Energy performance and thermal impact of a Borehole Heat Exchanger in a sandy aquifer: Influence of the groundwater velocity

On the applicability of the moving line source theory to thermal response test under groundwater flow: considerations from real case studies

“…Although this output can be overwhelming, it has to be noticed that the highest Darcy velocity taken from this family of solutions Péclet number, calculated by taking the borehole radius as the characteristic length, is about 0.1. According to the study by Angelotti et al (2014), reporting also similar results from literature, when Pé = 0.1 groundwater influence on the borehole annual energy performance is limited to a maximum of 20%. Therefore, it can be argued that an inaccurate estimation of the Darcy velocity in this range does not affect significantly the borehole heat exchanger design, although further studies are necessary to clarify this issue.…”

“…The issue of the non-uniqueness of the solutions, namely the existence of several possible pairs of thermal conductivity and Darcy velocity values, is addressed in practice through physical considerations. Finally on the basis of a previous study by the authors (Angelotti et al 2014), the impact of the uncertainty in the Darcy velocity is discussed, in terms of variation in the expected borehole energy performance.…”

A Numerical Study on the Impact of Grouting Material on Borehole Heat Exchangers Performance in Aquifers

“…In any stress period, the transient time step was set equal to a maximum of 0.024 days (34 min). In accordance with Hecht-Mendez et al [38], previous simulations carried out with this model [6] demonstrated that MT3DMS can be used to predict the thermal impact and the energy performance of such systems with good accuracy, comprehensively simulating the U-pipe geometry and the heat carrier fluid. Details about the model validation under different groundwater flow velocities can be found in Angelotti et al [6].…”

“…The case study refers to a typical BHE, consisting of a 100 m polyethylene U-pipe with an internal diameter of 0.04 m and a pipe-to-pipe centerline distance of 0.06 m, as in Angelotti et al [6]. The U-pipe is a 200 m deep saturated sandy aquifer, assumed homogeneous with an hydraulic conductivity of 2 × 10 −4 m/s, a frequent value detected in the Po Plain area [35,36].…”

“…The previously validated model [6] is used here to evaluate the influence of the back-filling grout on the seasonal energy performance and on the temperature distribution in the subsoil. For this reason three main cases are compared (Table 3), differing for the back-filling material inserted in the 12.5 cm diameter borehole:…”