GOALI: Long-Term Thermo-Mechanical Performance and Group Effect Considerations for Design of Energy Piles

主要是由于能源需求增加、自然资源枯竭和化石燃料消费产生的碳排放的不利影响，全球越来越倾向于利用替代能源。 地球近地表蕴藏着巨大的地热能，可用于加热和冷却。 在大约10米的深度以下，季节性地面温度与外部空气温度相比保持稳定，通常在10-18° C之间。 可以使用由埋管（即，“地热回路”）填充有乙二醇-水混合物，该乙二醇-水混合物使用地源热泵在结构和地下之间循环。 在过去的20年里，这种地面耦合概念已经从主要的住宅应用扩展到大型项目。 特别令人感兴趣的是地热回路已被集成到深基础元件中的应用，例如桩，墩或钻孔轴。 这些系统被称为能量桩，用于已经需要深基础进行结构支撑的软土中。 地热循环的集成几乎没有额外的成本。 能量桩具有适用于任何气候或地区的优点，包括风能和/或太阳能效率有限的地区。 在理想的条件下，能源桩可以显着减少碳足迹，降低供暖和制冷成本，并将建筑物的能源使用量降低80%。 虽然能源桩在过去十年中在欧洲和日本呈指数级增长，但在美国却很少受到关注。 这部分是由于缺乏对它们的好处的认识，沿着的是缺乏证明其成本效益的美国案例研究。 还有一些与它们的热和热机械行为有关的问题，必须在它们的设计完全优化之前回答。 主要问题是缺乏标准化的实地测试程序，以及缺乏涵盖广泛气候和土壤条件的长期业务研究。 本研究的主要目的是调查长期的能源桩行为，并制定新的能源桩设计准则。 该项目将在美国五个地点进行现场测试，沿着先进的数值模拟，以及技术转让和推广。 在现场测试期间，测试的能量桩将被加载以模拟建筑物负载以及由于热交换操作引起的温度变化的综合效应。 除了对单个桩进行现场测试外，还将在其中一个站点测试一组9个能量桩的热交换行为，以更好地了解能量桩的组效率。 现场测试的实验结果将用于校准先进的数值模型，该模型在一系列参数分析中模拟长期的能量桩行为。这项研究是与几个工业参与者以及非营利组织和政府机构合作进行的。 一些工业参与者正在提供实物捐助，进行全面的实地测试，捐赠材料、仪器和热泵。 三家基础工程承包商（Berkel、撒切尔和Layne GeoConstruction）正在安装能量桩并协助现场测试。 地热回路的管道和现场测试的热泵将分别由REHAU和WaterFurnace提供。 Geo-Instruments，Inc.正在协助现场仪表和数据采集，并为现场测试提供必要的传感器。 美国绿色建筑理事会、深基础研究所和联邦公路管理局等几个非营利组织和政府机构正在参与审查调查结果，提供指导，并帮助将结果扩大到工程界和其他领域。主要的智力价值是，这项大学与工业界的合作将回答有关长期热机械和能量堆组性能的关键问题，并提供新的工业设计指南和现场测试程序。 就更广泛的影响而言，这项工作将有助于促进能源桩技术在美国的使用，从而有助于减少化石燃料消耗，降低温室气体排放，降低供暖和空调成本，并减少我们对外国能源的依赖。

There is a growing global trend to utilize alternative energy resources mainly driven by rising energy demand, depleting natural resources and adverse effects of carbon emissions from fossil fuel consumption. The earth's near surface contains a huge potential of stored geothermal energy that can be used for heating and cooling. Below a depth of about 10 m, seasonal ground temperatures remain stable compared to outside air temperatures, typically lying between 10-18° C. This near surface heat energy can be efficiently accessed using heat exchangers consisting of buried pipes (i.e., "geothermal loops") filled with a glycol-water mixture that is circulated between the structure and the subsurface using a ground source heat pump. Over the past 20 years, this ground coupling concept has been expanded from mainly residential applications to large-scale projects. Of particular interest is the application where geothermal loops have been integrated into deep foundation elements, such as piles, piers, or drilled shafts. These systems, referred to as Energy Piles, are used in soft soils where deep foundations are already needed for structural support. The integration of the geothermal loops comes at little additional cost. Energy Piles have the advantage of being applicable in any climate or region, including those where wind and/or solar power have limited effectiveness. In ideal conditions, Energy Piles can significantly reduce carbon footprint and lower heating and cooling costs and energy use for buildings by as much as 80%. Although Energy Piles have seen exponential growth in Europe and Japan over the last decade, they have received little attention in the US. This is partly due to a lack of awareness about their benefits, along with a lack of US case studies that demonstrate their cost-effectiveness. There are also questions related to their thermal and thermo-mechanical behavior that must be answered before their designs can be fully optimized. The main issues involve a lack of standardized field testing procedures and a lack of long-term operational studies that cover a wide range of climatic and soil conditions. The main purpose of this study is to investigate long-term Energy Pile behavior and to develop new Energy Pile design guidelines. The project will involve field testing at five sites across the US, along with advanced numerical modeling, and technology transfer and outreach. During the field tests, the tested Energy Pile will be loaded to simulate the combined effect of the building load as well as the temperature changes due to heat exchange operations. In addition to field tests on individual piles, the heat exchange behavior of a group of 9 Energy Piles will be tested at one of the sites to better understand the group efficiency of Energy Piles. Experimental results from the field tests will be used to calibrate the advanced numerical models that simulate long term Energy Pile behavior in a series of parametric analyses.This study is conducted in partnership with several industrial participants as well as non-profit organizations and government agencies. Several industrial participants are providing in-kind contributions by building full-scale field tests, donating materials, instrumentation and heat pumps. Three foundation engineering contractors (Berkel, Thatcher and Layne GeoConstruction) are installing Energy Piles and assisting with the field testing. Piping for the geothermal loops and heat pumps for the field tests will be provided by REHAU and WaterFurnace, respectively. Geo-Instruments, Inc. is assisting with field instrumentation and data acquisition, and providing the necessary sensors for the field tests. Several non-profit organizations and government agencies such as the US Green Building Council, the Deep Foundations Institute, and the Federal Highway Administration are participating by reviewing the findings, providing guidance, and helping to broaden dissemination of the results to the engineering community and beyond.The main intellectual merit is that, this university-industry collaboration will answer key questions about long-term thermo-mechanical and Energy Pile group performance, and provide new industry design guidelines and field testing procedures. In terms of broader impact, the work would help promote the use of Energy Pile technology in the United States, and thereby help reduce fossil fuel consumption, lower greenhouse gas emissions, lower the cost of heating and air conditioning, and decrease our reliance on foreign energy.