Global sensitivity analysis on borehole thermal energy storage performances under intermittent operation mode in the first charging phase

It is well recognized that there are many factors influencing the performances of borehole thermal energy storage (BTES). In this paper, the relationship between different kinds of input parameters and four output indicators (i.e. IH, SE, HLP and ED) in the first charging phase was studied by coupling the global sensitivity analysis method and the 3D transient numerical method. Results show that there existed an obvious interaction among different input variables on IH and SE, and the ranking results of factors to the four indicators also vary significantly. The charging temperature and borehole depth are the two key factors to IH and they can explain more than 95% change of IH. Meanwhile, non-linear relationships exist between the intervals of charging time and 1H, and a greater increase of IH is found when it falls in the scope of 5-11.5 h. Unlike IH, the borehole spacing and soil thermal conductivity are critical to SE and HLP, and their influence patterns on SE and HLP are different, e.g. the spacing is positively correlated with the SE and the soil thermal conductivity is negatively correlated with the SE. In addition, the charging temperature alone can explain more than 90% change of ED. (C) 2019 Elsevier Ltd. All rights reserved.