Abstract Standard thermal response tests (TRT) are typically carried out to evaluate subsurface thermal parameters for the design and performance evaluation of borehole heat exchangers (BHE). Typical interpretation methods apply analytical or numerical solutions, which assume that the ground is homogeneous, isotropic and infinite. However in reality, the underground is commonly stratified and heterogeneous, and therefore thermal properties might significantly vary with depth. Thus, novel instruments and methods are necessary to characterize thermo-physical properties along the BHE. In this study, two novel in-borehole temperature measurement instruments, Geoball and Geowire, are assessed during the performance of a distributed TRT (DTRT). The latter is evaluated in comparison to the widely used fiber optical thermometers. Our results suggest that both novel instruments have several advantages. For instance, both devices are able to instantaneously measure temperature with a higher spatial resolution. In addition, our study evaluates two methods to estimate depth-specific thermal conductivities: (1) a computer program based on infinite line source (ILS) approach and (2) a recently suggested inverse numerical procedure. For the latter less data is required, while demonstrating an accurate resolution to even detect thin conductive geological layers. Moreover, the average value of the depth-specific local effective estimates for both methods is significantly close to the effective subsurface conductivity of 3.20 W/m-K calculated based on standard TRT: 1.27 % below for the computer program and 0.28 % below for the numerical procedure.

中文翻译：

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估计埋管换热器中特定深度热特性的新仪器和方法

摘要 标准热响应测试 (TRT) 通常用于评估埋入式换热器 (BHE) 设计和性能评估的地下热参数。典型的解释方法应用解析解或数值解，假设地面是均匀的、各向同性的和无限的。然而实际上，地下通常是分层的和异质的，因此热特性可能会随着深度的不同而显着变化。因此，需要新的仪器和方法来表征沿 BHE 的热物理特性。在这项研究中，在分布式 TRT (DTRT) 的性能期间评估了两种新型井内温度测量仪器 Geoball 和 Geowire。后者是与广泛使用的光纤温度计进行比较的。我们的结果表明，这两种新型仪器都有几个优点。例如，这两种设备都能够以更高的空间分辨率即时测量温度。此外，我们的研究评估了两种估计特定深度热导率的方法：(1) 基于无限线源 (ILS) 方法的计算机程序和 (2) 最近建议的逆数值程序。对于后者，需要的数据较少，同时展示了甚至可以检测薄导电地质层的准确分辨率。此外，两种方法的特定深度局部有效估计的平均值明显接近基于标准 TRT 计算的 3.20 W/mK 的有效地下电导率：计算机程序低于 1.27%，数值程序低于 0.28% .