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A full-scale mock-up geothermal bridge was built in Texas, USA, to evaluate the field performance of a novel external geothermal bridge de-icing system. The geothermal bridge system comprises a single U-loop ground heat exchanger (GHE) 131 m deep, a geothermal heat pump, four circulation pumps, and hydronic heating loops attached to the bridge deck. A comprehensive monitoring system was implemented to monitor the spatial ground temperature response. The geothermal bridge system was operated and monitored for solar collector and bridge de-icing operations totaling 99 days between August 2019 and April 2020. An average heat injection of 5.7 W/m was observed during the solar collector operation. Based on the defined control volume, approximately 48.9–380.8 kWh of energy, corresponding to 3.7%–28.5% of the total injected energy, was available at the end of the solar–collector operation. Moreover, test results showed that 31.7%–39.4% of stored thermal energy was preserved for utilization in the first winter de-icing test. The radius of the influence zone of the GHE operation was found to be 3.45 m. The outcome of the field experimental studies and further data collection performed over a year of operations showed that the heat injection into the soil by bridge solar collector was 54% more effective than heat extraction from the ground during the several de-icing tests performed from 2019 to 2020. [ABSTRACT FROM AUTHOR]

Geothermal systems face adoption challenges due to their high initial investment cost. Accurate cost analyses and a more precise understanding of updated prices could assist geothermal industry projects in obtaining investment financing and better money management with the right equipment. As the cost of geothermal installations can vary widely depending on case and location, it seems essential to clarify the factors and parameters that determine the cost of the system. These include the type of loop system, the ground conditions, the type of heat pump, the system size, and the geographical location. The scope of this study is to compare the operation of various types of ground heat exchangers (GHEs) present in a Ground Source Heat Pump (GSHP) system installed in the coastal area of the Mediterranean climate zone of Cyprus. The highlight of this work is that it presents real installation cost data as well as recorded total energy contributed by the GHEs to the GSHP system of a HP cooling and heating capacities of 101 kW and 117 kW, respectively. The input contribution from the GHEs to the HP is 85,650 kWh (308,340 MJ) in summer and 25,880 kWh (93,168 MJ) in winter. It is shown that, among the three groups of GHEs investigated, the open-well GHE complex has the lowest cost per kWh ratio (0.32 EUR/kWh), followed by the vertical GHE complex (1.05 EUR/kWh), and lastly by the helical coil GHE (2.77 EUR/kWh). This clearly suggests that when underground water is available, the open-well GHE is much more favorable than other GHE types. [ABSTRACT FROM AUTHOR]

Abstract This study introduces an experimental investigation of a novel direct trend evaporative cooler based on a ground-air heat exchanger (GAHE) using porous clay vessels as an evaporation media under a variety of operational conditions, including air flow rate, inlet air temperature, temperature of inlet water, and in air humidity. The evaluation of the GAHE performance was based on the air-cooling effect, wet-bulb and dew-point efficiencies, energy efficiency ratio, water evaporation rate, specific water evaporation, specific cooling capacity, specific total cost, and CO2 emission rate. The influences of dry-bulb temperature, the incoming air's relative humidity (RH), and six air flow rates ranging from 11 to 25 L/s on the performance are investigated and discussed. Results indicated that increasing the air flow rate leads to an increase in the cooling capacity. Energy efficiency ratio (EER) reaches the highest value of about 25.5 recorded at 3:00 PM with air flow rate = 11 L/s. The lowest EER value is approximately 7.2 when the measured inlet and outlet temperatures are the closest at 7:00 PM, with a flow rate of 25 L/s. Increasing the air flow rate from 11 to 17 L/s increased the wet bulb efficiency, and the airflow rate was inversely proportional to wet-bulb efficiency. The maximum and minimum average dew-point efficiencies are 64% and 58% at 17 L/s and 22 L/s respectively. The water evaporation rate increases by 182.1%, increasing the air flow rate from 11 to 25 L/s.

Rising energy prices have increased the popularity of many renewable energy sources including heat pumps. In the case of ground heat pumps research related to the analysis of the operation and selection of ground heat exchangers as a heat source are insufficient. With this in mind, on the operation of the horizontal slinky coil heat exchanger research work has been undertaken. As a research tool, the Computational Fluid Dynamics has been used. To check the adequacy of the CFD model, a validation of the model was carried out using the results of research on a real heat exchanger. Comparison was made: values of ground temperatures, outlet temperatures from the exchanger, and heat flux exchanged by the heat exchanger. In the opinion of the authors, the validation of the CFD model was successful.

A large number of ground-source heat pump (GSHP) systems have been used in residential and commercial buildings throughout the world due to their attractive advantages of high energy and environmental performances. In particular, GSHPs constitute a proven renewable energy technology for space heating and cooling. This paper provides a detailed literature review of the primary aspects of GSHP systems. These include the technological characteristics of HPs and the main types and variations in GSHPs, along with their environmental impact. Other aspects addressed are the integration of GSHPs with other systems, as well as their optimal design and control and energy analysis. The important aspect of the system's performance is also dealt with through case studies and also the barriers hindering the further adoption of GSHPs in buildings. Two important challenges for the adoption of GSHPs is their cost and environmental efficiency. Studies have shown that GSHPs can reach a >>24% lower environmental impact than air-source HPs, while today's technology can allow for a payback period for installing a GSHP of <<5 years. Finally, based on the above review, the future challenges and prospects for the successful uptake of GSHPs is discussed. It seems that through the right steps, the wide adoption of GSHPs as an important form of 'implemented' renewable energy system can become a reality. [ABSTRACT FROM AUTHOR]

Kuwait stands as one of the hottest locations globally, experiencing scorching temperatures that can soar to 50 °C during the summer months. Conversely, in the winter months of December and January, temperatures may plummet to less than 10 °C. Maintaining a comfortable temperature indoors necessitates a substantial amount of energy, particularly during the scorching summer seasons. In Kuwait, most of the electrical energy required for functions such as air conditioning and lighting is derived from fossil fuel resources, contributing to escalating air pollution and global warming. To reduce dependence on conventional energy sources for heating and cooling, this article presents a case study to explore the potential of using geothermal energy for space heating and cooling in Kuwait. The case study involves utilizing a geothermal heat pump (water-sourced heat pump) in conjunction with a vertical-borehole ground heat exchanger (VBGHE). The mentioned system is deployed to regulate the climate in a six-floor apartment block comprising a small two-bedroom apartment on each level, each with a total floor area of 57 m2. Two geothermal heat pumps, each with a cooling capacity of 2.58 kW and a heating capacity of 2.90 kW, connected to two vertical-borehole heat exchangers, were deployed for each apartment to maintain temperatures at 22 °C in winter and 26 °C in summer. The findings indicate that the estimated annual energy loads for cooling and heating for the apartment block are 42,758 kWh and 113 kWh, respectively. The corresponding electrical energy consumption amounted to 9294 kWh for space cooling and 113 kWh for space heating. The observed peak cooling load was approximately 9300 kJ/h (2.58 kW) per apartment, resulting in a power density of 45 W/m2. Moreover, the HP system achieved a 22% reduction in annual electric energy consumption compared to conventional air conditioning systems. This reduction in electric energy usage led to an annual CO2 reduction of 6.6 kg/m2. [ABSTRACT FROM AUTHOR]

This paper investigates the total environmental impacts of a thermal caisson (TC) system by implementing a life cycle assessment methodology. The total environmental impacts consider the comprehensive effect on the environment across two life cycle stages: manufacturing and operation. A comparison between the TC results and two different HVAC systems, including air-conditioning/furnace and conventional ground-source heat pump (GSHP) systems, was made by adopting the ReCiPe 2016 methodology. This study reveals that the operation phase is the predominant contributor to environmental impacts across systems, mainly due to its extended duration. Specifically, the operational impacts of GSHPs are substantial, accounting for approximately 87% of total environmental impacts. A TC GSHP system demonstrates a notable environmental advantage, achieving a 79% reduction in total environmental impact when compared to traditional AC/furnace systems. This represents a 21% improvement over conventional GSHP systems. Despite this substantial reduction in total environmental impact, the TC GSHP system shows an almost 5% increase in the resource availability damage category relative to the conventional GSHP, which is attributed to its higher material consumption. These results highlight the TC GSHP system's superior efficiency in reducing environmental impacts and its potential as a more sustainable alternative in residential heating and cooling applications. [ABSTRACT FROM AUTHOR]

Ground heat exchanger (GHE) is the most crucial element of a ground source heat pump (GSHP) system for building cooling and heating by the utilization of geothermal energy. Therefore, intending to enhance the performance of GHE, the present study conducts a computational investigation of the thermal performance of modified spiral tube vertical GHEs. Several modifications of uniform-pitched spiral GHE are made to increase its thermal performance. Some modifications are introduced as variable-pitched spiral tube GHE where spiral inlet pipes are densified in the lower part of GHEs by reducing pitch distance. Conversely, in some modifications, the position of the outlet straight pipe is changed. Water is considered as the working fluid and the inlet temperature of the water is maintained fixed at 300.15 K. After extensive analysis, it is evident that, when the outlet pipe is placed outside of the spiral coil, there is a 7.67 % enhancement in the thermal performance than a traditional uniform-pitched spiral tube GHE. However, modifications like variable-pitched spiral tube GHEs are not significant to improve the thermal performance due to the quick saturation of the ground soil temperature around the GHE pipes. To have a balance between heat transfer rate and pressure drop, thermal performance capability (TPC) and coefficient of performance improvement (COPimprvt) criterion were evaluated and it is found that the uniform-pitched spiral tube GHE along with the outlet pipe at the outside of the spiral provides maximum thermal performance with a maximum TPC value of 1.062 and provides the positive value of COPimprvt criterion. The positive values of COPimprvt indicate that the spiral tube GHEs are energy efficient based on heat transfer and pressure drop. Moreover, spiral GHE with high-density polyethylene (HDPE), concrete pile, and sandy clay outperform the other materials for pipe, backfill, and soil, respectively. Specifically, HDPE pipe, concrete backfill, and sandy clay as soil offer around 7 %, 5 %, and 7.8 % higher thermal performance compared to polyethylene, sand silica, and clay, respectively.

Geothermal systems face adoption challenges due to their high initial investment cost. Accurate cost analyses and a more precise understanding of updated prices could assist geothermal industry projects in obtaining investment financing and better money management with the right equipment. As the cost of geothermal installations can vary widely depending on case and location, it seems essential to clarify the factors and parameters that determine the cost of the system. These include the type of loop system, the ground conditions, the type of heat pump, the system size, and the geographical location. The scope of this study is to compare the operation of various types of ground heat exchangers (GHEs) present in a Ground Source Heat Pump (GSHP) system installed in the coastal area of the Mediterranean climate zone of Cyprus. The highlight of this work is that it presents real installation cost data as well as recorded total energy contributed by the GHEs to the GSHP system of a HP cooling and heating capacities of 101 kW and 117 kW, respectively. The input contribution from the GHEs to the HP is 85,650 kWh (308,340 MJ) in summer and 25,880 kWh (93,168 MJ) in winter. It is shown that, among the three groups of GHEs investigated, the open-well GHE complex has the lowest cost per kWh ratio (0.32 EUR/kWh), followed by the vertical GHE complex (1.05 EUR/kWh), and lastly by the helical coil GHE (2.77 EUR/kWh). This clearly suggests that when underground water is available, the open-well GHE is much more favorable than other GHE types.

Ground heat is a renewable energy source that is less affected by atmospheric temperature and maintains a nearly constant temperature throughout the year. Therefore, it can serve as a heat source for hot water and air conditioning systems, resulting in a significant reduction in carbon dioxide emissions compared to conventional systems. In Japan, the recognition of the use of ground heat is still low, and the prices of ground heat exchangers and geothermal heat pumps tend to be high. In addition, the excavation cost is very high, so it is very important to reduce the construction cost. One cost-saving method is to install a ground heat exchanger in the core material of the earth retaining wall, which has been shown to reduce construction costs by more than 50%. In this study, a numerical program was developed to clarify the performance and characteristics of a ground heat exchanger attached to an H-beam in a “Pre-installation method using the earth retaining wall”. Then, the factors influencing the heat extraction performance of two U-Tube heat exchangers connected in series, four U-Tube heat exchangers connected in series and two W-Tube heat exchangers connected in series were investigated. Firstly, the validity of the calculation program was confirmed by comparing the numerical results with the experimental thermal response results. Secondly, numerical simulations were performed using the calculation program, and the following results were obtained. Under the conditions defined in this study, we found that the rate of heat extraction increases as the flow rate of the heat extraction medium increases in all ground heat exchangers. However, it becomes difficult to increase the heat extraction when the flow of the heat extraction medium reaches a turbulent area. All three models confirmed that the H-beam expanded the area where the formation temperature changes and increased the temperature of the heat extraction medium. This led to an enhanced heat extraction performance of the ground heat exchanger. Finally, we compared the heat extraction performance of several ground heat exchangers using the 'coefficient of heat extraction or rejection'. The results showed that the four U-Tube model had the highest performance, followed by the two W-Tube model, and the two U-Tube model had the lowest performance, although the differences were small.

A large number of ground-source heat pump (GSHP) systems have been used in residential and commercial buildings throughout the world due to their attractive advantages of high energy and environmental performances. In particular, GSHPs constitute a proven renewable energy technology for space heating and cooling. This paper provides a detailed literature review of the primary aspects of GSHP systems. These include the technological characteristics of HPs and the main types and variations in GSHPs, along with their environmental impact. Other aspects addressed are the integration of GSHPs with other systems, as well as their optimal design and control and energy analysis. The important aspect of the system’s performance is also dealt with through case studies and also the barriers hindering the further adoption of GSHPs in buildings. Two important challenges for the adoption of GSHPs is their cost and environmental efficiency. Studies have shown that GSHPs can reach a >>24% lower environmental impact than air-source HPs, while today’s technology can allow for a payback period for installing a GSHP of <

A ground-source heat pump (GSHP) system is a renewable energy technology that effectively reduces greenhouse gas emissions and consequently mitigates the progression of global warming. The thermal efficiency of ground heat exchangers (GHEs) is a critical component in the GSHP system that must be accurately estimated for its long-term operationality. Therefore, in this study, the thermal performance of double-spiral GHEs incorporated within the thermal piles of a zero-energy building in Sapporo, Japan, was investigated using the actual measured data obtained from the site and a novel metric, namely, the coefficient of heat extraction/injection, for a more precise evaluation. Moreover, this study assessed the coefficient of performance (COP) of the GSHP units during various periods of cooling or heating. The temperature of the circulating fluid remained within an ideal operational range over an operational period of 2 years, and the COP calculations indicated a high operational efficiency. The results derived in this study substantially exceeded those of traditional U-tube GHEs, indicating the enhanced efficiency and superior performance of large-diameter thermal piles with augmented thermal capacity. Our findings suggest that GSHP systems with double-spiral-tube GHEs have superior efficiency than conventional GHEs. [ABSTRACT FROM AUTHOR]

The ground‐source heat pump heating and cooling system is currently the most important development and utilization method of shallow geothermal resources, but its key component is the ground heat exchanger system. Herein, a new type of ground heat exchanger, the soil‐cement energy pile, is proposed. The similarity model comparison experiments of the soil‐cement energy piles and the soil energy pile in summer and winter were conducted respectively, and the 3D numerical models of heat transfer of the two kinds of energy piles are established, their related thermal properties are verified. Then the heat transfer calculation methods of the soil‐cement energy pile are presented and validated. The research has shown that the soil‐cement energy pile has good thermodynamic performance, which effectively reduces the largest thermal resistance in the heat transfer system of the energy pile, the thermal resistance of pile body material, and the heat transfer per linear meter of the soil‐cement energy pile is 21.20%–55.60% higher than that of the soil energy pile. The soil‐cement energy pile is of great significance to improve the thermal efficiency of the ground‐source heat pump system and can reduces the overall project cost. [ABSTRACT FROM AUTHOR]

This paper investigates the total environmental impacts of a thermal caisson (TC) system by implementing a life cycle assessment methodology. The total environmental impacts consider the comprehensive effect on the environment across two life cycle stages: manufacturing and operation. A comparison between the TC results and two different HVAC systems, including air-conditioning/furnace and conventional ground-source heat pump (GSHP) systems, was made by adopting the ReCiPe 2016 methodology. This study reveals that the operation phase is the predominant contributor to environmental impacts across systems, mainly due to its extended duration. Specifically, the operational impacts of GSHPs are substantial, accounting for approximately 87% of total environmental impacts. A TC GSHP system demonstrates a notable environmental advantage, achieving a 79% reduction in total environmental impact when compared to traditional AC/furnace systems. This represents a 21% improvement over conventional GSHP systems. Despite this substantial reduction in total environmental impact, the TC GSHP system shows an almost 5% increase in the resource availability damage category relative to the conventional GSHP, which is attributed to its higher material consumption. These results highlight the TC GSHP system’s superior efficiency in reducing environmental impacts and its potential as a more sustainable alternative in residential heating and cooling applications.

As an energy-efficient and low-carbon technology, ground-source heat pumps are promising to contribute to carbon neutrality in the building sector. A crucial component of these systems is the ground heat exchanger, which has been extensively studied through sandbox experiments. These experiments play a vital role in understanding heat transfer characteristics and validating simulation results. In order to facilitate the improvement of ground heat exchangers and the development of ground-source heat-pump systems, this article provides a comprehensive summary of existing sandbox experiments. The borehole sandbox experiments are classified into the single borehole experiment, borehole group experiment, seepage experiment, and multi-layer soil experiment. It was observed that the heat transfer efficiency of a single spiral tube is only 80% compared to that of a double spiral tube. Moving on to energy-pile sandbox experiments, they are further divided into mechanical performance, thermal performance, and thermal-mechanical coupled performance tests. It was revealed that the heat transfer distance of a single U-shaped energy pile in the radial direction is three times greater than in the vertical direction. For the mentioned sandbox experiments, the sandbox design, experiment conduction, testing conditions, and result analyses are summarized. To improve the sandbox experiments, there are still some difficulties in building a similarity experiment, testing the temperatures in a small error, controlling the boundary conditions accurately, and testing the thermophysical properties of soil accurately. Furthermore, the perspectives of sandbox experiments of ground heat exchangers are also proposed. The sandbox experiments under complex environment conditions or with novel composite energy geo-structures or ground heat exchangers with new materials and new technologies would be further investigated. By addressing these aspects, this review aims to provide guidelines for the design, construction, operation, and optimization of sandbox experiments for different ground heat exchangers, ultimately promoting the wider adoption of ground-source heat pumps in achieving carbon neutrality. [ABSTRACT FROM AUTHOR]

Many subarctic communities rely entirely on fossil fuels for their energy needs. Solar-assisted ground-coupled heat pumps (SAGCHP) can be a solution to integrate renewable energy sources into their energy portfolios. However, it is currently unknown how such systems could operate in the context of the high North (cold ground, extreme mismatch between insolation and heating need, electricity from diesel). The objective of the paper is to develop a detailed model of a SAGCHP heating a house in Nunavik (Quebec, Canada) in order to gain a better understanding of its potential and limitations. The solar assistance is provided by PVs. Simulations with and without electric storage (batteries) were run. A complex tradeoff between four different modes of operation was obtained depending on the conditions of the system at each time step. For the test case, results show that the ground experiences a weak long-term thermal depletion partly compensated solar energy, but that a significant portion of the PV power production is preferably used by the compressor or stored in batteries rather than stored in the ground as heat. Over ten years, the SAGCHP system reduced fuel consumption respectively by 38.2% (without a battery) and 59.1% (with a battery). [ABSTRACT FROM AUTHOR]

Heat pumps perform better when coupled with ground as thermal source than with air. In literature, several studies and applications suggest and analyse the use of phase change materials (PCMs) coupled with single or double U-tube vertical borehole heat exchangers (BHEs). Usually, PCMs are mixed with the grouting material during the installation. An alternative solution to vertical BHEs is the use of horizontal ground heat exchangers (HGHEs). The present work investigates the possibility of coupling PCMs with a flat-panel HGHE installed inside a trench 2 m under the ground surface. The study analyses the case in which PCMs are adjacent to the HGHE, taking a cue from alternative coupling technologies which have PCMs added to the backfilling material of the trench where the HGHE is installed. The analysis has been conducted with COMSOL software tool. A simulation model of the system was developed to carry out a parametric analysis. The objective of the simulations is the investigation of the thermal behaviour of the HGHE patent pending coupled with PCMs under cycles of operation which represent how the heat pump could work in GSHP system. The results show the meaningful difference of using the PCM in direct contact with the HGHE. [ABSTRACT FROM AUTHOR]

This study proposes a real-time probabilistic estimation method for determining the thermal properties of backfill used in underground power transmission lines and ground heat exchangers. The thermal properties of backfill, serving as a heat conductor between the heat source and surrounding soil, are crucial design parameters for underground transmission lines and ground heat exchangers because temperature limits their maximum operational output. However, an unpredictable environment and human fieldwork during on-site backfill construction lead to considerable performance uncertainty, requiring in situ thermal property estimation. Furthermore, when transmission lines are installed over long distances, on-site assessments are necessary at multiple locations, making it essential to reduce the experimental time. The proposed estimation method enables real-time monitoring of temporal changes in the estimated probability distribution of the thermal property and quantifies the estimation uncertainty. The proposed method also allows immediate decision-making regarding experiment termination by evaluating real-time convergence by calculating the Jensen-Shannon divergence of sequentially estimated probability distributions. The effectiveness of the proposed method was tested on two backfill materials, demonstrating its ability to determine the estimation convergence by capturing contextual information affecting the estimation uncertainty.

A horizontal ground heat exchanger installation is less expensive than a vertical ground heat exchanger, but more land is required. The system’s required pipe length and land area can be decreased by improving the system. On the other side, adding fins is one strategy to increase heat transfer. In this paper, cylindrical fins are explored in horizontal ground heat exchangers for the first time to improve heat transfer and, the overall efficiency of the ground-source heat pump. These fins were examined by varying parameters such as length, diameter, position, and material. The heat transfer rate changes with and without fins were also investigated as soil properties changed. The heat transfer simulations in cooling mode for a 1D-3D model using COMSOL Multiphysics revealed that changing the fin diameter directly affects the outlet temperature and, the non-isothermal pipe flow (niofl) is used for the pipe. There is minimal difference between improving and increasing the heat transfer rate when the fin length is increased to more than 1 m. Moreover, the distance between the ground heat exchanger and the fin is critical; if it exceeds 5 cm, it loses some effectiveness, although it is still useful for soil recovery. In general, the fin increases the soil contact area, and a fin of length one meter can increase heat transfer per unit of pipe length up to 20.7 %. Comparing horizontal and vertical ground heat exchangers in finned and non-finned modes revealed that both modes increase performance with the fin. Still, the horizontal pipe increases performance by about 3 % more than the vertical spiral with the same number of fins.

A floor slab of buildings can be used as a ground heat exchanger by equipping heat exchange pipes with a horizontal layout, namely energy slabs. The thermal performance of conventional energy slabs is relatively low due to the interference with the ambient air temperature. This fatal drawback can be overcome by installing energy slabs in an underground parking lot, where the influence of ambient air is not significant. This study experimentally investigated the applicability of two types of energy slabs (floor type and wall type), which were constructed on the basement slab in an underground parking lot. In particular, an aerogel-type thermal insulation layer was fabricated in each energy slab to isolate it from the ambient air along with enhancing the structural stability against automobiles. In the thermal performance tests, the constructed energy slabs showed a thermal performance 265% higher than the conventional energy slabs. Moreover, the aerogel-type thermal insulation layer effectively prevented surface condensation. However, the thermal stress of 2350 kPa was induced by the cooling operation in the energy slabs, which means the energy slab should possess sufficient tensile strength to secure the structural integrity of the parking lot basement. [ABSTRACT FROM AUTHOR]

Snow and ice forming on the entrance and exit driveways of underground car parks of buildings brings serious difficulties and risks in safe parking for vehicles in winter. Even though traditional methods such as chemical salt and snow plowing reduce slippery conditions on driveways, they also result in infrastructure- and environment-related damages. Hydronic heating is an alternative way to prevent snow and ice forming; thereby, the hydronic heating driveway (HHD) is a promising technique for energy-efficient and environment-friendly solutions. This study presents a time-dependent three-dimensional numerical heat transfer model for HHD applications with realistic boundary conditions and meteorological data in the MATLAB environment. After developing the numerical heat transfer model, the model is applied to a case study in Istanbul, Turkey and followed by an economic comparison with the commercial electrically-heated driveways (EHD) method that is applied in two different ways; applying the electric cables in (i) whole driveway and (ii) only tire tracks. Different escalation rates in natural gas and electricity, hot fluid inlet temperature, air temperature, and the number of parallel pipes are the main parameters in the case study. Results show that the decrease in pipe spacing drops the investment cost term but it needs a higher supplied fluid temperature for anti-icing, and therefore the operating cost term increases. Among other cases was the number of parallel pipes, with 50 being the most economically feasible solution for all air temperatures ranging from 0 °C to −10 °C. The economic comparison shows that the EHD with only tire tracks has the minimum total cost as it significantly decreased both the operating and investment cost terms. In case of an anti-icing requirement on the whole road surface, the HHD system was found to be preferable to the EHD whole driveway scenario at air temperatures of 0 °C and −5 °C, while it is more beneficial only for the high electricity escalation rates at the ambient temperature of −10 °C. [ABSTRACT FROM AUTHOR]

The ground-coupled heat pump is a shallow geothermal exploitation method taking soil as the thermal energy source. The ground heat exchanger is an important component of this system, which includes vertical or horizontal configurations. However, to the best of our knowledge, few studies exist involving the comparison of thermal performances and installation costs of two heat exchanger types considering the influence of ground climate, which makes the selection of heat exchanger configuration challenging for a specific field application. Hence, a 3-dimensional numerical model considering the variations of atmospheric conditions and soil water content is constructed in this paper. Based on this model, the thermal performances and economical efficiencies of vertical and horizontal ground heat exchangers are compared. The results indicate that the thermal performance difference between the two heat exchangers is greater in winter than in summer. The thermal performance is hardly influenced by the injection mass flow rate, while it is considerably affected by the length of heat exchanger. The thermal power rises linearly with the increase in heat exchanger length, and the increment of the vertical ground heat exchanger is higher. In addition, when the heat exchanger length is shorter than 40 m, the installation cost and thereby the total cost of the horizontal ground heat exchanger is considerably higher. With regard to both the thermal performance and economic efficiency, a vertical ground heat exchanger is only recommended when installing a single shallow ground heat exchanger. [ABSTRACT FROM AUTHOR]

The aim of the present study is to investigate the performance of water‐based brine solutions in the ground heat exchanger (GHX) for space heating applications under severely cold climate conditions. The conventional ethylene glycol (EG) and propylene glycol (PG)‐based water solutions have been considered for investigation. For the closed‐loop vertical U‐tube GHX, a mathematically built model is developed for ambient temperature below 0°C. The thermal performance analysis of GHX is carried out for the variation in fluid flow rate and brine solutions for different mixture percentages of water in EG and PG. The percentage of the mixture and fluid flow rate varied from 25% to 60% and 0.2 to 0.6 LPS, respectively. GHX performance parameters, namely convective coefficient, pressure drop, borehole resistance, and GHX effectiveness are determined for both EG and PG brines. Better performance of GHX is noticed with EG brines as compared to PG brines for similar operating conditions. The drop in convective coefficient from 22% to 44% in the case of PG brines as compared to EG brines with the increase in mixture percentage from 25% to 60%, for the same operating conditions. The pressure drops decreased from 15% to 74% for EG mixture as compared to PG mixture at considered flow rate and mixture percentage. The effectiveness and overall borehole resistance were higher for EG as compared to the PG solution. [ABSTRACT FROM AUTHOR]

Strata thermal conductivity (λ e) influences efficiency of medium-depth ground heat exchangers. However, a systematic approach to the acquisition of λ e is still lacking. Hence, stratigraphic heat conduction was analyzed using geophysical test in Shenyang, combined with composite modeling. Cenozoic strata (0–730m) exhibited an average λ e of 1.32 W·m−1·K−1 due to higher porosity and mud content; Archaean (730–2500m) strata displayed a higher λ e of 2.80 W·m−1·K−1, due to dense quartz sandstone with lower porosity and mud content. The CBHE in Shenyang can achieve excellent heat extraction relying on good thermal conduction. Spearman correlation revealed strong negative correlations between λ e and acoustic time difference, permeability, and porosity, while positive correlations were observed with depth, resistivity, wave speed, and rock skeleton. Higher rock skeleton thermal conductivity intensified the decrement effect of mud content on λ e , while higher mud content diminished the enhancement effect of rock skeleton thermal conductivity. As porosity increased, the decline in λ e slowed, particularly pronounced at higher saturation levels. λ e exhibited a gradual decrease with temperature, with a more notable change rate observed at lower porosity levels. Principles for enhancing thermal conduction were elucidated through a three-phase analysis. These findings provide foundation for the study and design of medium-depth boreholes. [Display omitted] • Conducted geological tests at a depth of 2500m in Shenyang, southern Songliao basin. • Created a combined thermal conductivity model considering temperature correction. • Analyzed the correlation and influence mechanism of geological factors. • Dense and hard rock formations (low porosity and mud content) favor thermal conduction. [ABSTRACT FROM AUTHOR]

• An innovative integrated BIPVT, ground heat exchanger, and liquid desiccant system. • Electricity and thermal load of a residential building located in hot and humid climate is supplied. • The building energy consumption is reduced by about 32%. • The levelized cost of electricity of the system varies between 2.25 $/kWh and 4.10 $/kWh. • The system environmental impacts are lower than the conventional system except ADPE and FW indexes. Today, using integrated renewable energy systems in residential buildings is a solution that, in addition to reducing energy consumption in this sector, also leads to proper placement and economic efficiency. In this study, an innovative integrated solar-geothermal system consisting of a building integrated photovoltaic-thermal system, the ground heat exchanger, and the liquid desiccant system with low regeneration temperature is investigated to provide electricity, domestic hot water, space heating and cooling annual needs of a residential building located in a dense urban fabric of hot and humid climate. The energy, economic, and environmental analyses of the integrated system are dynamically studied using TRNSYS-MATLAB co-simulator. By defining a system control method, the integrated system is able to provide about 2500 h of the total space cooling needs passively by only the ground heat exchanger, while the ground temperature has a very little change in the long-term. Also, using the integrated renewable energy system, the building energy consumption is reduced by about 32 %, and the system overall efficiency is obtained about 45 %. The economic analysis showed that the risk of initial investment return in less than 8 years and the risk of increasing the internal rate of return to more than 18 % for the integrated system are 49 % and 17 %, respectively. Also, based on the results of the stochastic model, the levelized cost of electricity of the system varies between 2.25 $/kWh and 4.10 $/kWh. It is found from the environmental analysis that all the environmental impacts of the proposed system are lower than the conventional system except ADPE and FW indexes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive review of GSHPs for cold climate applications is presented. • A systematic methodology to classify and evaluate various ground heat exchanger designs. • Critical analysis of GSHP performance improvement using solar thermal energy and thermal storage systems. • Review of control and optimization strategies for heat pumps in cold climates. Increasing concerns over anthropogenically-induced climate change are driving the search for alternative, renewable, clean technology to generate energy. Heat pumps are an efficient means of transitioning towards renewable energy sources for space heating, space cooling, and water heating in buildings. The common types of heat pumps are air source heat pumps, which use the ambient air as the energy source and sink, and ground source heat pumps (GSHPs), which use the more stable ground temperatures as the source and sink. In cold climates, the performance of both systems may be compromised, demanding careful design, optimization, and enhancement. GSHPs have the most excellent potential in cold climates where heating loads are significantly higher than cooling loads owing to their use of the more stable ground temperatures. Therefore, this paper provides a comprehensive review of GSHP systems for cold climates, beginning by first introducing the GSHP technology, including a summary of geothermal system classifications and a review of global GSHP systems and their applications. This is followed by an overview of closed-loop systems, including different configurations of ground heat exchangers, and a look at recent innovations in the design of GSHPs. Moreover, studies on the design and performance improvements of open-loop systems are discussed. As a means of improving system performance in cold climates, this paper presents a review of hybrid systems developed by several researchers. Additionally, insights on using GSHP systems for district heating and incorporating thermal storage systems to improve overall system performance are examined. Finally, the control and optimization strategies, as well as economic feasibility and environmental impacts, are reviewed. This study shows the potential to reduce thermal interference radius, thermal imbalance and the length of the heat exchanger when using GSHP systems with latent thermal storage systems and solar recharging. Nonetheless, a need remains for more robust and accurate dynamic prediction models for hybrid heating systems with GSHPs to assess long-term performance and cost-effectiveness. [ABSTRACT FROM AUTHOR]

[Display omitted] • Performance of medium-deep geothermal heat exchanger was studied. • Logging data and tested heat exchanger performance were presented. • Algorithm was validated with less than 10.65% relative error after stabilization. • Heat exchange rate varies from 169 kW to 517 kW under different operating parameters. • Lifecycle carbon emission changes from 18.5 kg·kW−1 to 9048.8 kg·kW−1. Geothermal energy is one of the most competitive renewable energies and the medium-deep geothermal energy has been broadly adopted for building heating. This paper reported a long-term performance study on the medium-deep ground heat exchangers (GHEs) based on a project in Xixian New Area, China. The logging data of a 2,500 m well and the tested inlet/outlet temperature were presented, before a numerical simulation algorithm was validated and adopted to predict the GHE long-term performance affected by operating parameters. It turns out that the algorithm can forecast the performance with a maximum relative error of less than 10.65 % at the stabilization stage. Under long-term operation, the average heat exchange rate becomes stable since the eighth year. The heat exchange rate varies from 169 kW to 517 kW through the life cycle when changing flow rate and daily operating time. The carbon emission needed for per unit heat extraction ranges from 18.5 kg·kW−1 to 9,048.8 kg·kW−1. Properly adjusting the operating parameters according to the building load will be beneficial to reducing carbon emissions and improving heat extraction efficiency. It is expected that the results will be conducive to the high-efficiency and low-carbon usage of geothermal energy. [ABSTRACT FROM AUTHOR]

A ground-source heat pump (GSHP) system is a renewable energy technology that effectively reduces greenhouse gas emissions and consequently mitigates the progression of global warming. The thermal efficiency of ground heat exchangers (GHEs) is a critical component in the GSHP system that must be accurately estimated for its long-term operationality. Therefore, in this study, the thermal performance of double-spiral GHEs incorporated within the thermal piles of a zero-energy building in Sapporo, Japan, was investigated using the actual measured data obtained from the site and a novel metric, namely, the coefficient of heat extraction/injection, for a more precise evaluation. Moreover, this study assessed the coefficient of performance (COP) of the GSHP units during various periods of cooling or heating. The temperature of the circulating fluid remained within an ideal operational range over an operational period of 2 years, and the COP calculations indicated a high operational efficiency. The results derived in this study substantially exceeded those of traditional U-tube GHEs, indicating the enhanced efficiency and superior performance of large-diameter thermal piles with augmented thermal capacity. Our findings suggest that GSHP systems with double-spiral-tube GHEs have superior efficiency than conventional GHEs.

The dynamic performance of a hybrid power plant configuration comprising of a ground heat exchanger and an organic Rankine cycle (ORC) for power generation at the load end is studied. The ground heat exchanger, reservoir, boiler and ORC heat exchanger are modelled using simplified energy equations-based reduced-order models. The developed numerical models are validated against the results obtained from published literature, and agreeable accordance is found in the simulated trends. The simulations are performed to illustrate the advantage of using insulation in the ground heat exchanger. The time required for the stabilisation of outlet temperature in a borehole heat exchanger (BHE) is estimated from the computational results. The simulation of dynamic characteristics demonstrates that the proposed geothermal-ORC hybrid system is capable of producing a steady power output of approximately 86.3 kWt. The exergy efficiency of U-shaped BHE without insulation is found to be the maximum.

As a promising alternative to conventional heat transfer fluids, microencapsulated phase change material slurry (MPCS) was applied in ground heat exchanger (GHE) in this paper. A sandbox system embedded with horizontal serpentine GHE was installed and MPCS using N-eicosane (C 20 H 42) as phase change material is prepared. To explore the merits of MPCS, a comparison study between performance of water and MPCS was conducted. In addition, the enhanced heat transfer mechanism of MPCS were studied by comparing performance of MPCS with different inlet temperature and particle concentration. The experimental results indicate that the heat transfer rate and pumping consumption of 25 wt% MPCS with inlet temperature of 30 °C are 10.5 and 2.8 times that of water, respectively. The heat load-to-pumping consumption ratio has an enhancement of 3.73 times in comparison to water. Obviously, considering the phase transition process, MPCS can efficiently improve thermal performance of GHE. However, in the non-phase transition temperature range, the performance of MPCS is even worse than that of water. The comprehensive performance factor of 15 wt% MPCS and 25 wt% MPCS with inlet temperature of 38 °C declined by 45.6% and 36.9% in comparison with pure water. [ABSTRACT FROM AUTHOR]

Geothermal energy is one type of renewable source of energy that can be used as shallow geothermal system for the use of cooling and heating of residential and commercial buildings. In this paper, an intense review is carried out on geothermal heating and cooling for air conditioning with a focus on Earth-Air Heat Exchanger (EAHE) and Ground Source Heat Pump (GSHP) systems. The study is carried out to understand the factors which have a significant effect on the performance of the EAHE and GSHP systems. This paper also focuses on the hybrid work of geothermal heating and cooling system with other forms of energy and provides benefits for designing efficient GSHP and EAHE systems. This study indicates that the important parameters for EAHE and GSHP systems are the thermal conductivity of soil, the water content present in the ground will significantly improve the performance of the systems, and further benefits are discussed in this study. [ABSTRACT FROM AUTHOR]

This paper presents proposals for using the direct-contact gravel, ground, air heat exchanger in single-family residential buildings with a passive house standard, according to the Passive House Institute (PHI). The methodology of their application consists of using heat and cold from the ground at an insignificant depth (about 1.5–4.0 m below the ground level for the central European climate) through an aggregate that is buried in the ground. This solution of simple installations is used for preheating and cooling fresh air drawn into the building through a mechanical ventilation system with heat recovery. In more complex applications it can be integrated with the source of heat and cold in passive buildings to create complete heating, cooling, and ventilation systems. In both cases, the air flowing through the exchanger is cooled and dried in summer, heated and humidified in winter, and filtered from pollen and bacteria all year. Direct contact of the deposit with the surrounding native soil facilitates rapid regeneration of the bed temperature. This article presents several proposals for integration with systems ensuring climatic comfort in a passive building, as exemplary applications. The paper presents preliminary estimates of energy (savings of up to 70% of electrical energy consumed), economic (SPBT = 3.65 years), and environmental (69.5% reduction in CO2 emissions) benefits related to implementing this solution in various configurations of technological systems for buildings in Poland. The calculations were carried out for the city of Poznań, taking into account the hourly intervals and using the author's code written in MS Excel. The analysis of the operation of the direct-contact gravel, ground, air heat exchanger (GGAHE) system is based on a theoretical heat and mass exchange model. The integrated solutions of technical systems presented in this article provide an interesting alternative to traditional heating, cooling, and ventilation systems. [ABSTRACT FROM AUTHOR]

The borehole thermal resistance (mK/W) is an essential design factor of a ground source heat pump system, which allows to predict changes in the circulating fluid temperature. However, there are no proven and/or practical solutions to the borehole thermal resistance of ground heat exchangers with large borehole diameters and multiple U-type pipes, such as a large-diameter cast-in-place energy pile. In this study, empirical formulas were provided to estimate the borehole thermal resistances of large-diameter cast-in-place energy piles equipped with multiple pairs of U-type heat exchange pipes. First, the borehole thermal resistances of parallel U-type energy piles were evaluated through a series of in-situ thermal performance tests. Then, a numerical model for parallel U-type energy piles was developed and verified using the field test results. With the developed numerical model, the effects of various influencing factors on the borehole thermal resistances of parallel U-type energy piles were identified. Finally, empirical formulas were developed and verified by comparing with the field tests and numerical simulations. Consequently, the empirical formulas could predict the borehole thermal resistance of parallel U-type energy piles with a difference of less than 0.23% compared to the numerical model and 6.4% compared to the field test results. [ABSTRACT FROM AUTHOR]

Heat pumps are the ideal solution for powering new passive and low-energy buildings, as geothermal resources provide buildings with heat and electricity almost continuously throughout the year. Among geothermal technologies, heat pump systems with vertical well heat exchangers have been recognized as one of the most energy-efficient solutions for space heating and cooling in residential and commercial buildings. A large number of scientific studies have been devoted to the study of heat transfer in and around the ground heat exchanger. The vast majority of them were performed by numerical simulation of heat transfer processes in the soil massif–heat pump system. To analyze the efficiency of a ground heat exchanger, it is fundamentally important to take into account the main factors that can affect heat transfer processes in the soil and the external environment of vertical ground heat exchangers. In this work, numerical simulation methods were used to describe a mathematical model of heat transfer processes in a porous soil massif and a U-shaped vertical heat exchanger. The purpose of these studies is to determine the influence of the filtration properties of the soil as a porous medium on the performance characteristics of soil heat exchangers. To study these problems, numerical modeling of hydrodynamic processes and heat transfer in a soil massif was performed under the condition that the pores were filled only with liquid. The influence of the filtration properties of the soil as a porous medium on the characteristics of the operation of a soil heat exchanger was studied. The dependence of the energy characteristics of the operation of a soil heat exchanger and a heat pump on a medium with which the pores are filled, as well as on the porosity of the soil and the size of its particles, was determined. [ABSTRACT FROM AUTHOR]

The applications of ground heat exchangers (GHEs) in arid and semi-arid zones require knowledge about the effects of moisture on heat transfer in the ground. To evaluate the influence of moisture, this study integrates a finite line-source model, a normalized thermal conductivity model, and a saturation degree model. A normalized temperature difference, defined as a temperature-difference ratio (TDR) of unsaturated to saturated soils, is proposed to characterize the reduction in heat transfer of GHEs in unsaturated soils. The modeling results show that the effective thermal conductivity of soils increases with saturation degree in a nonlinear way, thus leading to the nonlinear effect of moisture on heat conduction of GHEs: the influence of moisture on heat transfer is more significant in low-moisture soils (S l < 0.5) than that in high-moisture soils (S l > 0.5). This result implies that the design length of borehole GHEs is highly sensitive to the degree of saturation in low-moisture soils. • This study evaluates the influence of moisture on heat transfer of GHEs. • Heat transfer of GHEs is highly sensitive to saturation in low-moisture soils. • A closed-form equation for temperature-difference ratio (TDR) is proposed. • TDR characterizes the reduction in heat transfer of GHEs in unsaturated soils. [ABSTRACT FROM AUTHOR]

The authors present the development of a novel software and hardware package that dynamically predicts future ground heat exchanger temperatures to avoid thermal imbalance and future ground source heat pump system failure. In this study, an energy meter was installed on the ground heat exchanger of an office building and software was created on a remote server that collected the measured data. The future ground temperature was dynamically calculated, and the prototype was integrated with the building automation system to prevent future ground source heat pump system failure. The results showed that the building was cooling dominate and if the current mechanical system operation continued, the system would become inefficient in 16 years from high inlet temperatures to the heat pumps. A control sequence was developed for mitigating ground heat exchanger failure on the studied building. It was also determined by adjusting the set-point temperature of the make-up air unit from 12.8°C to 4.8°C, the amount of heating performed by the ground source heat pump system would increase to 49,230 kWh which maintained the calculated 20-year ground heat exchanger temperature below 32°C. The prototype developed in this paper is critical for maintaining an efficient ground source heat pump system and adequate ground heat exchanger temperatures. The outcome of this study provides the solution of ensuring a successful adoption of sustainable green technology on a large scale and eliminates ground source heat pump system failure due to thermal imbalance. [ABSTRACT FROM AUTHOR]

Renewable energy resources have become a promissory alternative to overcome the problems related to atmospheric pollution and limited sources of fossil fuel energy. The technologies in the field of renewable energy are used also to improve the ventilation and cooling in buildings by using the solar chimney and heat exchanger. This study addresses the design, construction and testing of a cooling system by using the above two techniques. The aim was to study the effects of weather conditions on the efficiency of this system which was installed in Baghdad for April and May 2020. The common weather in these months is hot in Baghdad. The test room of the design which has a size of 1 m3 was situated to face the geographical south. The test room is thermally insulated and connected to a solar chimney which generates a convection current to draw the air out of the room through a heat exchanger. The heat exchanger was submerged in a water tank of 2 m length, 1 m width and 1 m height. It was also covered with a layer of soil mixture with a thickness of 10 cm. The experiment simulates the natural conditions of a shallow water surface, connected to the room from the other side. The study results revealed that the air temperature inside the test room was lower than that of the ambient air outside. Pearson correlation coefficient showed that there was a strong direct relationship between solar radiation, temperature and wind speed from one side and the cooling efficiency from the other side. Also, there was a negative correlation between relative humidity and cooling efficiency.

The use of electrical energy for heating and cooling systems to control the temperature in greenhouses will lead to high production and product costs. To solve this problem, shallow geothermal energy as a local source of energy could be applied. In this study, a measurement model, the distribution profiles of temperature, and a preliminary assessment of the geothermal potential in the shallow zone at depths of 0.1 m to 3.6 m in Shouguang City, Shandong Province, eastern China were presented. The measurement results showed that the annual average temperature at depths of 0.1–3.6 m ranged from 13.1 °C to 17.6 °C. Preliminary assessment results of the geothermal potential showed that the daily average temperature difference between the air and at depths of 1.5–3.6 m was mainly from 10 °C to 25 °C during the winter months and between −15 °C and −5 °C during the summer months. Therefore, the heating systems could operate during January, February, November, and December. In May, June, and July, the cooling systems could be applied. Moreover, the measurement model gave good stability results, and it could be used in combination with the monitoring of the groundwater table, a survey of the thermal conductivity of the soil, climate change studies, which helps reduce unnecessary time and costs.

Accurately estimating the dimensionless ground thermal response factor (g-function) is critical for the design and operation of geothermal energy systems. This process, however, is fraught with uncertainties stemming from the difficulty in controlling on-site geometric parameters and estimating thermal properties through field experiments. The relative contributions of these parameters to response uncertainty change temporally as the response progresses. Thus, understanding this temporal sensitivity variation is crucial for effective response uncertainty management. To address this, we conducted transient global sensitivity analyses. Regardless of borefield setups, ground thermal properties were key factors in thermal response uncertainty. However, their influence decreased from the late-mid term as borehole radius and borehole distance became more significant in single-borehole and multi-borehole setups, respectively. This time-varying relative sensitivity suggests that prioritizing parameters to reduce response uncertainty depends on the temporal characteristics of the ground load. To demonstrate this, we systematically halved the uncertainty for each parameter and examined the resultant change in the fluid temperature uncertainty for a dynamic ground load scenario. Notably, prioritizing parameters with high early-response sensitivity significantly reduced fluid temperature uncertainty. These findings highlight the need for dynamic uncertainty management strategies in geothermal system design and operation. For dynamic load profiles utilizing the ground as a heat source or sink, prioritizing parameters with high sensitivity in the early- to mid-term is crucial. Conversely, for long-term storage applications, focusing on parameters with high sensitivity in the mid- to long-term response becomes essential. • Analyzed time-dependent parameter contributions to ground thermal response uncertainty • Clarified temporal changes in parameter contributions using transient global sensitivity analyses • Demonstrated relative parameter sensitivity to response uncertainty varies dynamically over time • Identified key influential parameters on response uncertainty depends on temporal load patterns • Dynamic uncertainty management is required considering temporal sensitivity and load patterns [ABSTRACT FROM AUTHOR]

• Quasi-steady-state model of deep borehole handles geothermal gradient. • Geothermal gradient may delay or prevent development of quasi-steady-state period. • Geothermal gradient affects TRT estimates of borehole and ground properties. • Choice of fluid inlet in coaxial borehole changes geothermal gradient effects. • As parameter | q ratio | decreases to 1 or less, models must include geothermal gradient. A thermal response test (TRT) on a borehole provides information needed in the design of ground heat exchangers for ground source heat pump systems. Conventional analysis of TRT data sets uses the late-time period to estimate the ground thermal conductivity and the effective borehole resistance. During this quasi-steady-state period, the transient average fluid temperature has a logarithmic linear trend, which is consistent with conventional heat transfer models that assume a uniform undisturbed ground temperature. As the depth of the borehole increases the undisturbed ground temperature increases with depth following the geothermal gradient. This paper focuses on how the geothermal gradient affects a TRT. As the geothermal gradient increases, the required time to reach the conventional logarithmic linear trend may increase beyond any practical testing duration in coaxial boreholes. Then, conventional analysis methods based on a quasi-steady-state period incorrectly estimate the ground thermal conductivity. The magnitude of this effect is controlled through a dimensionless parameter | q ratio |, which includes the geothermal gradient and other test parameters. In place of conventional models, a transient model that includes the geothermal gradient and fluid thermal storage can estimate the ground thermal conductivity and local borehole resistance within the typical TRT testing duration. [ABSTRACT FROM AUTHOR]