Non Steady Analytical Models for Energy Pile Testing and Design

欧洲的建筑存量以每年约1%的速度增加。这意味着运营能源需求同比增加超过450万吨油当量。在这些能源需求中，多达四分之三与空间供暖（或制冷）有关，约占欧洲和北美能源使用总量的一半。地源热泵可以将空间供暖的净能耗减少约75%，因此可以在应对能源和碳排放挑战方面发挥重要而及时的作用。尽管迫切需要遏制新建筑不断增长的能源需求，但地源热泵系统市场仍面临着许多扩张障碍。虽然有些障碍与监管有关，但投资成本密集度仍然是一个重要因素。因此，研究和开发必须侧重于提高能源效率和降低资本成本。降低投资资本成本的一种途径是通过组合使用用于系统的热交换器部件的建筑地基，从而避免了对诸如钻孔的特殊用途热交换器的构造的需要。这有可能既减少资本支出，又增加每钻米换热器的能量。桩是最常见的深基础类型。这些通常是通过钻一个洞，填充混凝土和钢筋。能量桩是一个术语，用于一个基础桩，它配备了传热管，作为地源热泵系统的热交换器部分。能源桩于1984年在奥地利首次试验，但热分析和设计方法大大落后于实际应用。最近的突破表明，在短期基础上储存热能的桩的混凝土部分的重要性。这是重要的，因为波动的操作能量需求意味着很少实现桩中的热稳定状态。尽管如此，大多数常规的设计方法仍然根据稳态热阻参数来计算能量堆。这意味着混凝土中的任何能量储存都被忽视，系统的能量容量通常被低估。事实上，稳态假设已被证明低估了约20%的潜在能源节省从能源桩。该提案概述了计划开展的工作，这些工作将开发新的非稳态模型，用于能源堆的热分析。这项工作还将包括这些模型的应用，在现场热响应测试，用于确定桩周围土壤的热特性。因此，新的模型将有助于改善土壤参数的选择和不太保守的设计方法。这项工作是新颖的，因为目前没有分析模型，适当地模拟能源桩的瞬态行为。通过引入适当的非稳态模型，这项工作将导致改进和不太保守的评估能量桩可用的能量，从而增加其在实践中的吸收。这项工作是紧迫的，因为使用不适当的稳态模型的替代方案将导致地源热泵系统性能的预测不足，从而抑制这一关键的可再生热技术的吸收。

Europe's building stock is increasing in floor area by approximately 1% per annum. This represents an additional operational energy demand of over 4.5 million tonnes of oil equivalent, year on year. Of that energy requirement up to three quarters is related to space heating (or cooling), representing about half of total energy usage in Europe and North America. Ground source heat pumps, which can reduce the net consumption of energy for space heating by approximately 75%, can therefore play a significant and timely role in tackling the energy and carbon emissions challenge. Despite the urgent need to curb the increasing energy requirements of new buildings, the market for ground source heat pump systems faces a number of barriers to expansion. While some of the barriers are related to regulation, investment cost intensity remains an important factor. Consequently, research and development must focus on increasing energy efficiency and reducing capital costs. One route to reducing investment capital costs is through the combined use of building foundations for the heat exchanger component of the system, thereby avoiding the need for construction of special purpose heat exchangers such as boreholes. This has the potential to both reduce capital expenditure and deliver increased energy per drilled metre of the heat exchanger. Piles are the most common type of deep foundation. These are typically constructed by augering a hole which is infilled with concrete and steel reinforcement. Energy pile is the term used for a foundation pile which is equipped with heat transfer pipes to act as the heat exchanger part of a ground source heat pump system. Energy piles were first trialled in Austria in 1984, but thermal analysis and design methods have lagged substantially behind the practical application. Recent breakthroughs have shown the importance of the concrete part of the pile in storing thermal energy on a short term basis. This is significant because fluctuating operational energy demand means that a thermal steady state in the piles is rarely achieved. Despite this, most routine design approaches still characterise energy pile in terms of a steady state thermal resistance parameter. This means that any storage of energy in the concrete is neglected and the energy capacity of the system is routinely underestimated. Indeed, the steady state assumption has been shown to underestimate the potential energy saving available from energy piles by around 20%. This proposal outlines planned work which will develop new non-steady models for use with the thermal analysis of energy piles. The work will also include application of these models to in situ thermal response tests which are used to determine the thermal characteristics of the soil surrounding the pile. Hence the new models will contribute to both improved soil parameter selection and less conservative design approaches. This work is novel because there are currently no analytical models that appropriately simulate the transient behaviour of energy piles. By the introduction of appropriate non steady models this work will lead to improved and less conservative assessment of energy available from energy piles and hence increase their uptake in practice. This work is pressing because the alternative of using inappropriate steady state models will result in the under-prediction of ground source heat pump system performance and thereby inhibit uptake of this key renewable heat technology.