A dimensionless parameter approach to the thermal behavior of an aquifer thermal energy storage system

Abstract

To predict the performance of an aquifer thermal energy storage system, an understanding of the system's hydrothermal behavior is needed. One possibility is to run a detailed numerical simulation of the system. However, for a single-well system in which fluid flow is limited to steady radial flow, a characterization scheme based on a set of four dimensionless parameter groups allows production temperatures and energy recovery factors to be read from graphs. The assumption of radial fluid flow is valid when buoyancy flow can be neglected and a well is fully screened in a horizontal aquifer which is confined above and below by impermeable layers. Criteria for little buoyancy flow include a low permeability or vertically stratified aquifer, a small temperature difference between injected and ambient water. and short cycle leneth The ha.•ie enerov tranannrt ., ,.., ........ •,.• ....... r layer system with steady radial fluid flow in the aquifer are nondimensionalized to derive the key parameter groups. Next a numerical model which calculates the heat transfer in the aquifer and confining layers for an injection-storage-production cycle is run for a range of values of these groups. The calculated production temperatures and energy recovery factors are then presented graphically as a function of the parameter groups. Comparisons between results of field experiments and recovery factors read from the graphs show good agreement. ATES cycl• [Tsang eta!., 1977; Fabris et al., 1977]. Recently, Sauty et al. [1980a] have studied the thermal behavior of a simplified single-well ATES system in terms of , a set of dimensionless groups. A few heat storage field experiments in either confined

The effect of a density gradient in groundwater on ATES system efficiency and subsurface space use

“…This is, however, compensated for by a smaller thermal radius, which limits these buoyancy losses, especially for monowell systems. To obtain the highest recovery efficiency, the results indicate that in case of buoyancy flow, the optimal L/R th -ratio has to be chosen smaller than the thresholds identified by Doughty et al (1982) and Bloemendal and Hartog (2018). For monowells it is more important to prevent short-circuit flow between the screens, which requires sufficient spacing between the top and bottom screen.…”

“…In this study the thermal energy stored is referred to as heat or thermal energy; however, all the results discussed equally apply to storage of cold water used for cooling. As in other ATES studies (Doughty et al, 1982;Sommer et al, 2015), the recovery efficiency (η th ) of an ATES well is defined as the amount of injected thermal energy that is recovered after the injected volume has been extracted. For this ratio between extracted and infiltrated thermal energy (E out /E in ), the total infiltrated and extracted thermal energy is calculated as the cumulated product of the infiltrated and extracted volume with the difference of infiltration and extraction temperatures ( T = T in − T out ) for a given time horizon (which is usually one or multiple storage cycles), as described by:…”

“…This mechanism causes the interface between injected and ambient water to remain vertical in the middle of the aquifer, where the density of the injected water practically equals that of the ambient groundwater at that depth. The injected heat will cause a sharp temperature interface with the ambient groundwater due to thermal retardation (Doughty et al, 1982;Bloemendal and Hartog, 2018) and the fact the spreading of heat is conduction dom- Figure 3. Schematic representation of disturbance of a density gradient by warm well of a doublet (a) and monowell (b) ATES system.…”

“…Since losses due to mechanical dispersion and conduction occur at the boundary of the stored body of thermal energy, the thermal recovery efficiency therefore depends on the geometric shape of the thermal volume in the aquifer (Doughty et al, 1982). Following Doughty, the infiltrated volume is simplified as a cylinder with a thermal radius (R th ) is defined as:…”

“…Different design strategies are now evaluated to firstly identify the relative contribution of conduction, dispersion and buoyancy losses and secondly, to identify possible controls to maximize overall efficiency. Doughty et al (1982) and Bloemendal and Hartog (2018), use the ratio of screen length over thermal radius (L/R th ) as a design criterion to ensure maximum heat-recovery efficiency. They found that this ratio should be between 1 and 4.…”