Global Sensitivity Analysis and Uncertainty Quantification for Design Parameters of Shallow Geothermal Systems

Abstract

To improve the design process of geothermal systems, it is important to know which design parameters particularly affect the performance of the system. This article presents investigations on design parameters for borehole heat exchangers in the shallow subsurface. The study is based on numerical simulations with a double U-tube borehole heat exchanger and approximated models obtained using machine learning. As a result of the global sensitivity analysis, relevant parameters are identified and their respective influence on the performance of a borehole heat exchanger is compared. For example, according to this analysis, the three parameters with the highest sensitivity are: the initial temperature, the heat demand and the share of the borehole heat exchanger that is surrounded by groundwater flow. Finally, the effects of uncertainties in the parameters identified as relevant for the design of a borehole heat exchanger are considered in an uncertainty quantification for a fictitious site. Uncertainties for regulatory compliance with respect to temperature limits as well as a large probability of oversizing the system were identified for the considered example. The results of the exemplary uncertainty quantification indicate that it has the potential to be a useful tool for planning practice.

Seepage and Heat Transfer of Dominant Flow in Fractured Geothermal Reservoirs: A Review and Outlook

“…Sisavath et al (2001) characterized the roughness of fractures using symmetrical sinusoidal curves, established the relationships between the average aperture, roughness, and hydraulic resistance coefficient of fractures, and verified the relationships by comparison with relevant model experiments [36]. To quantitatively characterize the fracture roughness, various methods for characterizing the roughness have been proposed, such as statistical parameters, the standard deviation of fracture apertures, and fractal dimension [37][38][39][40][41][42][43]. Accordingly, the effects of rough geometry on the flow and heat transfer have been effectively investigated.…”