Search Results (49)

Geothermal heat pump systems (GHPSs) offer a sustainable and energy-efficient solution for heating and cooling buildings. Ground heat exchanger (GHE) design and configuration significantly impact on the overall performance and installation expenses of geothermal heat pump systems. This paper presents a comprehensive analysis of GHPSs, focusing on their advantages, disadvantages, key components, types, and particularly the various closed-loop GHE configurations. Detailed comparisons highlight how different designs affect thermal performance and installation costs. The findings reveal that helical GHEs offer superior thermal efficiency with reduced drilling requirements and cost savings, while coaxial GHEs, especially those using steel tubes, enhance heat transfer and enable shorter boreholes. Cost-effective options like W-type GHEs provide performance comparable to more complex systems. Additionally, triple U-tube and spiral configurations balance high efficiency with economic feasibility. The single and double U-tube remain the most common borehole geometry, though coaxial designs present distinct advantages in targeted scenarios. These insights support the optimization of vertical GHEs, advancing system performance, cost-effectiveness, and long-term sustainability in GHPS applications. Full article

This study presents a preliminary analysis of an innovative system that combines indoor air conditioning with water recovery and storage. The device integrates Peltier cells with a horizontal Earth-to-Air Heat Exchanger (EAHX), exploiting the ground stable temperature to enhance cooling and promote condensation. Warm, humid air is pre-cooled via the geothermal pipe, then split by a fan into two streams: one passes over the cold side of the Peltier cells for cooling and dehumidification, while the other flows over the hot side and heats up. The two airstreams are then mixed in a water storage tank, which also serves as a thermal mixing chamber to regulate the final air temperature. The analysis investigates the influence of soil thermal conditions on condensation within the horizontal pipe and the resulting cooling effect in indoor spaces. A hybrid simulation approach was adopted, coupling a 3D model implemented in COMSOL Multiphysics^® with a 1D analytical model. Boundary conditions and meteorological data were based on the Typical Meteorological Year (TMY) for Palermo. Two scenarios were considered. In Case A, during the hours when air conditioning is not operating (between 11 p.m. and 9 a.m.), air is circulated in the exchanger to pre-cool the ground and the air leaving the exchanger is rejected into the environment. In Case B, the no air is not circulated in the heat exchanger during non-conditioning periods. Results from the June–August period show that the EAHXs reduced the average outdoor air temperature from 27.81 °C to 25.45 °C, with relative humidity rising from 58.2% to 66.66%, while maintaining nearly constant specific humidity. The system exchanged average powers of 102 W (Case A) and 96 W (Case B), corresponding to energy removals of 225 kWh and 212 kWh, respectively. Case A, which included nighttime soil pre-cooling, showed a 6% increase in efficiency. Condensation water production values range from around 0.005 g/s with one Peltier cell to almost 0.5 g/s with seven Peltier cells. As the number of Peltier cells increases, the cooling effect becomes more pronounced, reducing the output temperature considerably. This solution is scalable and well-suited for implementation in developing countries, where it can be efficiently powered by stand-alone photovoltaic systems. Full article

The paper analyses multi-variant energy simulations carried out in IDA ICE 4.8 software for a newly designed single-family building within the framework of the 4E Idea. This idea assumes the use of energy-saving, ecological, ergonomic, and economic solutions in construction and building operation. Energy simulations were conducted to evaluate the annual energy-saving potential of the developed architectural house concept, which incorporates ergonomic analyses and cost-effective construction solutions. Analyses were conducted to optimise the non-renewable primary energy index by selecting mechanical ventilation system (CAV or VAV) with heat recovery; the configuration of photovoltaic module installation in terms of their location and orientation; the exposure and type of solar thermal collectors (flat and vacuum); and the use of two types of heat pumps (air- and ground-source). The most favourable energy performance of the building was achieved with an HVAC system equipped with a VAV mechanical ventilation system with heat recovery, an on-grid photovoltaic installation, vacuum solar thermal collectors, and a ground-source heat pump with a horizontal heat exchanger. This configuration resulted in a primary energy index value of 2 kWh/m²/year. The results of the analyses carried out for the 4E building concept may serve as a reference point for future energy-efficient building designs aspiring to meet higher standards of sustainable development. Full article

Geothermal energy, as a clean, low-carbon, widely distributed, renewable and environmentally friendly energy source, plays an important role in the transition from traditional energy sources dominated by coal and oil to clean energy. Ground source heat pump technology is a key technological tool for developing geothermal energy for widespread use. Coaxial-cased heat exchangers are the core component of the ground source heat pump system, and their heat transfer performance directly affects the heat transfer efficiency and service life of the ground source heat pump system. According to the actual working conditions of coaxial-cased heat exchangers in fractured aquifers, the coupled pressure–temperature model of the heat transfer outside the borehole was created by considering the influence of the Joule–Thompson effect. For heat transfer inside the wellbore, a multi-layer long concentric cylinder wall model was developed to obtain the fluid temperature distribution within the wellbore. Results show that the heat transfer efficiency increases with the increase of thermal conductivity, water production and effective permeability of fractures. The positive and negative values of the Joule–Thompson coefficient reflect the trend of fluid temperature changing with pressure. The larger the absolute value is, the greater the temperature change is. The increase in the initial temperature of the injected water will lead to a decrease in the theoretical heat transfer. With the increase of the water injection rate and horizontal wellbore length, the heat recovery power will also increase significantly, but the optimal value needs to be considered comprehensively. The findings of the study can not only lay a theoretical foundation for the performance evaluation and optimal design of coaxial-cased heat exchangers but also have great significance in promoting the efficient development of geothermal energy. Full article

Backfill material used as a heat-transfer medium in boreholes of ground heat exchangers (GHEs) has a great influence on heat-transfer efficiency. Abandoned waste material causing environmental pollution has become a key issue around the world. To make full use of solid waste, backfill material made of waste fly ash in combination with graphite of high thermal conductivity was proposed. First, the thermal properties of cement/fly ash blended with different mass ratio of graphite were tested through laboratory tests. Then, a numerical model was established, in which the accuracy was validated based on a field test. Finally, an investigation of the long-term performance (over a period of 90 days) for four boreholes backfilled with natural sand, cement/fly ash, and cement/fly ash combined with different proportions of graphite was conducted through this numerical model, and the heat-transfer rates under constant inlet temperature in four boreholes decreased from 13.31, 44.97, 45.95, and 46.73 W/m to 14.18, 14.96, 15.66, and 16.19 W/m after the 90-day operation. Considering the influence of groundwater seepage, the horizontal groundwater flow had a positive impact, improving the long-term heat-transfer performance. The heat-transfer rates of four testing boreholes decreased from 44.46, 46.38, 47.22, and 47.68 W/m to 21.18, 21.93, 22.62, and 23.13 W/m. However, long-term groundwater seepage in a vertical direction caused a sharp decrease in the heat-transfer rate, and the values after 90 days were 10.44, 10.62, 10.78, and 10.81 W/m, which were the lowest of all the working conditions. The feasibility of using fly ash blended with graphite as backfill material was further validated through a comprehensive perspective, including indoor laboratory, field testing, and numerical simulation, which has rarely been conducted in previous research. Full article

Heat pumps are currently one of the most frequently applied heat sources in residential buildings. Ground source heat pumps are more reliable than air source heat pumps in terms of energy efficiency, especially in colder climates. However, they are more expensive and involve increased material inputs; therefore, multi-criteria analyses taking into account environmental and economic aspects seem necessary for the green design of these systems. The aim of this work was to analyze the environmental and economic impacts of the ground source heat pump providing heating for a family house located in eastern Poland, cooperating with three types of ground heat exchangers (each in two sizing options): helix, vertical and horizontal. The multi-criteria analysis was based on the life cycle assessment methodology using IMPACT 2002+ and life cycle costs methods. The lowest environmental impact was reported for the variants with vertical ground heat exchangers, mainly due to their high efficiency in the operation stage. On the other hand, the lowest economic impact was observed for the horizontal heat exchangers, which are not demanding in terms of material and construction costs. Final recommendations based on multi-criteria analysis propose the vertical probes as a sustainable solution, with a weighted sum indicator in the range 0.085–0.297 on 0–1 scale. Full article

The application of ground heat exchanger technology in backfill mines can actualize subterranean heat storage, which is one of the most effective solutions for addressing solar energy faults such as intermittence and fluctuation. This paper provides a 3D unsteady heat transfer numerical model for full-size horizontal backfill heat exchangers (BFHEs) with five configurations in a mining layer of a metal mine by using a COMSOL environment. In order to ensure the fairness of the comparative analysis, the pipes of BFHEs studied have the same heat exchange surface area. By comparing and evaluating the heat storage/release characteristics of BFHEs in continuous operation for three years, it was discovered that the helical pipe with serpentine layout may effectively enhance the performance of BFHEs. Compared with the traditional SS BFHEs, the heat storage capacity of the S-FH type is significantly increased by 21.7%, followed by the SA-FH type, which is increased by 11.1%, while the performances of U-DH and SH type are considerably lowered. Also, the impact of the critical structural factors (pitch length and pitch diameter) was further studied using the normalized parameters C₁ and C₂ based on the inner diameter of the pipe. It is discovered that BFHEs should be distributed in a pipe with a lower C₁, and increasing C₂ encourages BFHEs to increase the storaged/released heat of BFHEs. By comparatively analysing the effect of thermal conductivity, it is found that the positive effects of thermal conductivity on the performance of SH, U-DH, SA-FH, and S-FH type BFHEs are found to decrease successively. This work proposes a strategy for improving the heat storage and release potential of BFHEs in terms of optimal pipe arrangement. Full article

Among the various approaches to agriculture, urban greenhouse farming has gained attention for its ability to address food security and disruptions to global food supply chains. However, the increasing impact of climate change and global warming necessitates sustainable methods for heating and cooling these greenhouses. In this study, we focused on the potential of slinky-coil horizontal ground heat exchangers (HGHEs) to meet the energy demands of urban greenhouses, assuming they are installed beneath the greenhouse to optimize space utilization. Climate data, an energy consumption profile for a greenhouse being designed in La Pocatière (Québec, Canada) and in-situ ground thermal properties assessments were used to build numerical models using FEFLOW and to evaluate the performance of the HGHEs simulated. Four scenarios were simulated and compared to a base case, considering the greenhouse’s maintenance of a constant temperature above an HGHE limited to the greenhouse’s dimensions. Our findings reveal that a minimum of 7.1% and 26.5% of the total heating and cooling loads of a small greenhouse (133 m² area) can be covered by HGHEs installed at a 1.5 m depth when there is no greenhouse above. When installed under a greenhouse with a constant inside temperature of 21 °C, the coverage for heating loads increases to 22.8%, while cooling loads decrease to 24.2%. Sensitivity analysis demonstrates that the constant temperature in the greenhouse reduces the system’s reliance on surface temperature fluctuations for both heating and cooling, albeit with reduced efficiency for cooling. Full article

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. Full article

Earth–air heat exchanger (EAHE) systems are used to pre-heat or pre-cool air before entering into a building using shallow geothermal energy. Assessment of EAHE systems is important to quantify the profitability of these systems. For this purpose, an EAHE system built at ICUBE at the University of Strasbourg in the northeast of France was studied using energy and exergy analyses for a typical heating period (between 25 February and 3 March). Energy analysis was used to determine the heat gained by the air in the system during the studied period and to determine the Coefficient Of Performance (COP) of the system. Additionally, exergy analysis, which considered temperature, pressure, humidity, and the variation in the control volume boundary temperature, was realized to determine inefficiencies in the system by determining the exergy destroyed in each component of the system and evaluating its exergetic efficiency. Results showed that the heat energy gained using the system was around 63 kWh and that the exergetic efficiency of the system was about 57% on average. The comparison of exergetic efficiency between the EAHE components showed that the fan has the lowest performance and should be improved to achieve better overall performance. Full article

To explore the influence of complex terrain on wind characteristics of the surface layer and to better develop and utilize wind energy resources of high-altitude regions in central and western China, two typical topographies: the Qiaodi Village in Sichuan (in western China, site 1) and the Nanhua Mountain in Shanxi (in central China, site 2), were selected for this study. The diurnal and monthly variations of the atmospheric stability were contrasted at the two sites, according to the Obukhov length calculated by the eddy covariance data. The energy exchange process between complex underlying surfaces and the atmospheric boundary layer can be reflected to a certain extent by investigating the diurnal variation differences of the turbulent fluxes at the two sites. The results show that: (1) the dominant boundary layer at site 1 during nighttime is the neutral boundary layer, while at site 2 it is the stable; (2) the horizontal wind speed at 10 m above the ground is the highest (lowest) in the neutral (unstable) boundary layer at site 1, while it is the highest (lowest) in the neutral and weak-unstable (stable) boundary layer at site 2, and (3) the momentum flux, sensible heat flux, and latent heat flux all show unimodal diurnal characteristics. There is a 1 h lag in the flux peak at site 1 compared to site 2. Full article

Human interference with the Earth’s climate cannot be ignored any longer. Renewable energy sources need utmost attention in all energy sectors. For buildings, geothermal energy for heating, cooling, and domestic hot water is a sustainable solution. Horizontal ground heat exchangers (HGHE) demonstrate promising results with low installation costs. Research is focused on increasing their thermal performances by structural improvements and ground thermal proprieties improvements, with little research on using auxiliary heat to increase their performances. A numerical model for an HGHE was established to investigate the effects of auxiliary heat sources on the performances of the HGHE. The results demonstrate that heat transfer into the HGHE increases the overall ground temperature at the end of the heating season by 138.50% compared with no heat transfer from auxiliary heat sources. The ground freezing period decreased by approximately 24.74% by having a heated basement, approximately 40.20% by transferring heat with solar thermal panels, and approximately 62.88% by using both auxiliary heat sources. The difference between the undisturbed ground temperature and the ground temperature with no auxiliary heat sources at the end of the season was 3.45 °C. The difference between the undisturbed ground temperature and the ground temperature with all auxiliary heat sources resulted in 0.92 °C. Full article

The publication presents the results of research on soil temperature distribution at a depth of 0.25–3 m in three measurement locations. Two boreholes were located in Białystok in the temperate climatic zone and one measuring well was installed in Belmez in the subtropical climatic zone. Measurements were made in homogeneous soil layers in sand (Białystok) and in clay (Białystok and Belmez). Based on the results of the measurements, a simplified model of temperature distributions as a function of depth and the number of days in a year was developed. The presented model can be used as a boundary condition to determine heat losses of district heating pipes located in the ground and to estimate the thermal efficiency of horizontal heat exchangers in very low-temperature geothermal energy applications. Full article

This study evaluates low-temperature district heating (LTDH) networks with different geothermal heat sources under thermo-economic criteria. In particular, the heat and cold supply of modern neighbourhoods are taken into account in a dynamic simulation model built on the modelling language Modelica. Both horizontal and vertical ground heat exchangers (GHE) were investigated in respect to the load profiles of the consumers, depending on dimension as well as location. The selected base case represents a LTDH network near Stuttgart (Germany). The corresponding results of an annual simulation show that a horizontal GHE is suitable for pure heat supply and can reduce costs by up to 12% compared to a vertical system. This economic advantage remains when the cooling demand is considered. Subsequently, a variation of the system location was carried out. It is shown that horizontal GHEs operate more economically in northern regions, whereas vertical ones are more advantageous in regions with increased cooling demand. For both cases, possible savings of between 3.0% and 4.2% resulted from the simulations. The heating-to-cooling demand ratio was used as a first decision criteria to weigh-up between the two systems. Vertical GHEs were more economical than horizontal systems as soon as the ratio dropped below 1.5. Full article

Utilizing a deep Borehole Heat Exchanger (BHE) has been recognized as a clean, renewable, low-carbon-emission, and sustainable way for heating of residential buildings and greenhouses. In this study, the long-term performance of horizontal deep BHE in intermittent mode is scrutinized. In this regard, to predict the transient heat transfer process in the deep BHEs, a mathematical model is developed and then verified by using the experimental results. The effect various key parameters including flow rate of circulating fluid, undisturbed ground temperature, inlet fluid temperature, and ground thermal conductivity on the thermal performance of deep BHE in continuous and intermittent mode is studied. According to the results, increasing the flow rate of circulating fluid, undisturbed ground temperature, and ground thermal conductivity is favorable for heat extraction rate. Moreover, the effect of three specific parameters for intermittent operation including periodic time interval, flow rate ratio, and recovery period ratio on the long-term performance of horizontal deep BHE are scrutinized. Based on the results, by decreasing the periodic time interval and increasing the flow rate ratio, the mean heat extraction rate in the period of 30 years is increased and the mean borehole’s wall temperature is decreased. Furthermore, by increasing the recovery period ratio, the heat extraction rate increases significantly while the total extracted energy decreases. Full article