Impact of simplifications on numerical modelling of the shallow subsurface at city-scale and implications for shallow geothermal potential.
Impact of simplifications on numerical modelling of the shallow subsurface at city-scale and implications for shallow geothermal potential.
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DOI：
10.1016/j.scitotenv.2021.148236
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发表时间：
2021-06
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通讯作者：
Nikolas Makasis;M. Kreitmair;A. Bidarmaghz;Gareth Farr;Johanna Scheidegger;Ruchi Choudhary
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文献类型：
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作者：
Nikolas Makasis;M. Kreitmair;A. Bidarmaghz;Gareth Farr;Johanna Scheidegger;Ruchi Choudhary
众所周知，浅层地下的人为基础设施，如加热地下室、隧道或浅层地热系统，会增加地面温度，特别是在城市地区。数值模拟有助于了解此类结构的热影响程度及其潜在用途。地下的真实建模通常在计算上是昂贵的，并且需要大量的数据，这些数据通常不容易获得，从而需要使用建模简化。这项工作提出了一个案例研究的城市中心的卡迪夫，英国，高分辨率的数据是可用的，并比较建模结果时，三个关键的建模组件（即地面高程，水力梯度分布和地下室的几何形状）实施“现实”，即与高分辨率的数据，或“模拟”，利用普遍接受的建模假设。结果呈现在一个点（本地）规模和域（聚合）规模的影响，这种简化模型输出不同的目的。与各个位置的测量数据进行比较表明，数值模型的温度输出精度对所实施的水力梯度分布的简化基本不敏感，而基底几何形状的变化对某一点的平均温度预测精度的影响高达3.5 °C。在区域尺度上，前20 m范围内的地面温度显示出显著的增加（约1 °C的体积平均和0.5 °C的表面平均），而在20 m深度处，区域上的平均热通量约为0.06 W/m2。这些增加的温度为浅层地热利用创造了有利条件，每个典型的家庭系统可节省约1700英镑的钻井成本，或增加约9%的热能潜力。基底几何形状和（在较小程度上）水力学的简化可能会导致高估这些温度，因此过度预测地热潜力，而高程简化几乎没有影响。
Anthropogenic infrastructures in the shallow subsurface, such as heated basements, tunnels or shallow geothermal systems, are known to increase ground temperatures, particularly in urban areas. Numerical modelling helps inform on the extent of thermal influence of such structures, and its potential uses. Realistic modelling of the subsurface is often computationally costly and requires large amounts of data which is often not readily available, necessitating the use of modelling simplifications. This work presents a case-study on the city centre of Cardiff, UK, for which high resolution data is available, and compares modelling results when three key modelling components (namely ground elevation, hydraulic gradient distribution and basement geometry) are implemented either ‘realistically’,i.e.with high resolution data, or ‘simplified’, utilising commonly accepted modelling assumptions. Results are presented at a point (local) scale and at a domain (aggregate) scale to investigate the impacts such simplifications have on model outputs for different purposes. Comparison to measured data at individual locations shows that the accuracy of temperature outputs from numerical models is largely insensitive to simplification of the hydraulic gradient distribution implemented, while changes in basement geometry affect accuracy of the mean temperature predicted at a point by as much as 3.5 °C. At the domain scale, ground temperatures within the first 20 m show a notable increase (approximately 1 °C volume-averaged and 0.5 °C surface-averaged), while the average heat flux over the domain is about 0.06 W/m2at 20 m depth. These increased temperatures result in beneficial conditions for shallow geothermal utilisation, producing drilling cost savings of around £1700 per typical household system or about 9% increase in thermal energy potential. Simplifications of basement geometry and (to a lesser degree) the hydraulics can result in an overestimation of these temperatures and therefore over-predict geothermal potential, while the elevation simplification showed little impact.