Geoscientific Information Systems Research Articles

Impact of heated basements on the performance of borehole GHEs

Increasing urban development is leading to a growing demand for subsurface utilisation. As more infrastructure is built into the subsurface, heat from tunnels, sewers, and basements, among others, alter the thermal state of the ground, acting as sources and sinks of heat, leading to a net-increase of underground temperatures, a phenomenon known as the Subsurface Urban Heat Island (SUHI) [7-8]. This additional heat can have impacts on, for example, health and maintenance of underground structures, increased ventilation costs for underground spaces, and quality and quantity of groundwater flow [1,2]. However, this additional heat in the subsurface can also be harvested by ground-source heat pump (GSHP) systems to provide heating to buildings [3-6], operating more efficiently due to the higher ground temperatures and reducing these temperatures through operation, thus mitigating the risks and impacts of SUHI.
 This work demonstrates how heated basements can contribute to the operation of GSHP systems to provide heating. The area of Downing College, located in central Cambridge, UK, is used as a case study site, investigating how much of the college’s heating demand a number of geothermal boreholes could provide, when the heat from the building basements is taken into account and when it is not. Measured gas consumption data from the college are used to estimate the heat demand. The geology of the site is obtained by importing historical borehole records for the wider Cambridge area into the British Geological Survey (BGS) Groundhog® Desktop Geoscientific Information System and constraining the domain using BGS generated superficial deposit and bedrock geology maps, thus producing a 3D lithological profile for the region*, while the hydrological conditions were obtained using measured water level time-series data, from water wells in the area, curtesy of the Environment Agency. A total of 88 boreholes are considered, placed symmetrically in the college courtyard, between the main buildings. Typical single U-loop borehole configurations are used with pipes of 32 mm outer diameter. Acknowledging that the effect of heated basements is greater in shallower regions of the subsurface, two typical borehole length values are considered: 50 m, providing about 40% of the required heating load, and 100 m, providing 100%. The operation is simulated over 50 years, using a full 3D numerical model coupling heat transfer, groundwater flow, and pipe flow governing equations, created in COMSOL Multiphysics®. The temperature of the heated basements is assumed to be maintained at 18 °C throughout the simulation. During the first 10 years, the GHEs are not operating, to allow heat accumulation in the ground to occur from the heated basements, following which, 40 years of operating GHEs are simulated.
 The results of the simulations suggest that an increase in performance occurs when heated basements are present. For all scenarios, the fluid temperatures keep decreasing over time, as the ground temperature around the boreholes keeps decreasing, making it more difficult to extract heat. Over the 50 years of simulation, the fluid temperature reaches a minimum of -3.20 °C and -2.13 °C for the 50 m GHEs, and 4.52 °C and 3.88 °C for 100 m GHEs, in both cases the first value being the simulation with heated basements and the second without. The COP values over time are presented in Figure 1-right, showing the difference in COP between the cases with and without heated basements increasing over time for both 50 m and 100 m GHEs, for the former at a higher rate.
 This increase corresponds to the increase in the average fluid temperature between the cases with and without heated basements, also shown in the figure, and reaches a maximum difference of about 0.08 for the 50 m GHEs and 0.05 for the 100 m GHEs, corresponding to a fluid temperature difference of about 1.10 °C and 0.65 °C, respectively. These figures correspond to a reduction in operating costs (assuming an electricity rate of £0.34 per kWh) of £17,352 for 50 m GHEs and £18,197 for 100 m GHEs. While for this case these values are relatively small considering 40 years of operation, the fluid temperature difference suggests that more energy can be extracted by the GHE borheoles when heated basements are present, especially for shorter boreholes, and thus potential savings could be obtained by reducing the number of GHEs.

Finding common ground: identifying shallow geothermal potential for the city of Cambridge, UK

Urban expansion and extensive anthropogenic utilisation of the subsurface can lead to thermal changes in the ground, as structures such as basements, sewage systems, and tunnels reject or absorb heat to/from the ground. This phenomenon, known as Subsurface Urban Heat Island, has been widely documented and studied in recent years [1,7]. Investigations have shown that significant soil and groundwater temperature anomalies can be caused, with local hotspots and temperature differences up to 20 °C [6]. These ground temperature anomalies can affect, for example, ground- and drinking water quality, ecosystem biodiversity, and geothermal energy utilisation, with the latter being the focus of this work.
 The city of Cambridge, UK, shown in Figure 1-left, is adopted as a case study site, and a novel scalable large-scale subsurface modelling methodology [4] is used to obtain an understanding of the ground thermal state, accounting for natural and anthropogenic influences. The geology for the region is obtained by importing historical borehole records for the wider Cambridge area into the British Geological Survey (BGS) Groundhog® Desktop Geoscientific Information System and constraining the lithologies using BGS generated superficial deposit and bedrock geology maps, producing a 3D lithological profile. Water table readings from borehole wells supplied by the Environment Agency are used to create hydraulic head and water table maps for the region. Hydraulic and thermal properties for the materials in the domain were obtained from available literature* [2]. The main anthropogenic features are basements, assumed to be heated at 18 °C, and sewers, assumed linked with building density and at 15 °C. Following the methodology, the domain is separated into 1096 blocks, each 200m by 200 m laterally and 100 m in depth, clustered into 10 archetypes. Each archetype comprises a set of features resulting in a ground thermal state common across all blocks within an archetype [4].
 Having thus obtained the spatially varying ground temperature, the performance of typical shallow geothermal systems throughout the domain is assessed, initially investigating the theoretical geothermal potential. Figure 1-middle, shows the amount of heating power a typical 100 m double U-loop borehole can supply, providing a constant ground load from 1st of October to 31st May over a 50-year operation period. The power is computed using the Finite Line Source model and g-functions [5], setting a lower limit of -2 °C for the ground loop circulating fluid temperature. The results show that hydro-geological features and anthropogenic thermal influences in the region can result in spatial variation of geothermal potential of up to 0.3 kW, or about 1746 kWh per year. A sensitivity analysis indicates that no single feature dominates in the contribution to the magnitude of geothermal potential, suggesting that both natural and anthropogenic sources are important influences on how much energy the ground can provide.
 Extending the analysis by incorporating estimated residential heating demand data [3], Figure 1-right shows the percentage of residential demand that can be fulfilled using geothermal boreholes, assuming these are drilled in suitable parking and non-major road areas for each block, at a minimum spacing of 6 m to avoid thermal interference. The calculations use g-functions to compute how much of the estimated heating demand a single borehole can supply, using half-hour demand distributions for 50 years (repeated annually), and multiplied by the estimated number of boreholes in each block to determine the total geothermal energy that can be supplied. For a large portion of the modelled domain, the entirety of the residential heat demand is expected to be feasibly fulfilled using shallow geothermal energy. Certain areas, mostly agricultural and green spaces with no to low demand, contain no suitable borehole drilling locations, i.e., parking or road areas (a conservative assumption adopted in this study), resulting in no energy being supplied geothermally (light gray). Average demand supplied within the remaining region is 91%, with a standard deviation of 21%.
 As the world urgently seeks to transition to a more sustainable energy infrastructure, utilising different clean energy technologies in a more extensive and organised way becomes increasingly necessary. Geothermal energy technologies can be particularly suited for coordinated large-scale utilisation, due to the significant capital costs and the continuous nature of the ground, acting as a shared resource for large communities. This work briefly demonstrates the capacity that geothermal technologies have to fulfil a significant portion of the residential heat demand at large scales, using the city of Cambridge as an example, and that organisations or governments can take advantage of the potential that exists in finding common ground.

Spatial Variation of Silt and Clay Sediment Deposit in Bhaktapur City

3D geological subsurface model of the Bhaktapur City is prepared using RockWork2016, which is based on 3-D Geo-scientific information system (3-D GSIS). The main aim of this study is to interpret the geological conditions of Bhaktapur city, providing subsurface geological database and its relevance to 2015 Gorkha earthquake damages. For this, the borehole data are collected from different sources and digitized in the RockWork2016 program for the generation of the 3-D attributed subsurface model. For the stratigraphy divisions of the soil, the unified soil classification system is used. From the interpretation of the developed attributed model, it is found that the central part or the core area of the Bhaktapur city has a deeper depth of the soft sediment-silt and clay rather than other surrounding parts of the city. This indicates the possibility of local soil amplification in the central part of the study area. The spatial variation of the subsurface sediment deposit is then co-relate with damage scenario caused by 2015 Gorkha earthquake.

Geotechnical characterization and seismic response of shallow geological formations in downtown Lisbon

<p> </p><p>The geological and geotechnical characterization of shallow formations is one of the main steps in performing a microzonation study. This paper presents an example of the usefulness of the information compiled in a geological and geotechnical database for the estimation of the seismic response of the shallower formations of the Lisbon downtown area of Baixa. The geotechnical characterization of this area was performed based on the analysis of Standard Penetration Test (SPT) data compiled in the geological and geotechnical database. This database, connected to a geoscientific information system (CGIS), allows, also, the definition of 2D geological profiles used for estimating the thickness of the shallower layers. The shear-wave velocities (V<span><sub>S </sub></span>) for each layer were estimated from empirical correlations using mean SPT values computed from the statistical evaluation of the compiled data. These V<span><sub>S</sub></span> values were further calibrated with ambient vibration recording analysis. The seismic response of Baixa’s superficial deposits was estimated by applying a 1D equivalent linear method to a set of soil profiles, regularly distributed across the area, and using synthetic accelerograms to simulate input motions associated with probable earthquake occurrences in Lisbon. The results are presented in terms of maps of predominant frequencies, with the corresponding amplification level, as well as spectral amplification factors for 1 Hz and 2.5 Hz. The results show that the fundamental frequency of the Baixa area is between 1.2 Hz and 2 Hz, for the whole central valley, reaching 3 Hz near the edges where anthroprogenic and alluvial deposits have less expression. Amplification factors up to 5 were obtained. These results were achieved regardless of the considered input motion. The similarity of the obtained fundamental frequency with the natural frequency of Baixa’s old building stock increases the probability of resonance effects in future earthquakes.</p><p><span style="font-size: medium;"><br /></span></p>

Spatial Analysis Techniques as Successful Mineral-Potential Mapping Tools for Orogenic Gold Deposits in the Northern Fennoscandian Shield, Finland

Geoscientific Information Systems (GIS) provide tools to quantitatively analyze and integrate spatially referenced information from geological, geophysical, and geochemical surveys for decision-making processes. Excellent coverage of well-documented, precise and good quality data enables testing of variable exploration models in an efficient and cost effective way with GIS tools. Digital geoscientific data from the Geological Survey of Finland (GTK) are being used widely as spatial evidence in exploration targeting, that is ranking areas based on their exploration importance. In the last few years, spatial analysis techniques including weights-of-evidence, logistic regression, and fuzzy logic, have been increasingly used in GTK’s mineral exploration and geological mapping projects. Special emphasis has been put into the exploration for gold because of the excellent data coverage within the prospective volcanic belts and because of the increased activity in gold exploration in Finland during recent years. In this paper, we describe some successful case histories of using the weights-of-evidence method for the Au-potential mapping. These projects have shown that, by using spatial modeling techniques, exploration targets can be generated by quantitatively analyzing extensive amounts of data from various sources and to rank these target areas based on their exploration potential.

Challenges and trends for geological modelling and visualisation

The successful execution of both large and complex construction projects and environmental and natural hazard assessments requires a precise definition of subsurface conditions. Over the past two decades, a series of sophisticated 3-D modelling technologies—collectively identified as geoscientific information systems, or GSIS—have been developed to address this subsurface characterisation need. Existing commercial systems reflect their historical origins. The modelling and visualisation process remains technically challenging. Rapid development of computer hardware and software, modern data base design concepts and expanded information transmission capabilities across the Internet are encouraging the greater use of GSIS technologies as they become cheaper and easier to use and integrate within corporate decision-support systems. The integration of GSIS with broader information management systems is not common, but limited initial experiences suggest that large benefits are likely to result.

Death valley regional ground-water flow model calibration using optimal parameter estimation methods and geoscientific information systems

A regional-scale, steady-state, saturated-zone ground-water flow model was constructed to evaluate potential regional ground-water flow in the vicinity of Yucca Mountain, Nevada. The model was limited to three layers in an effort to evaluate the characteristics governing large-scale subsurface flow. Geoscientific information systems (GSIS) were used to characterize the complex surface and subsurface hydrogeologic conditions of the area, and this characterization was used to construct likely conceptual models of the flow system. Subsurface properties in this system vary dramatically, producing high contrasts and abrupt contacts. This characteristic, combined with the large scale of the model, make zonation the logical choice for representing the hydraulic-conductivity distribution. Different conceptual models were evaluated using sensitivity analysis and were tested by using nonlinear regression to determine parameter values that are optimal, in that they provide the best match between the measured and simulated heads and flows. The different conceptual models were judged based both on the fit achieved to measured heads and spring flows, and the plausibility of the optimal parameter values. One of the conceptual models considered appears to represent the system most realistically. Any apparent model error is probably caused by the coarse vertical and horizontal discretization.

The application of Diamond Exploration Geoscientific Information System (DEGIS) technology for integrated diamond exploration in the north-central United States of America

Discovery of diamondiferous kimberlite in northwestern Canada, and occurrences of similar intrusions and alluvial diamonds elsewhere, suggest North America is fertile ground for economic primary diamond deposits. Using a Diamond Exploration Geoscientific Information System (DEGIS) to develop an exploration model, we identified four areas of permissive terrain in the northcentral United States: Wisconsin-Upper Peninsula of Michigan, southeastern Wyoming, North Dakota-Minnesota-Ontario, and northwestern Iowa. Permissive areas feature lithosphere that is > 1.6 billion years old and > 150 km thick; and prospective zones within this terrain contain point and linear features that are associated with kimberlite and lamproite emplacement.

The DASDBS project: objectives, experiences, and future prospects

A retrospective of the Darmstadt database system project, also known as DASDBS, is presented. The project is aimed at providing data management support for advanced applications, such as geo-scientific information systems and office automation. Similar to the dichotomy of RSS and RDS in System R, a layered architectural approach was pursued: a storage management kernel serves as the lowest common denominator of the requirements of the various applications classes, and a family of application-oriented front-ends provides semantically richer functions on top of the kernel. The lessons that were learned from building the DASDBS system are discussed. Particular emphasis is placed on the following issues: the role of nested relations, the experiences with using object buffers for coupling the system with the programming-language environment and the learning process in implementing multilevel transactions. >

Digital geoscientific maps: A priority program of the German Society for the Advancement of Scientific Research

In October 1984, the German Society for the Advancement of Scientific Research (DFG) began a 5-year Priority Program to develop a new general concept for computer-assisted field work and construction, production, and evaluation of geoscientific maps with contents either from a single geodiscipline or from various disciplines, as a part of a future geoscientific information system.