Underground Temperature Distribution Research Articles

Research on Sustainable Shallow Geothermal Potential in Jinan Start-Up Area, China

Shallow geothermal energy (SGE), as an important renewable energy, playing an important role in reducing carbon emissions. In order to efficiently and sustainably utilize SGE, field investigation and storage estimation are needed. In this study, the hydrogeological data obtained from the field exploration of Jinan Start-up Area were collected and compiled. By analyzing the geotechnical property data and thermal response test results, the information of geotechnical and thermal properties and underground temperature distribution characteristics were collected. Subsequently, the analytic hierarchy process (AHP) combined with the comprehensive index method (CIM) were used to classify the shallow geothermal potential of Jinan Start-up Area. The entire area was divided into a high-potential area, medium-potential area and general area, of which 92.2% was high-potential area. The preliminary results, combined with the parameters obtained from the testing, indicate that the SGE storage at a borehole depth of 120 m is estimated to be approximately 2.68 × 1012 kJ·K−1, while the heat exchanger power of the buried pipe at the same depth is calculated to be around 1.73 × 105 kW. Finally, suggestions are given for sustainable development and utilization of SGE in this area.

Mathematical modeling and periodical heat extraction analysis of deep coaxial borehole heat exchanger for space heating

The geothermal energy is considered as one of the most promising renewable techniques for district heating. The deep coaxial borehole heat exchanger (BHE) is an economic and efficient measure for extracting the geothermal energy from underground, which attracts numerous attentions recently. However, the researches on the influences of the operation modes on the periodical heat extraction performances of the deep coaxial BHE are rare. In this paper, an unsteady numerical model of the dynamic operation of the coaxial borehole heat exchanger is established, based on the principles of energy conservation and mass conservation. The proposed model is verified using the operating data from the literature. Space heating of a school building (located at Tianjin, China) is taken as a scenario, and different operation modes during the heating period are simulated and analyzed. Comparisons were carried out on four operating modes: the continuous operation mode, “16+8 mode” (run for 16 h and stop for 8 h), “12+12 mode” and “8+16 mode”. The recovery of underground temperature distribution during the winter holiday was studied. Results show that, except for the continuous operation mode, the differences between the other three modes on the total extracted heat throughout the whole year and during the 24 h within the 90th day are unobvious. Under the “12+12 mode”, when the BHE reaches the stable level, the heat extraction power can be maintained at 301.6–528.1 kW in the first year, and the decline rate lower than 15% during the 20-year operation period. In addition, at 1 m from the center of the tube and at depths of 500 m, 1000 m, 1500 m, and 2000 m, the recovery rates of the underground temperature distribution relative to the initial temperature during the winter vacation are 7.35%, 13.78%, 16.57%, and 17.74%, respectively.

Geothermal structure revealed by curie isothermal surface under Guangdong Province, China

Guangdong Province in Southeast China is noted for its numerous geothermal resources due to tectonic episodes, mainly occurred during the Cretaceous. The surface heat flow and geothermal gradient are the most direct ways to understand the temperature of the Earth. However, geothermal resources are poorly utilized in Guangdong Province due to limited numbers of boreholes and surficial hydrothermal fluids. To improve the understanding of underground temperature distribution in Guangdong Province, we have applied power-density spectral analysis to aeromagnetic anomaly data to calculate the depth of the Curie isothermal surface. Upward continuation is applied and tested to the magnetic data. The calculated Curie isotherm is between 18.5 km and 25 km below surface. The fluctuation in the depth range reflects lateral thermal perturbations in the Guangdong crust. In particular, the eastern, northern, western and coastline areas of the province have a relatively shallow Curie isotherm. By comparing the surface heat flow, geothermal gradient, distribution of Mesozoic granite-volcanic rocks, and natural hot springs, we conclude that during Mesozoic, magmatism exerted great influence on the deep thermal state of Guangdong Province. A shallow Curie isotherm surface, as well as numerous natural hot springs and high heat flow, show clear signatures of shallow heat sources.

Performance simulation of underground seasonal solar energy storage in hot summer and cold winter zone in china

To analyze the performance of underground seasonal solar energy storage in hot summer and cold winter zones in China, a three-dimensional model for heat storage was developed. This model has been validated by the data from Tianjin’s experimental system and the relative error stayed below 5% during the process. A simulation was conducted to analyze thermal energy storage from March to October. Underground temperature distribution and the change in heat flux at each boundary were obtained. Three control strategies, that is, Normal, Double, and Interval were studied and compared. The effect of different heat storage start times/months for long-term heat storage was compared and discussed. The results show that the surface heat flux is significantly affected by the ambient temperature, while the bottom and sides of the heat storage area are primarily affected by the temperature of that area. The rise in the internal energy in March by Double-strategy and Interval-strategy are, respectively, 1.52 times and 1.12 times of that by Normal-strategy. For four months of heating storage, the average monthly heat storage efficiency is 80.70%, 81.34%, and 80.83% in Normal, Double, and Interval strategies, respectively. For long-term heat storage, an earlier start time/month lowers the efficiency of the system.

Underground temperature distribution and spatial suitability assessmentfor geothermal heat pumps in the alluvial fan of the Nagara River, central Japan

Underground temperature distribution and spatial suitability assessmentfor geothermal heat pumps in the alluvial fan of the Nagara River, central Japan

A mathematical model and relevant index prediction for constant-temperature electric heating of dual-horizontal-well SAGD start-up

Through Laplace transform and Stehfest numerical inversion, this research established a mathematical model for constant temperature electric heating of dual-horizontal-well steam-assisted gravity drainage (SAGD) start-up. To verify the model, a finite element simulation based on a typical SAGD block was completed, which proved the excellent agreement between the model solution and simulation results. Moreover, by means of superposition principle, underground temperature distribution and energy-related parameters during the multiwell operation were obtained, as well as a computational method targeted at quantifying the conserved energy, water and fuel of electric heating against steam heating. A parametric sensitivity analysis of electric heating was undertaken, which proved that the start-up effect is most sensitive to heating temperature, featuring a nonlinear negative correlation. Additionally, start-up effect is positively linear-correlative to porosity, and negatively linear-correlative to wellbore radius and oil saturation. The proposed model can be employed to predict key indexes such as underground temperature distribution, energy-consumption parameters, and accumulated conserved amounts of energy, water and fuel versus steam heating. Under a specified terminal temperature, temporal and energy quantities required by the start-up can also be determined.

Geothermal potential assessment of the Nevado del Ruiz volcano based on rock thermal conductivity measurements and numerical modeling of heat transfer

This work presents an estimation of the geothermal potential of the Nevado del Ruiz (NDR) volcano, bridging the knowledge gap to develop geothermal energy in Colombia and improve resource estimates in South America. Field work, laboratory measurements, geological interpretations, 2D numerical modeling, and uncertainty analysis were conducted to the northwest of the NDR to assess temperature at depth and define thermal energy content. About 60 rock samples were collected at outcrops to measure thermal conductivity with a needle probe. A 2D numerical model, built from an inferred geological cross-section, was developed with the software OpenGeoSys to simulate the underground temperature distribution and then estimate the geothermal potential of a 1 km2 area with sufficient temperature, assuming a recovery factor equal to 2.4% and a 30 years exploitation time. Coupled groundwater flow and heat transfer were simulated in steady-state considering two different thermal conductivity scenarios. Results show that the average estimated potential is 1.5 × 10−2 MWt m−1 of the reservoir thickness, considering temperatures greater than 150 °C located at a depth of approximately 2 km, in a selected area situated outside of the Los Nevados National Natural Park (NNP), to avoid any direct intervention on this protected area. According to a Monte Carlo analysis considering pessimist and optimist scenarios of thermal conductivity, the estimated geothermal power was 1.54 × 10−2 MW m−1 (σ = 2.91 × 10−3 MW m−1) and 1.88 × 10−2 MW/m (σ = 2.91 × 10−3 MW m−1) for the two modeling scenario considered.

Measurement and modelling of the ground temperature profile in Zarqa, Jordan for geothermal heat pump applications

The use of Geothermal Heat Pumps (GHP) for cooling and heating applications is still to be assessed in Jordan. As a first step in the assessment of the technical and economic feasibility of GHP option, it is necessary to have an accurate understanding of the underground temperature distribution. Such distribution is key to the evaluation of the type, size, design, and depth of the ground heat exchanger of the proposed heat pump systems. For this purpose, this study was conducted to experimentally establish the year-round underground temperature distribution profile near the city of Zarqa in Jordan. The daily and seasonal ground temperature profiles are presented for various depths. It is demonstrated that despite the cyclic nature of the daily and seasonal variations of the ambient and ground surface temperatures, the underground temperature variations diminish with depth and stabilize throughout the year at around 21°C starting from a depth of 5m below the surface. A simplified semi-empirical model was also developed to predict the temperature profile as function of time, depth, the mean ground surface temperature, and soil properties with the help of the measured data.

Time-lapse electrical resistivity imaging of the thermally affected zone of a Borehole Thermal Energy Storage system near Torino (Northern Italy)

A Borehole Thermal Energy Storage living lab was built up nearby Torino (Northern Italy). This living lab aims at testing the ability of the alluvial deposits of the north-western Po Plain to store the thermal energy collected by solar thermal panels and the efficiency of energy storage systems in this climatic context. Different monitoring approaches have been tested and analyzed since the start of the thermal injection in April 2014. Underground temperature monitoring is constantly undertaken by means of several temperature sensors located along the borehole heat exchangers and within the hydraulic circuit. Nevertheless, this can provide only pointwise information about underground temperature distribution. For this reason, a geophysical approach is proposed in order to image the thermally affected zone (TAZ) caused by the heat injection: surface electrical resistivity measurements were carried out with this purpose. In the present paper, results of time-lapse acquisitions during a heating day are reported with the aim of imaging the thermal plume evolution within the subsoil. Resistivity data, calibrated on local temperature measurements, have shown their potentiality in imaging the heated plume of the system and depicting its evolution throughout the day. Different types of data processing were adopted in order to face issues mainly related to a highly urbanized environment. The use of apparent resistivity proved to be in valid agreement with the results of different inversion approaches. The inversion processes did not significantly improve the qualitative and quantitative TAZ imaging in comparison to the pseudo-sections. This suggested the usefulness of apparent resistivity data alone for a rough monitoring of TAZ in this kind of applications.

Analysis of underground cable ampacity considering non-uniform soil temperature distributions

An analytical model for the assessment of cable ampacity due to non-uniform underground temperature distribution is presented. The uneven underground temperature is usually caused by a non-uniform surface heating (e.g., a street or parking crossing, etc.), which is extended for certain length along the cable installation and in depth. The underground temperature distribution is obtained by solving the heat equation with the respective boundary conditions. The cable ampacity reduction is calculated as a function of the surface temperature distribution and the cable depth of burial. The model is validated and several numerical results are obtained for different installation conditions.

Experimental analysis of shallow underground temperature for the assessment of energy efficiency potential of underground wine cellars

Energy saving in production processes is a topical issue in wine sector, where energy demand is mostly due to temperature control. Thus constructive solutions and technological systems that maximize energy efficiency are requested by companies and stakeholders. Underground cellars may represent a solution, as they can provide temperature peaks dampening, thermal wave phase shifting and temperature variation breaking down. The effects depend on building and site features; therefore the knowledge of underground thermal properties and space-time variability of thermal phenomena are fundamental for building design.The objective of the study is to identify time variations of temperature distributions related to ground layers interacting with underground buildings in the wine sector. A monitoring system was implemented and experimental analyses were carried out on two boreholes at different distances from a real underground cellar.Results showed to what extent building design can take advantage of underground thermal properties to minimize energy demand for temperature control. The validity of the standard model of underground temperature distribution was verified for the shallow zone and a procedure was proposed and validated for the assessment of thermal diffusivity. The research represents also a basis for theoretical provisional model definition for surface zones.

년간 지중온도의 실측 및 수치해석에 관한 연구

The geothermal energy is one of the renewable energy sources which can contribute in accomplishing a vision and goal of the national plan on energy for a government suggestion. Especially, the geothermal energy is evaluated as the nearly unlimited resources. The yearly underground temperature distribution by depth is very important to the design of air-conditioning system which uses a geothermal energy. Furthermore, there has no data for comparisons to numerical analysis. In this study, the yearly underground temperature is measured under the depth of 2 m in Tongyeong, and these data are compared with numerical analysis results for checking the accuracy. The results showed that the experimental temperature and numerical results had a good agreements and these results will be utilized to predict a performance of air-conditioning system for using a geothermal energy.

Reconstruction of the thermal environment evolution in urban areas from underground temperature distribution

It is possible to estimate the ground surface temperature (GST) history of the past several hundred years from temperature profiles measured in boreholes because the temporal variation in GST propagates into the subsurface by thermal diffusion. This “geothermal method” of reconstructing GST histories can be applied to studies of thermal environment evolution in urban areas, including the development of “heat islands.” Temperatures in boreholes were logged at 102 sites in Bangkok, Jakarta, Taipei, Seoul and their surrounding areas in 2004 to 2007. The effects of recent surface warming can be recognized in the shapes of most of the obtained temperature profiles. The preliminary results of reconstruction of GST histories through inversion analysis show that GST increased significantly in the last century. Existing temperature profile data for the areas in and around Tokyo and Osaka can also be used to reconstruct GST histories. Because most of these cities are located on alluvial plains in relatively humid areas, it is necessary to use a model with groundwater flow and a layered subsurface structure for reconstruction analysis. Long-term records of subsurface temperatures at multiple depths may demonstrate how the GST variation propagates downward through formations. Time series data provide information on the mechanism of heat transfer (conduction or advection) and the thermal diffusivity. Long-term temperature monitoring has been carried out in a borehole located on the coast of Lake Biwa, Japan. Temperatures at 30 and 40 m below the ground surface were measured for 4 years and 2 years, respectively, with a resolution of 1 mK. The obtained records indicate steady increases at both depths with different rates, which is probably the result of some recent thermal event(s) near the surface. Borehole temperatures have also been monitored at selected sites in Bangkok, Jakarta, and Taiwan.

Ground heat exchanger temperature distribution analysis and experimental verification

The underground two-dimensional symmetry temperature field of a vertical double spiral coil ground heat exchanger (GHX) designed by the authors for a ground source heat pump (GSHP) system was simulated using the volume-control method. A heat transfer model of underground coil is made, and the underground temperature distribution of the coil was solved numerically. Experimental temperature data are measured. The analytical results are compared thoroughly with the experimental data. The mathematical mode presented herein may provide design guidance for the design of GHX for GSHP systems.

50. Underground temperature distribution in central Kyushu considering the effects of the hydrothermal systems(Abstracts of Papers Presented at the Fall Meeting of the Society)

50. Underground temperature distribution in central Kyushu considering the effects of the hydrothermal systems(Abstracts of Papers Presented at the Fall Meeting of the Society)

An Application of the Finite Element Method to the Problem of Underground Temperature Distribution around a Buried Heat Source

An Application of the Finite Element Method to the Problem of Underground Temperature Distribution around a Buried Heat Source

44．Theoretical considerations on underground temperature distribution at Toyoda geothermal field in Hokkaido.

44．Theoretical considerations on underground temperature distribution at Toyoda geothermal field in Hokkaido.