With the constant increase in energy demand, using renewable energy has become a priority. Geothermal energy is a widely available, constant source of renewable energy that has shown great potential ...as an alternative source of energy in achieving global energy sustainability and environment protection. When exploiting geothermal energy, whether is for heating or cooling buildings or generating electricity, a ground heat exchanger (GHE) is the most important component, whose performance can be easily improved by following the latest design aspects. This article focuses on the application of different types of GHEs with attention directed to deep vertical borehole heat exchangers and direct expansion systems, which were not dealt with in detail in recent reviews. The article gives a review of the most recent advances in design aspects of GHE, namely pipe arrangement, materials, and working fluids. The influence of the main design parameters on the performance of horizontal, vertical, and shallow GHEs is discussed together with commonly used performance indicators for the evaluation of GHE. A survey of the available literature shows that thermal performance is mostly a point of interest, while hydraulic and/or economic performance is often not addressed, potentially resulting in non-optimal GHE design.
•A new hybrid gravity heat pipe system is proposed, which uses PPR material for the insulation section and copper material for the evaporation and condensation sections.•During the experimental ...period, both heat pipe systems showed good thermodynamic properties and the soil temperature in the experimental area increased significantly.•Copper and PPR pipe joints make the HGHP thermal resistance greater than CGHP, and the heat transfer capacity of HGHP decreased by 22.68% compared to CGHP.•The cost analysis found that the HGHP cost was 48.39% lower than the CGHP due to the use of low-cost PPR materials.
ravity heat pipe is a highly efficient heat transfer device that shows great potential for efficient development of shallow geothermal energy.The adiabatic section of the gravity heat pipe does not exchange heat with the external environment during operation, and the use of low-cost PPR materials with low thermal conductivity to replace the expensive metal materials in the adiabatic section can significantly reduce the cost of gravity heat pipe materials.In this study, a new hybrid gravity heat pipe (HGHP) composed of metallic copper and PPR materials is designed, in which the evaporation section and condensation section, which exchange heat with the external environment, are made of metallic copper, and the adiabatic section, which does not exchange heat with the external environment, is made of PPR material, and the analysis of HGHPs and heat transfer characteristics of the similar principle has not yet been reported in the public literature.It was found that the average soil temperature around the condensation section of CGHP and HGHP during the experimental period increased by 4.94℃ and 3.08℃, respectively, compared to the soil temperature of the control group without heat pipe, which was a significant warming effect;Both sets of heat pipes exhibit good isothermal performance,and the CGHP isothermal performance is better than the HGHP;The thermal power of CGHP and HGHP is 55.11 and 42.61 W respectively, which is 22.68% lower than that of CGHP due to the increased thermal resistance of the connecting joints of HGHP.The cost analysis found that the cost of HGHP is 48.39% lower than that of CGHP, and the material cost decreases significantly. This study provides a feasible solution to reduce the cost of shallow geothermal energy development.
Constructed wetland is an efficient and convenient wastewater treatment technology that has been widely used in China and elsewhere. However, seasonal frozen soil is easily formed in the cold regions ...of northern China. The local wetlands are in the frozen soil layer, causing the pollutants from wastewater not to be removed well. Therefore, a new constructed wetland structure that uses shallow geothermal energy to keep the wetland not frozen in the winter is proposed in this paper. The results of the experiment show that the average removal rates of total nitrogen, ammonium ion, and total phosphorus in the multistage constructed wetland system are 54.8%, 44.5%, and 77.7%, respectively. This performance is substantially better than that of conventional wetlands in winter. The proposed wetland structure can be applied to conventional wetlands and avoid the conventional wetlands being idle during cold seasons, which is conducive to the popularization of constructed wetlands (CWs) in cold regions.
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•A new subsurface flow constructed wetland using shallow geothermal energy is proposed.•The proposed wetland system can keep not frozen in winter.•The new wetland structure showed good performance especially on removal of TN and NH4+-N by using shallow geothermal energy in winter.•The performance of the proposed wetland is substantially better than that of conventional wetlands in winter.•Using shallow geothermal energy for wetland insulation is more suitable for applying in cold regions of northern China than those of existing methods.
Energy geo-structures utilise underground structures primarily designed for structural and geo-mechanical stability to also provide renewable geothermal energy for heating and cooling purposes. ...Piping is incorporated in the structures to exchange heat with the ground via a carrier (water) and connected to a ground-coupled heat pump on the building side. This work focuses on energy diaphragm walls, expanding on the limited available knowledge and undertaking a comprehensive parametric analysis using experimentally validated numerical modelling. Focus is put on the wall pipe configuration and spacing, which are parameters the geothermal design can directly control, however, the effects of ground thermal conductivity and wall depth are also considered. The wall depth is shown as a critical factor to the thermal performance and low thermal conductivity material sites might require deep energy walls for a cost-effective design. Larger pipe spacing (≥500 mm) appears preferable, despite less piping being placed, since small spacing leads to increased costs but insignificant thermal performance gains. Comparing the horizontal and vertical pipe configurations, relatively small temperature differences of less than 1 °C are found. Moreover, the former can be less expensive for multiple-section deeper walls, while the latter for shorter walls or when construction delays are non-critical.
•The retaining wall depth is critical to the thermal performance of energy walls.•Larger pipe spacings result in more cost-effective energy diaphragm wall designs.•The site material thermal conductivities do not affect the choice of pipe spacing.•Vertical and horizontal pipe configurations result in similar thermal performance.•Vertical configurations may result in construction delays based on splicing numbers.
The residential building sector is recently experiencing a large reduction of energy demand for conditioning, nevertheless, the use of energy in agro-industrial productions is constantly growing and ...the research of alternative and more sustainable sources has become necessary. In the greenhouses production, the energy problem is relevant since high demand is required, even for long periods with considerable peak requests and the use of renewable energy sources in such productions can allow a significant reduction of fossil fuel consumptions, greenhouse gas emissions and running costs.
In this context, this paper analyses the performance of a low-enthalpy geothermal system, consisting of basket geothermal heat exchangers with a ground source heat pump, specifically studied to provide the base load for winter heating demand of a greenhouse. Due to the large thermal demand requested by the greenhouse, the existent pressurized gas boiler and two existent air source heat pumps, now also converted to work in heating mode, cover the remnant demand. Based on the thermo-hygrometric data, collected during an experimental campaign carried out on a case study farm, the study evaluates the performance of the geothermal system prescribing the optimal thermo-hygrometric conditions requested for the production of three different protected crops. The shallow geothermal field operates mainly during the night-time, allowing the thermal recover of the ground during the daytime. The results provide an assessment of the performances of the hybrid system in terms of primary energy needs, running costs and CO2 with respect to the existent system.
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•BGHE used in hybrid configuration can improve greenhouse cultivation sustainability.•The performance of the shallow geothermal field is evaluated and discussed.•The numerical results are obtained from experimental data.•Hybrid system allows primary energy savings from 20% to 40%.•GHG emissions and running costs can be reduced from 10% to 30%.
The combined use of solar energy and ground-source heat pump system may provide a reasonable solution to the energy crisis and low utilization efficiency of single energy. Herein, a numerical model ...of a solar assisted hybrid ground-source heat pump (SAHGSHP) system composed of multiple types and lengths of borehole heat exchanger (BHE) array was developed. The effectiveness of this model was validated by experimental data of a SAHGSHP system located in Tongzhou, Beijing. The verified model was used to study the performance sustainability of SAHGSHP system under different seasonal operation modes and its influence on the temperature of rock and soil. It was shown that for different types of BHEs in heat extraction periods of SAHGSHP systems, the outlet temperature decline rate decreases by an average of 2.30%, the temperature decline rate of rock and soil at the reference point under single-season operation decreases by an average of 0.78%, and the temperature increase rate of rock and soil at the reference point under double-season operation increases by an average of 0.53% compared with that of hybrid ground-source heat pump (HGSHP). The results of this study could provide a further understanding for analyzing the seasonal operation mode of SAHGSHP.
Ground Source Heat Pumps (GSHPs) have been installed all around the world to harvest shallow geothermal energy for heating and cooling building envelopes. However, the high initial cost of these ...systems (e.g., drilling and installation costs) limits the popularity and total usage of GSHPs around the world. To reduce the initial cost of these systems, geothermal heat exchangers are combined with structural components of the building, such as deep foundations, or energy walls. Energy piles or thermo-active foundations that serve dual purposes have been widely utilized in the last two decades in many developed countries. However, in most of the developing countries like Iran, there are several critical impediments to install these systems to harvest shallow geothermal energy. This study aims to propose practical suggestions to increase the rate of energy piles installation as an alternative environmentally friendly energy system to heat and cool residential and commercial buildings in Iran by I) summarizing the lessons learned from energy piles projects in different countries, II) providing crucial information regarding design, construction, and implementation of energy piles to prepare a design code based on Iran's economic and environmental condition, III) reporting disadvantages of energy piles to determine challenges for engineers to find a solution for minimizing these issues, and IV) proposing key impediments in the way of implementation of energy piles in Iran and providing some practical suggestions to tackle these impediments.
•Lessons learned from energy pile projects in developed countries are summarized.•Various models developed for geothermal piles are discussed thoroughly.•Geothermal energy potentials in Iran are discussed.•The current status of energy piles in Iran is presented.•Challenges and practical suggestions for energy pile implementation in Iran are expressed.
Shallow ground-source heat pumps (GSHPs) are a promising technology for contributing to the decarbonisation of the energy sector. In heating-dominated climates, the combined use of GSHPs for both ...heating and cooling increases their technical potential, defined as the maximum energy that can be exchanged with the ground, as the re-injection of excess heat from space cooling leads to a seasonal regeneration of the ground. This paper proposes a new approach to quantify the technical potential of GSHPs, accounting for effects of seasonal regeneration, and to estimate the useful energy to supply building energy demands at regional scale. The useful energy is obtained for direct heat exchange and for district heating and cooling (DHC) under several scenarios for climate change and market penetration levels of cooling systems. The case study in western Switzerland suggests that seasonal regeneration allows for annual maximum heat extraction densities above 300 kWh/m2 at heat injection densities above 330 kWh/m2. Results also show that GSHPs may cover up to 63% of cooling and 55% of heating demand for individual GSHPs in 2050 in Switzerland, which increases to 87% and 85% if DHC is used. The regional-scale results may serve to inform decision making on strategic areas for installing GSHPs.
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•Technical potential of shallow ground-source heat pumps (GSHPs) at regional scale.•Seasonal regeneration of GSHPs by re-injection of space cooling needs to the ground.•Useful potential for supplying building energy demand under three climate scenarios.•Impact of district heating and cooling (DHC) on the useful potential of GSHPs.•Case study in western Switzerland: Up to 87% of energy potentially supplied for DHC.
Shallow temperatures down to a depth of 100 m were measured over one year in 19 closed boreholes located in Nanjing, China, to reveal the conditions and factors influencing the subsurface thermal ...regime. A monitoring concept with distributed temperature sensing, fiber Bragg grating-based sensor, and a type of Resistance Temperature Detectors, is implemented, providing spatial distribution characteristics of subsurface temperatures. The results show that temperatures near the surface are most dynamic, influenced by the air temperature. The temperature remains stable at the depth of 10–20 m. The mean transition temperature is 18.1 °C. Borehole measurements are interpolated by using satellite images and surface temperature records to obtain large-scale surface temperature distributions and temporal variations of subsurface temperature. Geological and hydrological conditions are primary factors by affecting subsurface upward heat flux and heat loss. Urban land cover change and enhanced heat release from urbanization contribute to a subsurface urban heat island with intensities of 1.0–4.4 °C. The altered subsurface thermal regime is of primary concern for the management of shallow geothermal energy use. The monitoring concept in this study can provide spatially-temporally continuous profiles of subsurface temperature and become a reference for city-wide geothermal monitoring in other urban areas.
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