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

主要受能源需求上升、自然资源枯竭以及化石燃料消费产生的碳排放的不利影响的推动，利用替代能源的全球趋势日益明显。地球近地表蕴藏着巨大的地热能储存潜力，可用于加热和冷却。在大约10米的深度以下，季节性地面温度与室外气温相比保持稳定，通常在10-18°C之间。这种近地表热能可以通过由埋管(即“地热回路”)组成的热交换器有效地获取，该热交换器填充乙二醇水混合物，利用地源热泵在建筑物和地下之间循环。在过去的20年里，这种地面耦合的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循环已集成到深层基础元素中的应用，如桩、桥墩或钻孔。这些系统被称为能量桩，用于软土中，在那里已经需要深基础来进行结构支撑。地热环路的集成几乎没有额外的成本。能源堆具有适用于任何气候或地区的优势，包括那些风能和/或太阳能效率有限的地区。在理想条件下，能源堆可以显著减少碳足迹，并将建筑物的供暖和制冷成本以及能源使用量降低高达80%。尽管能源储备在过去10年里在欧洲和日本呈指数级增长，但在美国却鲜有人关注。这在一定程度上是因为缺乏对其好处的认识，以及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得到回答。主要问题包括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。这项研究的主要目的是研究能量桩的长期行为，并制定新的能量桩设计指南。该项目将包括在美国各地的五个地点进行实地测试，以及先进的数值建模、技术转移和推广。在现场测试过程中，将对测试的能量桩进行加载，以模拟建筑荷载以及热交换操作引起的温度变化的综合影响。除了对单个桩进行现场测试外，还将在其中一个场地测试9根能量桩的换热性能，以更好地了解能量桩的群体效率。现场测试的实验结果将被用来在一系列参数分析中校准模拟长期能量堆行为的高级数值模型。这项研究是与几个行业参与者以及非营利组织和政府机构合作进行的。几个行业参与者正在通过建立全面的实地测试、捐赠材料、仪器和热泵来提供实物捐助。三家基础工程承包商(Berkel、Thatcher和Layne GeoConstruction)正在安装Energy桩并协助现场测试。用于现场测试的地热回路和热泵的管道将分别由REHAU和Water Furnace提供。Geo-Instruments公司正在协助现场仪器和数据采集，并为现场测试提供必要的传感器。几个非营利性组织和政府机构，如美国绿色建筑委员会、深层基础研究所和联邦公路管理局，通过审查调查结果，提供指导，并帮助向工程界和其他方面更广泛地传播结果，参与其中。主要的学术价值是，这种大学和行业的合作将回答有关长期热力机械和能量桩组性能的关键问题，并提供新的行业设计指南和现场测试程序。从更广泛的影响来看，这项工作将有助于在美国推广能源堆技术，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.