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Ground source heat pump (GSHP) systems have been considered to be a low-carbon technology to provide heating and cooling for buildings in urban environments. This study focuses on the short-and long-term evolution of groundwater temperature induced by high-density GSHP installations in an urban residential area in Cologne, Germany. Specifically, a 2D heat transport model considering both thermal convection and conduction has been constructed using the finite element simulator OpenGeoSys. The simulated temperature changes within the initial few years were compared to the monitored dataset, while the GSHP heating load and thermal conductivity were calibrated. Subsequently, the validated model was run for 25 years to evaluate the long-term trend of the subsurface temperature. Also, effects of model uncertainties were explored with different simulated scenarios. Results indicate that sufficiently large groundwater flow and a high cooling ratio can effectively mitigate ground cooling. Based on these findings, best and worst-case scenarios were formulated for the studied case and the sustainability of GSHP operation were evaluated accordingly. As an outcome, specific design and operation criteria were proposed for the sustainable utilization of shallow geothermal energy for the heating and cooling of buildings in urban areas.

Thermochemical heat storage devices based on water adsorption on microporous materials are a viable option for heat storage applications. The Dubinin-Polanyi theory of micropore filling has been widely applied for the thermodynamical characterization of various adsorption working pairs. It has been used for the deduction of adsorption enthalpies from adsorption equilibrium data. How well the theory predicts the dependence of storage densities on the storage cycle characteristics remains to be clarified as it is vital for technology assessment and design. This study compares the heat storage densities predicted by the Dubinin-Polanyi theory to experimentally determined data of two granulated zeolite samples, namely a Na-X and a Ca-X, under various humidity conditions.

The study of water sorption in microporous materials is of increasing interest, particularly in the context of heat storage applications. The potential-theory of micropore volume filling pioneered by Polanyi and Dubinin is a very useful tool for the description of adsorption equilibria. Based on one single characteristic curve, the system can be extensively characterised in terms of isotherms, isobars, isosteres, enthalpies etc. However, the mathematical description of the adsorbate density's temperature dependence has a significant impact especially on the estimation of the energetically relevant adsorption enthalpies. Here, we evaluate and compare different models existing in the literature and elucidate those leading to realistic predictions of adsorption enthalpies. This is an important prerequisite for accurate simulations of heat and mass transport ranging from the laboratory scale right up to the reactor level of the heat store.

Thermal energy storage technologies are of current interest in order to improve the integration of renewable energy sources as well as energy efficiency. Numerical simulations of thermochemical heat storage are especially challenging and time consuming due to the complexity of the mathematical description of the strongly coupled and highly nonlinear processes characteristic for such systems. These difficulties are exacerbated once practically relevant complex or large geometries are considered as they can occur around heat exchangers or due to internal heterogeneities of the reactive bed. To allow a computationally efficient simulation of such applications, an existing finite element implementation of a thermochemical heat storage model was parallelised using PETSc routines. Input/output, global assembly and the linear solver all work in a distributed fashion. The approach is implemented into the open source framework OpenGeoSys. The performance of the present parallelisation approach is tested by simulating the discharge of a heat store based on calcium-oxide and water as a benchmark problem. The computational time required for the simulation could be reduced significantly.

CO2 capture and storage technology is often hampered by CO2 leakage through natural occurring fractures in the overlying caprock. This work suggests a two-dimensional test case of typical CO2 injection with possible leakage into freshwater resource. By using this test case in combination with a 1D verification example, the effects of sorption and decay processes are evaluated. Leakage value and buoyancy number reveal that buoyancy is the main mechanism for leakage, and the sorption process delays the arrival of CO2 at the fracture. The volume translated Peng-Robinson (VTPR) equation of state (EoS) has been modified for accurate material properties of CO2 and water in a multi-componential flow model.

In this paper, conceptual modeling and numerical simulation of two-phase flow during CO2 injection into deep saline aquifers is presented. The work focuses on isothermal transport and deformation processes in the vicinity of the injection well including hydromechanical failure analysis. Governing differential equations are based on balance laws for mass and momentum completed by constitutive relations for the fluid and solid phases as well as their interactions. Constraint conditions for the partial saturations and the pressure fractions of CO2 and brine are defined. To characterize the stress state in the solid matrix the effective stress principle is applied. The coupled problem is solved using an in-house scientific finite element code, and verified with benchmarks. In terms of application-oriented aspects, we examine the mechanical integrity of a deep saline aquifer during the injection of supercritical CO2. The analysis is conducted with a numerical scheme of the capillary pressure and non-wetting phase pressure for the two-phase flow process. In this study, unidirectional hydromechanical coupling is considered. Caprock stability is monitored in time, referenced to the potential for hydraulic fracture and shear slip along an optimally oriented shear plane for a suite of injection pressures. For reasonable parameter values and the chosen aquifer geometry, significant mechanical failure (and potential breach of integrity) is expected in the shale caprock for all but low injection rates. This indicates that the analysis of the hydromechanical response is crucial for proper selection of injection sites, injection rates, and total storage capacity.

This paper presents non-isothermal effects on disposal of carbon dioxide into a saline aquifer. Carbon dioxide storage in the subsurface could be an important part of the present climate control initiative to reduce the carbon dioxide concentration of the atmosphere. Layer of water-bearing permeable rock is assumed as a saturated porous medium, and the contained water can be replaced by compressed carbon dioxide. In such environment, water vapor flow can be developed from the thermal gradient caused by geothermal energy. High injection pressure is required to remove the fluid already present in the pores of solid skeleton hence accurate density calculation is important. So we use an extended ideal gas law to calculate the compressed carbon dioxide gas density. Temperature dependent entry pressure is accounting the surface tension and wetting angle role on the sorption equilibrium. Governing equations for numerical simulations are: mass balance equations for each component, i.e., water, vapor and carbon dioxide; energy balance equation. We have used a combined monolithic and staggered coupling scheme to solve these equations numerically using an automatic time stepping scheme. The numerical model is implemented into an open source in-house scientific finite element code allowing for simulations of applications in various geotechnical areas.

Current research into CO2 capture and storage is dominated by improving the CO2 storage capacity. In this context, risk related to CO2 leakage is an important issue which may cause environmental problems, particularly when freshwater resources nearby are intruded by the CO2 plume. In this work, the leakage into a multi-layered fractured saline aquifer is modelled with a numerical model regarding its pressure build-up process. The investigation is performed with the non-isothermal compositional fluid flow module implemented by authors in the OpenGeoSys (OGS) software for geotechnical applications.