Ground Temperature Variations Research Articles

Soil thermal behavior in different moisture condition: an overview of ITER project from laboratory to field test monitoring

The thermal properties of soils can be considered one of the most important parameters for many engineering projects designing. In detail, the thermal conductivity plays a fundamental role when dimensioning ground heat exchangers, especially very shallow geothermal (VSG) systems, interesting the first 2 m of depth from the ground level. However, the determination of heat transfer in soils is difficult to estimate, because depends on several factors, including, among others, particle size, density, water content, mineralogy composition, ground temperature, organic matter. The performance of a VSG system, as horizontal collectors or special forms, is strongly correlated to the kind of sediment at disposal and suddenly decreases in case of dry-unsaturated conditions in the surrounding soil. Therefore, a better knowledge of the relationship between thermal conductivity and water content is required for understanding the VSG systems behavior in saturated and unsaturated conditions. Key challenge of ITER project, funded by European Union, is to understand how to enhance the heat transfer of the sediments surrounding the pipes, taking into account the interactions between the soil, the horizontal heat exchangers and the surrounding environment. In detail, changes of soil moisture content in the same climatic conditions and under the same thermal stress for five different soil mixtures have been monitored in the ITER test site. The relationship with precipitation and natural/induced ground temperature variations, reaching also water freezing point, are here discussed.

Simulation-based analysis of a ground source heat pump system using super-long flexible heat pipes coupled borehole heat exchanger during heating season

A hybrid ground source heat pump system employing the super-long flexible heat pipes to extract heat from ground is proposed in this work. To evaluate its energy performance and the temperature recovery characteristics near boreholes during space heating season, a comprehensive simulation model was developed considering the dynamic performance of heat pump and the heat transfer of heat pipes and surrounded soil. The results show that the depth of boreholes should be not less 70 m to guarantee a higher long-term energy efficiency. The seasonal coefficient of performance increases with increasing groundwater advection velocity and decreasing building load, with a maximum value up to 4.2 under examined conditions. The short-term variations of ground temperature near boreholes are sensitive to the borehole depth and building load. The overall ground temperature continuously decreases under the condition with no groundwater advection throughout the heating season, but with the presence of groundwater advection, the variation tendency would almost level out after several days of decrease. In addition, it is also revealed that this system has a potential to reduce the ratio of the electrical consumption of circulation pumps to the total consumption, with a reduction of about 7%, showing an advantage of saving energy over the traditional ground-source heat pumps.

A new method for analysing and representing ground temperature variations in cold environments. The Fuegian Andes, Tierra del Fuego, Argentina

The thermal response of soils in cold environments has been investigated in numerous studies. The data considered here were obtained in a study carried out in Tierra del Fuego, Argentina, as part of the IV International Polar Year. Temperature sensors were installed at ground level (0) and depths of -10, -20 and -60 cm in the study area, with the aim of characterizing the thermal response by detecting diurnal and annual variations.The study has two main aims. The first is to present and discuss the study findings regarding the thermal response of a soil in a sub-Antarctic environment by using classical descriptive analysis. The second, closely related, aim is to apply some novel statistical tools that would help improve this description. The study of freeze-thaw patterns can be approached from a non-parametric perspective, while taking into account the cyclical nature of the data. Data are considered cyclical when they can be represented on a unit circle, as with the hours in which certain events occur throughout a day (e.g. freezing and thawing). Analysis of this type of data is very different from the analysis of scalar data, as regards both descriptive and graphical measures. The application in this study of methods used to represent and analyse cyclical data improved visualization of the data and interpretation of the analytical findings. The main contribution of the present study is the use of estimators of the nuclear type density and derived techniques, such as the CircSiZer map, which enabled identification of significant freeze-thaw patterns. In addition, the relationships between the temperature recordings at different points were analysed using Taylor diagrams.

Investigation of the effect of seasonal variation in ground temperature on thermal response tests

Abstract Economical design of Ground Heat Exchangers (GHEs) relies significantly on accurate estimations of ground thermal properties, including undisturbed ground temperature, ground thermal conductivity, and GHE thermal resistance. Typically these are measured in situ by a Thermal Response Test (TRT), where the parameters are back-calculated by fitting a heat transfer model to the temperature response. The accuracy of most models relies on an assumption of constant ground temperature with depth, but in reality there are several mechanisms by which this may be invalid, one being seasonal variation in ground temperature. In this paper a study of Infinite Line Source Model performance under different seasonal conditions using a Finite Element model is presented. The study aims to determine the robustness of interpretation of TRTs conducted at different times of the year and the sensitivity of the effect's key influencing variables. Results suggest that there is little variability in effective thermal conductivity but some variation in GHE thermal resistance. A dimensionless parameter was derived and found to be strongly linearly related to the difference in GHE thermal resistance, leading to generalized estimates of the potential impact on design length that were greater than 10% under relatively extreme conditions and for short GHEs.

Numerical analysis for ground temperature variation

This paper aims to predict ground temperature variation with depth for time variant ambient air temperature and solar radiation data for Jamshedpur, India. Finite difference method has been used to discretise computational domain and a scheme has been employed to determine the numerical solution. The numerical results have been validated with experimental measurement of ground temperature. The diurnal temperature variation for the hottest and the coldest days and annual variation for the year 2016 have been computed. The diurnal temperature variation is found up to 0.4 m depth of soil whereas annual temperature variation is up to a depth of 4 m.

Performance Analysis of Slinky Horizontal Ground Heat Exchangers for a Ground Source Heat Pump System

This paper highlights the thermal performance of reclined (parallel to ground surface) and standing (perpendicular to ground surface) slinky horizontal ground heat exchangers (HGHEs) with different water mass flow rates in the heating mode of continuous and intermittent operations. A copper tube with an outer surface protected with low-density polyethylene was selected as the tube material of the ground heat exchanger. Effects on ground temperature around the reclined slinky HGHE due to heat extraction and the effect of variation of ground temperatures on reclined HGHE performance are discussed. A higher heat exchange rate was experienced in standing HGHE than in reclined HGHE. The standing HGHE was affected by deeper ground temperature and also a greater amount of backfilled sand in standing HGHE (4.20 m3) than reclined HGHE (1.58 m3), which has higher thermal conductivity than site soil. For mass flow rate of 1 L/min with inlet water temperature 7 °C, the 4-day average heat extraction rates increased 45.3% and 127.3%, respectively, when the initial average ground temperatures at 1.5 m depth around reclined HGHE increased from 10.4 °C to 11.7 °C and 10.4 °C to 13.7 °C. In the case of intermittent operation, which boosted the thermal performance, a short time interval of intermittent operation is better than a long time interval of intermittent operation. Furthermore, from the viewpoint of power consumption by the circulating pump, the intermittent operation is more efficient than continuous operation.

Temporal variation of ground temperature at depths 2cm to 200cm in an experimental field in Abeokuta, South-Western, Nigeria

Variation of temperature in the ground with time and depth from the surface is a natural phenomenon which affects most physical and chemical properties of soil. Records of soil temperature were obtained at five depths (2, 50, 100, 150, and 200 cm) below the surface of the earth at Akole, Abeokuta, between 1 January 2014 and 31 December 2014. The soil temperature varied from 27.75 °C at depth 200 cm to 29.9 °C at 2 cm. The diurnal temperature range for depths between 2 and 200 cm during the dry season was higher (about 18 °C) than that during the rainy season (about 12 °C). The temporal variation of ground temperature from the surface at different depths was analyzed by Fourier technique, and thermal diffusivity was computed using amplitude and phase angles of the first three harmonics of the annual thermal wave. The coefficients of soil temperature obtained by Fourier analysis depict the impartial description of the variation with depth of the soil temperature waves. Among the three harmonics calculated, the first harmonic described soil temperature variation to 95.07% while the first two harmonics described the variation to 98.72%. Further harmonics contribute insignificantly to the improvement of the variation. The annual damping depths of the study area calculated from the phase angle and amplitude angle and directly from daily average soil temperatures were 217.39, 227.27, and 217.90 cm, respectively. In the same vein, thermal diffusivity of the study area was found to be 5.1463 × 10−7, 4.708 × 10−7, and 4.7305 × 10−7 m2/s, respectively. The annual amplitude, the mean wavelength, and the phase displacement at the surface were 2.68 cm, 14.0 m, and 31.38 days, respectively.

Long-term plate load tests in permafrost region on the Qinghai-Tibetan Plateau

In order to study the deformation behavior of in-situ warm and ice-rich permafrost with seasonally varying ground temperature, two groups of plate load tests were carried out in permafrost region on the Qinghai-Tibetan Plateau. The test results showed that the deformation of the permafrost under a constant load always represented a stepped pattern due to seasonal variation of ground temperature. Affected by the external load and the variation of the ground temperature, both settlement and frost heave occurred. In the long term, however, settlement was the primary characteristic while frost heave was much slight. The settlement rate was positively correlated with load levels, and was greatly affected by soil temperature as well as ice content in the ground. Regardless of frost heave, the deformation curves of permafrost were well expressed by Burgers viscoelasticity model, and the future settlements can be predicted based on the model.

Factors influencing hydrogen flux in a fault zone of Henan Province, China

This research investigates the main factors influencing changes in hydrogen concentration in a fault zone and analyzes the relationship between hydrogen and tectonic activity. Based on the hydrogen concentration in the fault gas and continuous observation data from Mashankou, Neixiang County, Henan Province, the relationships between the variation in hydrogen concentration and ground temperature, atmospheric temperature, and atmospheric pressure are analyzed. In addition, the earth tide effect on hydrogen in the fault zone is discussed. The results show that the direct influence of atmospheric or ground temperatures on the hydrogen concentration is not significant. The atmospheric and ground temperatures have some impact on the hydrogen concentration only when ground temperature increases. By means of a wavelet analysis method, which separates the semidiurnal wave and diurnal wave signals of hydrogen, the results show that the hydrogen concentration is capable of indicating the solid earth tide when comparing the pressure tide and solid earth tide signals in the same period.

Heat flow and inferred ground surface temperature history at Tynong North, southeastern Australia

ABSTRACTBorehole temperature data have the potential to record historical variations in ground and air surface temperature, yet very few reliable, purpose-drilled, boreholes are available to explore such impacts, particularly in the southern hemisphere. The 400-m deep Tynong-1 borehole, approximately 65 km ESE of Melbourne, Australia, was drilled specifically to determine conductive heat flow and provides a unique dataset for evaluating ground surface temperature history in southeastern Australia. Steady-state conductive heat flow of 87 ± 1 mW m−2 was determined in the deeper borehole sections, with measured temperature profiles clearly demonstrating a progressive divergence of the observed temperature profile from the equilibrium model in the upper ∼150 m of the hole. We applied a Bayesian method employing a reverse jump Markov chain Monte Carlo search algorithm to explore the origins of this variation. Our results indicate a 2°C increase in ground surface temperature since 1800, after at least 500 years of relatively stable ground surface temperature. The inversion results are consistent with the trend of surface air temperature recorded in southeast Victoria by historical meteorological data since 1950. The inferred increase in ground surface temperature evident prior to 1950 is likely a cumulative effect of land clearing and a rise in surface air temperature.

Study the performance of borehole heat exchanger considering layered subsurface based on field investigations

In bedrock geology districts, the stratum in the ground heat exchanger (GHE) borehole varies along the vertical direction. In this paper, the layered subsurface is investigated and the ground temperature variations are studied based on the test systems. Under 60days’ heat injection and 65days’ self-regeneration test in the borehole-#2, the outlet temperature of the analytical homogeneous finite line source (FLS) model is 2.2°C and 1.2°C higher than the tested outlet temperature on at 30th and the 90th day, respectively. The temperature rises at radial distance of 3m, 6m and 9m to the heat injection borehole at depth of 12m, 25m and 80m are recorded and discussed. After 60days’ heating, the temperature rises at radial distance of 3m at depth of 12m, 25m and 80m are 0.82°C, 5.86°C and 3.85°C respectively. A numerical model considering five strata is developed according to the field investigations, and the axial temperature profiles of different layers at different distance under different heating time are presented and explored. It indicates that the layered subsurface and groundwater flow play the non-negligible role on evaluation performance of BHEs.

Experimental and computational investigation of the spiral ground heat exchangers for ground source heat pump applications

This paper investigates the thermal performance of vertical spiral ground heat exchangers (GHEs), experimentally and computationally. Experimental application area consists of nine spiral GHEs and two boreholes with U-Tube GHE. During experimental study, different configurations of spiral GHEs are tested separately for 150h. Ground source heat pump (GSHP) system with nine spiral GHEs operates for 3months intermittently to provide cooling demands of the building in summer. Based on the results of study, thermal performance of the nine spiral GHEs are more accurately analyzed than other configurations. To better investigate thermal behavior of the spiral GHEs, comparative analyses for various configurations of spiral GHEs are explored by using COMSOL software. Based on the validated numerical models, long term heat transfer rate (HTR) of the single and nine spiral GHEs are examined under the most critical working conditions and additionally, for nine spiral GHEs, predictive curve is verified by some actual HTR values. Furthermore, in this study most important designing tools such as, performance losses against time and distance between spiral GHEs, temperature variations in ground, thermal interactions between spiral GHEs and relative performance of spiral GHEs versus different average working fluid temperature are investigated for nine spiral GHEs configuration.

Optimization method for multiple heat source operation including ground source heat pump considering dynamic variation in ground temperature

Recent years have witnessed the widespread use of highly efficient energy systems as an important measure to reduce not only energy consumption but also operating costs. A ground source heat pump system has been attracting considerable attention because of its high efficiency. Although many studies have been conducted to investigate and evaluate the ground source heat pump’s performance, they have not sufficiently studied its optimal operation considering dynamic ground temperature variation caused by the high thermal capacity of the ground. Calculations considering both thermal history of the ground and optimal load dispatch are complicated and thus entail high computation costs. In this paper, an efficient optimization method is proposed to determine optimal operations of a hybrid ground source heat pump system that is used to handle the cooling load and hot water demand. The proposed method, namely epsilon-constrained differential evolution with random jumping, can solve nearly all possible configurations and is a suitable method for the nonlinear configuration used herein because the ground source heat pump has highly nonlinear characteristics and the ground temperature calculation cannot be simplified to a linear formulation. The optimal operations achieved by the proposed method can reduce operating costs by at least 3.78% and at most 12.56% compared to empirical operations. In addition, the proposed method derives the solution rapidly while maintaining high computation accuracy. Therefore, it can be used in practical situations to determine an optimal operating schedule as a day-ahead optimization.

Multicriteria optimization approach to design and operation of district heating supply system over its life cycle

District Heating (DH) systems are commonly supplied using local heat sources. Nowadays, modern insulation materials allow for effective and economically viable heat transportation over long distances (over 20 km). In the paper a method for optimized selection of design and operating parameters of long distance Heat Transportation System (HTS) is proposed. The method allows for evaluation of feasibility and effectivity of heat transportation from the considered heat sources. The optimized selection is formulated as multicriteria decision-making problem. The constraints for this problem include a static HTS model, allowing considerations of system life cycle, time variability and spatial topology. Thereby, variation of heat demand and ground temperature within the DH area, insulation and pipe aging and/or terrain elevation profile are taken into account in the decision-making process. The HTS construction costs, pumping power, and heat losses are considered as objective functions. Inner pipe diameter, insulation thickness, temperatures and pumping stations locations are optimized during the decision-making process. Moreover, the variants of pipe-laying e.g. one pipeline with the larger diameter or two with the smaller might be considered during the optimization. The analyzed optimization problem is multicriteria, hybrid and nonlinear. Because of such problem properties, the genetic solver was applied.

Analysis of ground temperature variations on the basis of years-long measurements

Analysis of ground temperature variations on the basis of years-long measurements

Rock glaciers on the run – understanding rock glacier landform evolution and recent changes from numerical flow modeling

Abstract. Rock glaciers are landforms that form as a result of creeping mountain permafrost which have received considerable attention concerning their dynamical and thermal changes. Observed changes in rock glacier motion on seasonal to decadal timescales have been linked to ground temperature variations and related changes in landform geometries interpreted as signs of degradation due to climate warming. Despite the extensive kinematic and thermal monitoring of these creeping permafrost landforms, our understanding of the controlling factors remains limited and lacks robust quantitative models of rock glacier evolution in relation to their environmental setting. Here, we use a holistic approach to analyze the current and long-term dynamical development of two rock glaciers in the Swiss Alps. Site-specific sedimentation and ice generation rates are linked with an adapted numerical flow model for rock glaciers that couples the process chain from material deposition to rock glacier flow in order to reproduce observed rock glacier geometries and their general dynamics. Modeling experiments exploring the impact of variations in rock glacier temperature and sediment–ice supply show that these forcing processes are not sufficient to explain the currently observed short-term geometrical changes derived from multitemporal digital terrain models at the two different rock glaciers. The modeling also shows that rock glacier thickness is dominantly controlled by slope and rheology while the advance rates are mostly constrained by rates of sediment–ice supply. Furthermore, timescales of dynamical adjustment are found to be strongly linked to creep velocity. Overall, we provide a useful modeling framework for a better understanding of the dynamical response and morphological changes of rock glaciers to changes in external forcing.

Climatic controls on active layer dynamics: Amsler Island, Antarctica

AbstractVariations in atmospheric conditions can be important factors influencing temperature dynamics within the active layer of a soil. Solar radiation and air temperature can directly alter ground surface temperatures, while variations in wind and precipitation can control how quickly heat is carried through soil pores. The presence of seasonal snow cover can also create a thermal barrier between the atmosphere and ground surface. This study examines the relation between atmospheric conditions and ground temperature variations on a deglaciated island along the Western Antarctic Peninsula. Ground temperatures were most significantly influenced by incoming solar radiation, followed by air temperature variations. When winter months were included in the comparison, the influence of air temperature increased while solar radiation became less influential, indicating that snow cover reflected solar radiation inputs, but was not thick enough to insulate the ground. When ground temperatures were compared to atmospheric conditions of preceding weeks, seasonal temperature peaks 1.6 m below ground were best related to seasonal air temperature peaks from the previous two weeks. The same ground temperature peaks were best related to seasonal solar radiation peaks of seven weeks prior. This difference was a result of temperature lags within the atmosphere.

Long term behavior of a geothermal heat pump with oversized horizontal collector

This study presents the results of a 3year experiment concerning the behavior of a geothermal ground-water heat pump used for heating a small residential house. The study is focused on the one side on the ground temperature variation around the horizontal collector oversized by ≈50%, mounted at 1.7m depth and on the other side on the working conditions and performances of the heat pump itself. It was highlighted that due to the oversizing of the geothermal collector, the ground temperature did not drop below 2°C and ground freezing was avoided. The ground temperature recovered each year during the non-heating season. The heat pump coefficient of performance was determined in the range of (3.18–8.59) in different operating periods.

지하수류가 밀폐형 천공 지중열교환기 성능에 미치는 영향(1)

To analyze the influence of various groundwater flow rates (specific discharge) on BHE system with balanced and unbalanced energy loads under assuming same initial temperature (15℃) of ground and groundwater, numerical modeling using FEFLOW was used for this study. When groundwater flow is increased from 1 × 10^−7 to 4 × 10^−7m/s under balanced energy load, the performance of BHE system is improved about 26.7% in summer and 22.7% at winter time in a single BHE case as well as about 12.0~18.6% in summer and 7.6~8.7% in winter time depending on the number of boreholes in the grid, their array type, and bore hole separation in multiple BHE system case. In other words, the performance of BHE system is improved due to lower avT in summer and higher avT in winter time when groundwater flow becomes larger. On the contrary it is decreased owing to higher avT in summer and lower avT in winter time when the numbers of BHEs in an array are increased, Geothermal plume created at down-gradient area by groundwater flow is relatively small in balanced load condition while quite large in unbalanced load condition. Groundwater flow enhances in general the thermal efficiency by transferring heat away from the BHEs. Therefore it is highly required to obtain and to use adequate informations on hydrogeologic characterristics (K, S, hydraulic gradient, seasonal variation of groundwater temperature and water level) along with integrating groundwater flow and also hydrogeothermal properties (thermal conductivity, seasonal variation of ground temperatures etc.) of the relevant area for achieving the optimal design of BHE system.

Small-scale variation of snow in a regional permafrost model

Abstract. The strong winds prevalent in high altitude and arctic environments heavily redistribute the snow cover, causing a small-scale pattern of highly variable snow depths. This has profound implications for the ground thermal regime, resulting in highly variable near-surface ground temperatures on the metre scale. Due to asymmetric snow distributions combined with the nonlinear insulating effect of snow, the spatial average ground temperature in a 1 km2 area cannot be determined based on the average snow cover for that area. Land surface or permafrost models employing a coarsely classified average snow depth will therefore not yield a realistic representation of ground temperatures. In this study we employ statistically derived snow distributions within 1 km2 grid cells as input to a regional permafrost model in order to represent sub-grid variability of ground temperatures. This improves the representation of both the average and the total range of ground temperatures. The model reproduces observed sub-grid ground temperature variations of up to 6 °C, and 98 % of borehole observations match the modelled temperature range. The mean modelled temperature of the grid cell reproduces the observations with an accuracy of 1.5 °C or better. The observed sub-grid variations in ground surface temperatures from two field sites are very well reproduced, with estimated fractions of sub-zero mean annual ground surface temperatures within ±10 %. We also find that snow distributions within areas of 1 km2 in Norwegian mountain environments are closer to a gamma than to a lognormal theoretical distribution. The modelled permafrost distribution seems to be more sensitive to the choice of distribution function than to the fine-tuning of the coefficient of variation. When incorporating the small-scale variation of snow, the modelled total permafrost area of mainland Norway is nearly twice as large compared to the area obtained with grid-cell average snow depths without a sub-grid approach.