Philippe Pasquier

Stochastic interpretation of thermal response test with TRT-SInterp

A program designed to analyze thermal response tests by deterministic or stochastic inversion is presented. In its current state, the program treats variable heating power signals and emulates a borehole heat exchanger by a finite line-source model or a thermal resistance and capacity model. The possibly unknown parameters identified may comprise the thermal conductivity and volumetric heat capacity of the ground or grout, as well as the pipes spacing and initial ground temperature. If the thermal resistance and capacity model is used as the interpretation model, it is possible to integrate to the inversion the temperature measurements made at various depths in the fluid and grout and to take into account the thermal capacity of the underground components and the fluid flow rate. The program is tested under real field conditions by using the temperature measurements recorded by 18 probes installed at various depths in a borehole heat exchanger during a thermal response test. The test results indicate a relative insensitivity of the fluid temperature to the ground volumetric heat capacity and suggest that it is currently illusive to try identifying its real value from a conventional thermal response test.

Standing column wells

Standing column well (SCW) systems present a strong potential for energy savings, especially in dense urban areas with suitable geological conditions where lack of space constitutes an impediment to the use of closed-loop systems. This chapter aims at presenting some design considerations and recent advancements relative to the thermal, hydraulic, and chemical simulation of SCWs and identifies specific research needs to foster their use. It is shown how a thermal resistance and capacity model can assess the performance of a hybrid system operated under different bleed ratios in a fractured aquifer. Additionally, this chapter shows how to perform coupled thermo-hydrogeochemical simulation to predict the dissolution and precipitation of calcite that occurs along the well as a function of operating conditions. The approach helps to foresee possible operation problems with the SCW and to select suitable mitigation measures to sustain long-term performance of SCW.

Interpolation of Concentration Measurements by Kriging Using Flow Coordinates

Groundwater contaminant plumes frequently display a curvilinear anisotropy, which conventional kriging and geostatistical simulation approaches fail to reproduce properly. In many applications, physically relevant coordinate transformations are used to modify the relationships between data points and simplify the specification of nonlinear anisotropy. In this paper, we present a kriging approach that uses a coordinate transformation to improve the interpolation of contaminant concentrations. The proposed alternative flow coordinates (AFC) consist in the hydraulic head and one (2D) or two (3D) streamline-based coordinates. In 2D, the mapping obtained using AFC is similar to that yielded by the natural coordinates of flow (i.e. hydraulic head and stream function). AFC can be generalized to 3D flow and to the presence of wells, which is not the case with the natural coordinates. The performance of the approach is investigated using a simple 3D synthetic case. Kriged concentration maps obtained with the AFC reproduce the curvilinear features found in the reference plume. Performance statistics suggest AFC improves plume delineation compared to conventional kriging on a Cartesian grid. However, the performance of the AFC transformation is limited by the fact that, while it accounts for advection, it does not consider the effects of dispersion on the shape of the plume. This aspect and further testing on complex cases is the subject of ongoing research.

A comparison of numerical simulation methods analyzing the performance of a ground-coupled heat pump system

Ground-coupled heat pumps are increasingly being utilized to heat and cool buildings. Although it is difficult to size and to predict their behavior and performance, their design can be optimized via simulations. EnergyPlus is a popular energy simulation program for modeling building heating and other energy flows and, since it is organized to consider borehole heat exchangers via the well-known g-functions approach, it can be used advantageously for that purpose. The Capacity Resistance Model is another recent numerical simulation tool devoted to ground and borehole heat exchangers. In this work, two methods to calculate the g-fucntions were analyzed, using as case-study a real office building, whose imbalance between the heat extracted and injected into the ground was found to be appreciable. The energy imbalance involves a ground temperature drift affecting the system efficiency. The results of the EnergyPlus g-functions and the Capacity Resistance Model model approaches were compared. The capacity of the two methodologies to accurately simulate this phenomenon were analysed also with reference to the available buildings long-term monitoring data. The analysis showed the importance of using g-functions suitable to reflect the layout of the borehole field, in order to correctly evaluate the energy performance of the entire ground source heat pump system.