This paper proposes a method to assess the potential for thermal use of groundwater and its integration in spatial energy planning. The procedure can be adapted to local regulatory and operational ...limits, thus estimating legally and technically achievable flow rates and subsequently, the thermal power that can be exchanged with the aquifer through a well doublet.
The constraints applied to flow rates are i) a drawdown threshold in the extraction well, ii) a limit for the groundwater rise in the injection well and iii) a threshold to avoid the hydraulic breakthrough between the two wells. For the spatial assessment, the hydraulic influence on neighbouring well doublets is simulated with the maximum flow rates before the hydraulic breakthrough occurs. The Thermal Aquifer Potential (TAP) method combines mathematical relations derived through non-linear regression analysis using results from numerical parameter studies. A demonstration of the TAP method is provided with the potential assessment in Munich, Germany. The results are compared with monitoring data from existing open-loop systems, which prove that conservative peak extraction estimates are achieved.
•Integration of thermal groundwater use in spatial energy planning.•Estimation of technically achievable flow rates for well doublets.•Mathematical relations based on numerical modelling results.•Method application in Munich with detailed hydrogeological data.•Evaluation with monitoring data from existing open-loop systems.
•A critical review on the energy pile technologies from the life-cycle perspective was conducted.•Low-carbon considerations and optimization measures of energy piles are systematically ...summarized.•Potential challenges for decarbonizing energy piles were analyzed considering the environmental impact assessments.•Systematic theory and methodology for optimal decarbonization of energy piles were proposed.
Energy piles, a technology integrating the heat exchange component within building pile foundations for shallow geothermal energy utilization, have proven economically efficient. They outperform conventional ground source heat pumps by mitigating additional borehole costs and space requirements. This paper systematically examines low-carbon considerations and optimization measures throughout the planning, design, construction, and operation stages of energy piles, considering the entire lifecycle. Furthermore, this paper discusses potential challenges associated with decarbonizing energy piles, offering solutions based on case studies and environmental impact assessments. Through a comprehensive critical review and analysis of existing knowledge, this paper presents a systematic theory and methodology for optimal decarbonization of energy piles, serving as a valuable resource for building practitioners and researchers in this field. The findings not only contribute to a solid theoretical foundation but also provide technical support for the advancement and application of energy pile systems.
Anthropogenic infrastructures in the shallow subsurface, such as heated basements, tunnels or shallow geothermal systems, are known to increase ground temperatures, particularly in urban areas. ...Numerical modelling helps inform on the extent of thermal influence of such structures, and its potential uses. Realistic modelling of the subsurface is often computationally costly and requires large amounts of data which is often not readily available, necessitating the use of modelling simplifications. This work presents a case-study on the city centre of Cardiff, UK, for which high resolution data is available, and compares modelling results when three key modelling components (namely ground elevation, hydraulic gradient distribution and basement geometry) are implemented either ‘realistically’, i.e. with high resolution data, or ‘simplified’, utilising commonly accepted modelling assumptions. Results are presented at a point (local) scale and at a domain (aggregate) scale to investigate the impacts such simplifications have on model outputs for different purposes. Comparison to measured data at individual locations shows that the accuracy of temperature outputs from numerical models is largely insensitive to simplification of the hydraulic gradient distribution implemented, while changes in basement geometry affect accuracy of the mean temperature predicted at a point by as much as 3.5 °C. At the domain scale, ground temperatures within the first 20 m show a notable increase (approximately 1 °C volume-averaged and 0.5 °C surface-averaged), while the average heat flux over the domain is about 0.06 W/m2 at 20 m depth. These increased temperatures result in beneficial conditions for shallow geothermal utilisation, producing drilling cost savings of around £1700 per typical household system or about 9% increase in thermal energy potential. Simplifications of basement geometry and (to a lesser degree) the hydraulics can result in an overestimation of these temperatures and therefore over-predict geothermal potential, while the elevation simplification showed little impact.
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•Heated basements shown to increase volumetric ground temperature by up to 1.1 °C•Locally, modelling simplifications are more appropriate within groundwater flow.•At global scale, modelling simplifications somewhat overestimate ground temperature.•Simplifying heat source (basement) geometries shows greatest impact on temperature.•In this case study, heated basements increase shallow geothermal potential by 9–11%.
•Three novel evaluation indexes were defined to evaluate the thermal performance.•Increasing heating load alone isn’t the best way improving the thermal performance.•There is a complex interaction in ...the heating load, flow rate, and operation mode.•The optimized SVR model can predict the thermal performance satisfactorily.
Energy walls (i.e. wall heat exchangers) exhibit more complex thermal performance than do energy piles and borehole heat exchangers in ground source heat pump systems, due to their individual geometry. This study conducted field tests of energy wall thermal performance to analyze the influence and interaction of the pipe burial depth, flow rate, heating load, and operation mode. To evaluate the energy wall thermal performance in multiple dimensions, three novel evaluation indices (energy utilization ratio, thermal saturation, and effectiveness) were defined. A thermal performance SVR prediction model of an energy wall was established based on 227 field-measured samples. The heat exchange power, energy utilization ratio, and effectiveness of the ground side pipe are approximately 15%, 8% and 64% greater than those of the excavated side pipe, respectively. Considering the interaction between the flow rate and heating load, blindly increasing the heating load is not the most effective way to improve the thermal performance. The influences of heating loads and operation modes on heat exchange power differs from that on the energy utility ratio and both side’s thermal saturations, indicating that there is a complex interaction between the heating loads and operation modes. The cross-verification and prediction results show that the optimized thermal performance of the SVR model exhibited satisfactory generalizability and prediction performance.
In this study, a laboratory-scale prototype of a borehole field has been designed and built to assess various innovative grouting products in a fully controlled environment. Three novel grout ...formulations are developed and evaluated: enhanced grout, a mixture of enhanced grout and microencapsulated phase change material, and a mixture of enhanced grout and shape stabilized phase change material. The objective is to evaluate the enhancement in their thermal properties (i.e., thermal conductivity and thermal energy storage capacity) compared to those using a commercial reference grout. Besides, three-dimensional numerical modeling is performed to provide a better understanding of the heat transfer and phase transition inside and outside the grout columns and to study the capability of the developed grouts to be used in a borehole heat exchanger or as borehole thermal energy storage system. To the best of the authors' knowledge, there have been just a few numerical studies on using phase change materials inside borehole heat exchangers to assess thermal energy storage applications. The experimental and numerical results showed much higher efficiency of the grout developed with a high thermal conductivity than the reference grout in terms of heat transfer in both the grout column and the surrounding sand. Furthermore, the results indicated the noticeable influence of the microencapsulated phase change material's presence in the grout formulation in terms of heat absorption/storage during the phase transition (from solid to liquid). However, it is concluded that reengineering shape stabilized phase change material should be conducted to make it more appropriate for thermal energy storage applications.
•A laboratory-scale prototype has been designed to test innovative grouting products.•Three novel grouts are tested: enhanced grout, addition of microencapsulated PCMs, and addition of shape stabilized PCMs.•The aim is to study the improvement of thermal conductivity and thermal energy storage.•Thermally enhanced grout indicated significant increase in the thermal conductivity.•Adding the microencapsulated PCMs improves the heat storage capacity remarkably.
Geothermal pavements can be used with ground-source heat pump systems to sustainably provide energy for heating and cooling by incorporating ground heat exchanger elements underneath pavement ...surfaces. This work investigates the suitability of geothermal pavements at scale, adopting the city of Cardiff, UK, as a case-study. A two-scale modelling framework, combining detailed small-scale with holistic large-scale approaches, is presented, incorporating the accuracy of the former with the continuity of the latter. The results show that between 184 kWh and 345 kWh of thermal energy per metre length of pavement can be supplied annually, depending on soil profile. Moreover, geothermal operation can reduce anthropogenic heat flux into the ground from heated basements, and its associated negative impacts, by about 390 MWh/year. A city-scale analysis using population-consistent geographic areas called LSOAs, estimates that geothermal pavements can supply about 23% of the entire city residential heat demand, or up to 75% with heat sharing between LSOAs. The suitability of geothermal pavements for larger LSOAs is highlighted, supplying up to 100% of the annual domestic heat demand. Investigating the carbon emissions of heating and cooling technologies shows potential reductions of up to 75% when replacing gas boilers and resistance heating with geothermal pavement systems.
•Two-scale modelling is used to assess city-scale geothermal pavement potential.•Depending on ground conditions, 184–345 kWh annually/m road of heat can be provided.•Geothermal pavements can reduce anthropogenic heat flux into the ground by ∼390 MWh/a.•In low population density areas 100% residential demand can be fulfilled, overall 23%.•Replacing traditional systems can reduce carbon emission by ∼75%.
•A mathematical model of medium-shallow array borehole heat exchangers was built.•Explored the influencing factors on heat transfer performance of medium-shallow BHEs.•An operation optimization ...strategy for circulating fluid was developed.•The variable flow strategy of circulating fluid affects the performance of heat pump.
Medium-shallow array borehole heat exchangers (MSABHEs) exhibit high heat transfer capacity and low initial investments. However, limited research has been conducted on utilizing medium-shallow geothermal energy utilization for heating and cooling. In this study, a heat transfer model for MSABHEs was established. Second, the suitability of the heat transfer model was validated using experimental data. Subsequently, the model was used to analyze the impacts of the borehole spacing, terrestrial heat flow, circulating fluid flow rate, and ground depth on heat transfer in MSABHEs. Finally, an optimization strategy for the circulating fluid was proposed based on dynamic building loads, and the impacts of various circulating liquid control strategies on the heat pump performance were compared. The results indicated that the heat transfer capacity of the MSABHEs increased with increasing borehole spacing. When the spacing was greater than 8 m, thermal interference between the boreholes could be ignored. Under the condition of imbalanced cooling and heating loads, the variable flow strategy could increase the heating coefficient of performance (COP) and cooling COP of the heat pump by approximately 11.12 % and 14.28 %, respectively. Through this control method, the power consumption of the water pump could be reduced from 15840 kW to 8527 kW. These findings could provide a theoretical basis and technical guidance for MSABHE applications.
This study proposes a liquid desiccant dehumidification system combined with shallow geothermal energy. Calcium chloride solution is adopted as a desiccant that is sprayed directly on outdoor air for ...dehumidification purposes. Shallow geothermal energy is a clean renewable energy that is located beneath the ground surface approximately 3–50 m deep. In this study, the shallow geothermal energy water is utilized as a substitute for chilled water or cooling water. Shallow geothermal energy water, at about 20–22 °C, could precool outdoor air and cool the desiccant solution. Precooling outdoor air before it enters the dehumidifier can remove a sensible cooling load in advance and increase the performance of the dehumidifier. Moreover, the lower temperature solution is beneficial for enhancing sensible, latent, and total heat transfer rates. Based on the calculated results, under the same operating conditions, compared to the condensation system and the traditional liquid desiccant dehumidification system, the proposed system saves 86% and 82%, respectively, on power consumption. Result shows that a liquid desiccant dehumidification system integrated with shallow geothermal energy is an effective approach to enhance dehumidification performance and cooling capacity.
In this study, a cooling system with shallow-geothermal energy is experimentally investigated to mitigate the photovoltaic panel conversion efficiency decline problem, and a mathematical model is ...built for predicting the system performance. This cooling system cools the panel by spraying water onto the reverse of the panel, and returns the water to the tank. To enhance the cooling capacity, the recycled water is collected in a U-shaped borehole heat exchanger (UBHE), which is installed in an existing well, and the water exchanges heat with shallow-geothermal energy. Finally, the panel is again sprayed with water to cool it. The experiments are comprised of three stages: The first involved the panel operating without cooling system. The second involved the panel operating with a cooling system but without a UBHE. The third is the cooling system operating with a UBHE. The experimental results and the mathematical models show the same trend: The cooling system can improve the panel conversion efficiency; moreover, as the temperatures and the number of panels increase, the benefit becomes obvious. For a plant factory powered by panels, for example, this cooling system can improve the efficiency by 14.3%, and its equipment costs recovered in 8.7 years with this system.
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•A cooling system, combined with shallow geothermal energy, is applied to a photovoltaic panel system for the mitigation of the efficiency decline caused by high temperatures.•The U-shaped borehole heat exchanger can maintain the cooling capacity of the cooling system while reducing energy consumption.•A mathematical model is developed for estimating a photovoltaic panel's temperature and conversion efficiency under different conditions.
One promising way to improve the efficiency of borehole heat exchangers (BHEs) in shallow geothermal applications is to enhance the thermal properties of the materials involved in its construction. ...Early attempts, such as using metal tubes in the 1980s or the utilization of thin–foil hoses, did not succeed in being adopted by the market for diverse reasons (cost, corrosion, fragility, etc…). In parallel, the optimization of pipe size, the use of double-U-tubes, thermally enhanced grout, etc. were able to bring the measure for the BHE efficiency, the borehole thermal resistance, from 0.20 to 0.15 K/(Wm) down to 0.08–0.06 K/(Wm) in the best solutions today. A further improvement cannot be expected without development of new, dedicated materials, combining the versatility of plastic like PE with an increased thermal conductivity that matches the respective properties of the rock and soil. This goal was included in the Strategic Research and Innovation Agenda of the European Technology Platform on Renewable Heating and Cooling in 2013.
Within an EU supported project, both BHE pipes and grouting materials have been produced prototypically in small amounts, suitable for the first tests in the intended environment.
The present work explains the research pathways envisaged and the resulting sensitivity analysis to highlight the influence of some of the most critical parameters that affect the overall performance of a GSHP system. The results have allowed guiding the real development of more efficient new advanced materials for different scenarios representative of different European regions. Finally the developed materials and their properties are discussed, including a comparative assessment about their compliance with reference material properties as currently seen in the BHE market.
•A vast parameter study for the development of new geothermal materials.•The objective is to obtain the best specifications for pipe and grout materials.•Representative scenarios of all simulations carried out are presented.•Assessment of combined enhancement of pipe thermal conductivity and grouting.•The implementation of the enhanced products could produce a reduction of up to 22%.
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