Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, UK.
Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, UK.
Sci Total Environ. 2021 Oct 15;791:148236. doi: 10.1016/j.scitotenv.2021.148236. Epub 2021 Jun 8.
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/m at 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.
人为的浅层地下基础设施，如加热地下室、隧道或浅层地热系统，已知会增加地面温度，特别是在城市地区。数值模拟有助于了解这些结构的热影响范围及其潜在用途。对地下进行真实模拟通常计算成本高，需要大量数据，而这些数据通常不易获得，因此需要采用建模简化。这项工作以英国卡迪夫市中心为案例研究，因为这里有高分辨率数据，并比较了在三种关键建模组件（即地面高程、水力梯度分布和地下室几何形状）分别以“真实”（即高分辨率数据）或“简化”（利用常用建模假设）方式实施时的建模结果。结果以点（局部）尺度和域（总体）尺度呈现，以研究这些简化对不同目的模型输出的影响。与个别地点的实测数据进行比较表明，数值模型的温度输出精度在很大程度上不受所实施的水力梯度分布简化的影响，而地下室几何形状的变化会影响到点预测平均温度的准确性，其变化幅度高达 3.5°C。在域尺度上，前 20 米内的地面温度显示出明显的升高（体积平均约为 1°C，表面平均约为 0.5°C），而整个域的平均热通量在 20 米深处约为 0.06 W/m。这些温度升高为浅层地热利用创造了有利条件，可为每个典型家庭系统节省约 1700 英镑的钻探成本，或增加约 9%的热能潜力。地下室几何形状的简化（以及在较小程度上水力的简化）可能导致这些温度的高估，从而高估地热能潜力，而高程简化的影响则较小。
