moderate and constant. In summer, ground temperature is lower than air temperature, and so the ground may be used as a heat sink. The opposite is true in winter; the ground becomes a heat source. This technology is used efficiently in cold, heating dominated climates. Could this be true in hot, cooling dominated climates?

To achieve the ultimate goal and answer the above question, this study considered the different elements of a full SGES, namely: soil, climate, energy pile, and ground source heat pump. First, The need for a new, easy, and quick in-situ method to thermally characterize soils lead to the development of the Thermal Cone Test. Second, the soil-climate interaction and its effect on the thermodynamic efficiency of energy piles was an important factor to consider, where the decrease in soil saturation leads to a decrease in the heat exchange rate of energy piles. Third, the thermal use of foundation pile changes the pile and surrounding soil temperature where both materials are temperature dependent. This change in temperature leads to a change in the mechanical behavior of energy piles. Fourth, a full-scale test on installed and instrumented energy piles group was needed to understand the thermodynamics of a full system and to provide experimental data for a full economic study. Finally, this study was capped by an economic analysis to evaluate the cost, benefits, payback period, and feasibility of SGES in cooling dominated climates.

The study presented in this dissertation found that integrating energy piles in heating and cooling systems in hot, cooling dominated climates could be economical and environmentally friendly solution, but attention should be paid to the thermodynamic efficiency of the system when unsaturated soil layer is encountered, and to the long term mechanical behavior of foundation piles in high plasticity clay where additional settlement could take place resulting from the increased creep rate caused by soil heating.