No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Vertical distribution of shallow ground thermal properties in different geological settings in Croatia
... DTSs are installed in a BHE to measure continuous depth-resolved temperature measurements during the heating phase, as called distributed TRT (DTRT). DTRT is classified in terms of installation number and location of DTSs; (1) a single DTS outside U-tubes [24], (2) a looped DTS attached along U-tubes [25], (3) a DTS into an inlet or outlet U-tube [13], and (4) a pair of DTS into inlet and outlet U-tubes [26,27]. Instead of circulating fluids at constant heating, the electric current-carrying copper wire is also used as a heat source along the DTSs [28][29][30]. ...
... The studies above have demonstrated to estimate vertical profiles of ground thermal conductivity from the distributed temperature data. A part of the studies also analyzed the profiles of borehole thermal resistance [26]. The heating cable TRTs were available in the boreholes at geotechnical investigations to cut the drilling costs [31]. ...
The variability of ground thermal conductivity, based on underground conditions, is often ignored during the design of ground-source heat pump systems. This study shows a field evidence of such site-scale variations through thermal response tests in eight borehole heat exchangers aligned at a site on a terrace along the foothills of mountains in northern Japan. Conventional analysis of the overall ground thermal conductivity along the total installation length finds that the value at one borehole heat exchanger is 2.5 times that at the other seven boreholes. History matching analysis of underground distributed temperature measurements generates vertical partial ground thermal conductivity data for four depth layers. Based on the moving line heat source theory, the partial values are generally within a narrow range expected for gravel deposits. Darcy velocities of groundwater are estimated to be 74-204 m/y at the borehole with high conductivity, increasing in the shallow layers above a depth of 41 m. In contrast, the velocities at the other seven boreholes are one-to-two orders of magnitude smaller with no trend. These high and low velocity values are considered for the topography and permeability. However, the relatively slow groundwater velocities might not apparently increase the partial conductivity.
... ETRT better fulfil this assumption due to a constant heat load supplied by the heating wire. The second possibility is to divide the subsurface into sections and calculate q for each section based on the temperature difference (ΔT) between the start and end points of every section [39,42,69,74]: ...
... In contrast, Soldo et al. (2015) obtained a R b value only 2.3% lower when using optical fiber cables installed inside the pipes of a 100 m BHE (Table 2) [40,69]. Variations of averaged R b between 0.055 and 0.154 mK/W were found by for the same test setup installed on eight different locations spread over Croatia [74]. No detailed statement was given regarding the variations, yet the highest value was explained with an inappropriate grouting process. ...
In this study, the historical and technical development and the current status of distributed (DTRT) and enhanced
(ETRT) thermal response tests (TRT) are reviewed. The different test setups of these advanced TRT are critically
assessed and future research questions are outlined. Advanced TRT use specific temperature measurement
techniques for the depth-resolved determination of site-specific ground parameters that are required for an
optimal design of borehole heat exchanger (BHE) fields. The depth-resolved determination of these thermal
properties, such as effective thermal conductivities and thermal borehole resistances, is the key advantage in
comparison to conventional TRT, promising economic benefits during the installation and operating phase of
ground source heat pump (GSHP) systems. Various test setups exist which differ regarding the heating procedure,
i.e. circulating heating fluid and heating wire, the temperature measurement technique, i.e. optical fiber and
wireless probe, as well as in their suitability for parameter estimation. These advanced techniques can
furthermore provide information about geological layers, fractured zones and groundwater influenced sections in
the subsurface as well as inadequate backfilled zones along the borehole heat exchanger. Despite this, advanced
TRT are reported in international literature only for a few locations and some test setups are purely theoretical
without any practical demonstration. Uncertainties exist regarding the comparability of the test setups, the
sensitivity of the measurement devices under test conditions, as well as the best evaluation procedure. Also,
scarce information is available about the use beyond academic field and economic aspects in comparison to
conventional TRT. Encouraging further research and a more extensive transfer of these promising techniques
from academia to practice is therefore also the aim of this review.
... In natural scale, the thermal response test (TRT) and distributed TRT (DTRT)-using advanced distributed temperature sensing by fibre optic cables-were conducted. The results of thermal response testing have been published in a previous paper (Soldo et al. 2016). Direct measurements on core samples were conducted by ISOMET 2114 equipment, using predominantly surface probe (for rocks), but also the needle probe for partially solidified samples. ...
... Concerning GSHPs, the collected data show that laboratory measurements systematically overestimated ground thermal conductivity in karst terrains in general, but underestimated it in the areas of high groundwater flow from the hinterland through karst conduits, i.e., thermal properties of rock mass do not correspond well to thermal properties of carbonate rock as a monolith. DTRT has proven to be an excellent indicator of natural scale thermal properties of karstified rock mass and, additionally, of karst phenomena such as highly karstified fault and fracture zones-preferential paths of groundwater flow, where heat is transferred by advection, not only by conduction in the solid matter (Soldo et al. 2016). In addition, the unpredictability of drilling and heat exchanger installation in karst terrain was confirmed, and attributed to subsurface geological properties. ...
Hydrogeological and thermogeological properties of the shallow subsurface in the Dinaric karst area of Croatia were investigated in the context of its utilization for ground- and water-source heat pumps (GSHPs and WSHPs). The research encompassed four 100 m deep boreholes with GSHP installations in both coastal and inland Dinaric karst (different limestones and evaporitic rocks at one location), and a set of six exploratory boreholes, abstraction and reinjection wells for WSHP heating and cooling using seawater on the coast (fractured and karstified limestones). It was determined that rock thermal conductivities are favourable for GSHP utilization, but dependent on the wider rock mass characteristics which are hard to predict (size of karst voids and their saturation status). In addition, wells with high enough yield and stabile seawater or groundwater temperatures for WSHP utilization can be designed in appropriate structural settings (tensional fractures and fracture set intersections). Advantages and disadvantages of the utilized methodology have been pointed out, as well as methods which should prove useful in the future, especially if larger systems are planned. Hydrogeological, geotechnical, and thermal risks expected during the drilling, installation, and operational phases have also been identified. Presented case studies have given the insight into heat pump installation options and conditions in Croatian part of the Dinarides, but can be useful to other researchers and engineers both in the Dinarides and in similar karst regions.
... Compared to the other Renewable Energy Sources (RES), SGE employs more uncertainties regarding the high impact of the local and site conditions. Parameters like geology [4,5], soil properties [6], hydrogeological properties [7], climate [5,8,9], and weather [10] are amongst the most studied ones. Energy output differs in favour of regions with higher needs for heating and cooling compared to the ambient temperatures. ...
... Compared to the other Renewable Energy Sources (RES), SGE employs more uncertainties regarding the high impact of the local and site conditions. Parameters like geology [4,5], soil properties [6], hydrogeological properties [7], climate [5,8,9], and weather [10] are amongst the most studied ones. Energy output differs in favour of regions with higher needs for heating and cooling compared to the ambient temperatures. ...
The design and operation of Shallow Geothermal Energy (SGE) systems have been continuously increasing in scientific research over the past years. What hinders the wide penetration of SGE systems in most countries are issues mostly related to high installation costs, administration, stakeholders’ awareness, and marketing. On top of this, SGE systems lack an in-depth economic evaluation, which is often limited to the financial inputs, and thus omitting the non-market monetized environmental benefits. This paper consists of a primer for conceptually improving understanding in regions with low levels of SGE penetration. It provides guidance to project evaluation and discusses the social and institutional strategies to assist SGE systems penetration.
... Below 12.5 m depth, the ground temperature did not change with seasons. The average temperature at 12. The ground temperature along the depth of the borehole for different locations were presented in Ref. [17,18,19]. The ground temperature along the depth of the borehole can be divided into two regions. ...
... Second, thermostatic zone in the deeper ground (12.5100 m). The zone where the ground temperature was almost constant varies from c. 8 o C (as it can be seen in Bialystok, Fig. 3), about 11-12 o C in Wroclaw (Poland) [17], from 10.5 o C to 16.5 o C in Croatia [18] and c. 20 o C in Chongqing of China [19]. ...
The paper presents the ground temperature analysis, heat flows and energy transferred from the soil massif by the vertical ground heat exchangers (VGHE). Three cases – with one, two and three vertical heat exchangers were compared. Their influences on the soil massif temperature in the heat exchangers area were shown. The mass flow and the temperature at the inlet and outlet side of the heat pump were measured in each circuit. Additional, the electricity consumption by the heat pump and energy supply to buffer vessel were measured. Finally, the Coefficient of Performance (COP) as a function of length of VGHE is shown for selected interval time.
... First applications tested the use of DTRT in different kinds of heat exchangers (HEs), such as in both the supply and return leg of a single-U loop (Fujii et al. 2009) or within both a coaxial and standard single-U loop (Acuña and Palm 2013), to study the effects of pipe configuration. Other applications applied fiber optic distributed temperature measurements to monitor longterm effects or execute DTRTs or ETRTs to analyze local ground thermal properties in different conditions of groundwater flows and heterogeneous lithology (Soldo et al. 2016;McDaniel et al. 2018;Herrera et al. 2018), also combining the results with laboratory thermophysical measurements of cores and traditional TRT outputs. ...
In this work, an hybrid cable was grouted into a 125-m well located in the Po Plain in Northern Italy. The provided core defined the geological environment as a continuous succession of unconsolidated alluvial deposits of very limited thickness, grouped in 15 different granulometric units. Three enhanced thermal response test (ETRT) data sets were acquired in different seasons; for 5 days of heating followed by 5 days of recovery, the soil temperature was recorded continuously along the well, with a spatial resolution of 1 m. A new approach using a multiple linear regression is proposed to analyze the data sets to achieve the Thermal Conductivity of the 15 identified granulometric units..
... Meanwhile, the measurement of undisturbed and disturbed T-logs in BHEs is mostly carried out over the course of distributed and enhanced thermal response tests (DTRT/ETRT) (Wilke et al., 2019). This is based on distributed temperature sensing (DTS) using fiber optic and hybrid cables (Acuña et al., 2009;Cao et al., 2018;Fujii et al., 2009;Luo et al., 2015;Shim and Song, 2011;Soldo et al., 2016). Alternative devices to fiber optic cables are wired data loggers, which are either manually (Gehlin and Nordell, 2003) or automatically (Aranzabal et al., 2019a(Aranzabal et al., , 2020 lowered into a BHE. ...
The reliability of temperature measurements in open and closed geothermal systems is closely related to their design, quality control and performance evaluation. Thus, wireless and miniaturized probes, which provide highly resolved temperature profiles in borehole heat exchangers (BHEs), experience a growing interest in research. To ensure quality assurance and reliability of these emerging technologies, errors and uncertainties relating to wireless temperature measurements (WTMs) must be determined. Thus, we provide a laboratory analysis of random, systematic and dynamic measurement errors, which lead to the measurement uncertainties of WTMs. For the first time, we subsequently transfer the calculated uncertainties to temperature profiles of the undisturbed ground measured at a BHE site in Karlsruhe, Germany. The resulting precision of 0.011 K and accuracy of -0.11 K ensure a high reliability of the WTMs. The largest uncertainty is obtained within the first five meters of descent and results from the thermal time constant of 4 s. The fast and convenient measurement procedure results in substantial advantages over Distributed Temperature Sensing (DTS) measurements using fiber optics, whose recorded temperature profiles at the site serve as qualitative comparison. We additionally provide recommendations for technical implementations of future measurement probes. Our work will contribute to an improved understanding and further development of WTMs.
... A numerical algorithm is processed based on the line source equation (Ingersoll and Plass, 1948) and an optimization solver (least-squares parameter estimation) calculates depth-specific effective values of λ and R b . Fiber optics have become a valuable tool for obtaining the distributed temperature along the length of BHE with more research activities reported in the recent years (Hakala et al., 2014;Soldo et al., 2016;Luo et al., 2015;Radioti et al., 2016;Monzó, 2018). (Raymond and Lamarche, 2014;Raymond et al., 2015) elaborated an approach to implement a distributed TRT by reducing the electrical energy consumption needed to heat the BHE in comparison with the standard TRT. ...
Standard thermal response tests (TRT) are typically carried out to evaluate subsurface thermal parameters for the design and performance evaluation of borehole heat exchangers (BHE). Typical interpretation methods apply analytical or numerical solutions, which assume that the ground is homogeneous, isotropic and infinite. However in reality, the underground is commonly stratified and heterogeneous, and therefore thermal properties might significantly vary with depth. Thus, novel instruments and methods are necessary to characterize thermo-physical properties along the BHE. In this study, two novel in-borehole temperature measurement instruments, Geoball and Geowire, are assessed during the performance of a distributed TRT (DTRT). The latter is evaluated in comparison to the widely used fiber optical thermometers. Our results suggest that both novel instruments have several advantages. For instance, both devices are able to instantaneously measure temperature with a higher spatial resolution. In addition, our study evaluates two methods to estimate depth-specific thermal conductivities: (1) a computer program based on infinite line source (ILS) approach and (2) a recently suggested inverse numerical procedure. For the latter less data is required, while demonstrating an accurate resolution to even detect thin conductive geological layers. Moreover, the average value of the depth-specific local effective estimates for both methods is significantly close to the effective subsurface conductivity of 3.20 W/m-K calculated based on standard TRT: 1.27 % below for the computer program and 0.28 % below for the numerical procedure.
... Such configuration enables distributed temperature measurements along the depth of the borehole. In other studies authors used fiber optic cables placed inside the U-pipe [13], based on works of Acuna [2] and Fujii [14]. ...
... Use of soil as a heat source for a GHP that works in both heating and cooling mode is presented in [6]. Therein, experimental data are given for measured temperatures through the depth of the Borehole Heat Exchanger (BHE), at the beginning of operation and after a certain time of GHP operation. ...
The aim of the paper is to examine the possibility of application of the spreadsheet calculator and Reference Fluid Thermodynamic and Transport Properties database to a thermodynamic process. The heating process of a real soil-to-water heat pump, including heat transfer in the borehole heat exchanger has been analysed. How the changes of condensing temperature, at constant evaporating temperature, influence the following: heating capacity, compressor effective power, heat supplied to evaporator, compression discharge temperature and coefficient of performance, are investigated. Also, the energy characteristics of a heat pump using different refrigerants for the same heating capacity and the same temperature regime are compared. The following refrigerants are considered: two zeotropic mixtures, R407C and R409A, a mixture with some zeotropic characteristics, R410A, and an azeotropic mixture, R507A. © 2018, International Centre for Sustainable Development of Energy, Water and Environment Systems SDEWES. All rights reserved.
... Kallio and Radioti et al. [26,27] obtained temperature profiles of bedrock via DTS and then investigated bedrock heterogeneity. Soldo et al. [28] carried out DTS based TRTs in eight boreholes to compare the thermal conductivity of two geologically different regions. Besides measuring vertical thermal conductivity distribution, the other two significant applications of DTS in TRTs are measuring the undistributed temperature profile and groundwater flow [29][30][31][32] . ...
In-situ thermal response testing (TRT) has become the most effective way to determine ground thermal parameters before developing renewable geothermal energy systems. However, these parameters may not be static when some hydrologic conditions in porous formation change with time. In this paper, we propose a method for evaluating the ground heat exchange performance using the active distributed temperature sensing (A–DTS) technology, which infers soil moisture by a thermal response caused by active electrical current. We evaluated the feasibility of this method by several lab experiments and a field thermal response test (TRT). Using this method, the relationship between thermal conductivity and soil moisture content was established for silt, clay, organic soil and sand, respectively. To quantitatively evaluate the sensitivity of soil thermal conductivity to moisture content, a new parameter called relative thermal conductivity (β), is defined to describe the effect of water bridges among soil solid particles on thermal conductivity. The lab test results demonstrate that soil moisture content has significant influence on thermal conductivity when the soil is nearly dry (β > β(cri)), but its effect becomes less evident when the soil is moist (β ≤ β(cri)). It is found that the relationship between soil moisture content and thermal conductivity can be well fitted by the Johansen model. The results of the field-scale TRT demonstrated the ability of the proposed technique to detect the effects of rainfall on soil thermal conductivity near the ground surface. The field test results also suggest that the soil thermal conductivity measured by in-situ DTS is larger than that obtained from soil samples in lab. However, for rock, the thermal conductivity acquired by DTS is less than the values collected in lab.
... Ground source heat pumps (GSHPs) are a rapidly growing use of geothermal energy (Soldo et al., 2016), accounting for 70% of the installed capacity and 55% of the total direct use of geothermal energy in 2015 (Lund and Boyd, 2015). GSHP systems are highly efficient technologies that meet the heating and cooling demands of houses and buildings while preserving fossil fuels and avoiding additional CO 2 emissions (Molina-Giraldo et al., 2011). ...
Ground source heat pump (GSHP) systems are serving the heating and cooling demands of buildings worldwide. However, the widespread usage of these systems is limited because of their higher initial costs compared with conventional heating and cooling systems, especially in countries with high drilling costs like Japan. The semi-open loop GSHP system was introduced by authors and the results of heating tests and numerical modeling have been published. This system comprises two ungrouted vertical Ground heat exchangers (GHEs) in which groundwater is pumped from one well and injected to another using a water pump. The purpose of the water pumping and injection is to create an artificial groundwater flow around the GHEs to increase the heat advection between the GHEs and the surrounding environment.
In this study, cooling tests on the semi-open loop GSHP system were performed and the thermal performance of the system was measured in each test. The developed numerical model was validated using the results of the cooling tests. Then, a sensitivity analysis was performed to evaluate the system performance under different operational and geological conditions during cooling operation. The results showed that in comparison with conventional GSHP operation, cooling coefficient of performance (COP) and system coefficient of performance (COPsys) can be enhanced by 13.1% and 6.6%, respectively, under fast groundwater flow conditions, as expected at the experimental site. In the absence of groundwater flow, the semi-open loop system is estimated to boost the cooling COP and COPsys by 101% and 62%, respectively, for cooling operations. Finally, an economic analysis was performed, considering the capital and running costs of the system and also the additional equipment costs associated with semi-open loop systems. The results of the economic analysis showed that water pumping and injection can reduce GSHP system costs by 22–36%.
... Based on the results, the thermal properties and UGT for 10 target locations were presented. Soldo et al. [29] developed a distributed TRT method that advanced the existing TRT, which can estimate underground thermal properties (i.e., ground thermal conductivity) using UGT data obtained through a fiber-optic cable. ...
Over the last 37 years, particular interest has been directed towards exploring the characteristics of the optical environment for sensing, giving rise to what would now be one of the largest applications of well-known optical fibers, typically employed to transmit data at high rates. Sensing temperature, pressure, liquid level, deformation, and other physical parameters utilizing optical fibers has become a growing branch of research and a business competing with well-established electrical sensors in the industry. Optical fiber sensors have all the inherent characteristics of a fiber optic cable, such as electromagnetic immunity, small size and weight, multiplexing, and so on. These exclusive features have made fiber sensors so versatile as to become a transformative technology by enabling several industrial processes to be carried out with higher reliability. Nowadays, there are several optical sensors, including fiber Bragg grating, interferometric, polarimetric, polymer fiber, distributed, and several others. Specifically, Raman-based distributed temperature sensor (RDTS) is a class of fiber optic sensors broadly employed in temperature measurement of large structures such as oil and gas wells, tunnels, and pipelines. Since 1985, many techniques have been proposed to break through the barriers of exploring Raman scattering as a distributed temperature measurement method. Range, spatial and temperature resolutions have been the most investigated parameters. In this perspective, this paper presents a comprehensive review focused on the progress of the RDTS technology over the past 37 years (1985–2022), covering an analysis of over 500 journal papers. First, a brief introduction to fiber optic sensor technology is presented as a theoretical basis, discussing the emergence of distributed sensors. Subsequently, Raman scattering in optical fibers is introduced, as well as how this nonlinear effect can be used to build temperature sensors. Next, RDTS technology is detailed, followed by a discussion of its applications and evolution over nearly four decades of development. Lastly, future perspectives are addressed in this review for the advancements in distributed temperature sensor technologies.
Estimation of ground thermal conductivity plays an important role in design of borehole heat exchanger (BHE) for ground source heat pump (GSHP) systems, and the ground is usually heterogeneous with layered thermal properties. Therefore, this study presented a novel estimation method for layered ground thermal conductivity by using distributed thermal response test (DTRT) and genetic algorithm. Firstly, a comprehensive new 2-D heat transfer model for coaxial BHE was built to simulate borehole fluid temperature profiles, it revealed that the distribution of ground thermal conductivity showed a significant influence on outlet temperature and temperature profiles. Then, based on the built model, the vertical distribution of ground thermal conductivity was estimated through DTRT data by using the genetic algorithm. It was found that the DTRT data at 2h was effective to estimate the layered ground thermal conductivity by using the new 2-D heat transfer model. Furthermore, the estimated distribution of ground thermal conductivity was almost independent of numbers or thickness of sub-layer, and the largest difference in distributions of ground thermal conductivity among different layer thickness was less than 0.3W/(m·K). Also, the estimation convergence showed independence with layer thickness, converged results could be obtained after 10 iterations for different layer conditions.
The thermal response test (TRT) is widely used as a standard test to characterize the thermal properties of the ground near a borehole heat exchanger (BHE). Typical methods to interpret the results apply analytical or numerical solutions which assume that the ground is infinite, homogeneous and isotropic. However, in reality the underground is commonly stratified and heterogeneous, and therefore thermal properties may significantly vary with depth. In this sense and with the intention to overcome standard TRT limitations, this Ph.D. study is focused on developing methods and instruments for the evaluation of the heat transfer behavior of the geological layers surrounding a BHE. This information is key for the optimal energy efficiency and techno-economic sizing of BHE.
In particular, a novel TRT method, called observer pipe TRT (OP-TRT), is proposed based on an additional temperature measurement along an auxiliary pipe. In the last decades, some researchers developed the so-called distributed TRT (DTRT) by measuring the temperature along the length of the heated U-pipe. However, from the studies carried out in this Ph.D. work, the observer pipe demonstrated to amplify the thermal effects produced due to geological layers with different thermo-physical properties, hence requiring less accurate sensors for obtaining more detailed results. Based on this achievement, an inverse numerical solution was developed to parametrize thermal conductivity of geological layers from the measurements along the observer pipe. Basically, the model adjusts thermal conductivity of the geological layers until simulation results fit experimental temperature profile along the observer pipe. The model was developed with a parameter estimation solver for an automatic fitting and more accurate results. Another advantage is that this method only requires two temperature profiles: (1) undisturbed ground (before the TRT) and (2) at the end of the TRT (before stopping the heat injection).
In order to further investigate the proposed method by using higher quality data, a specific instrument (Geowire) was developed to automatically measure the required depth-temperature profiles with high accuracy. The design of the Geowire also coveredother features, such as compatibility with TRT equipment and intuitive operation. In addition, an enhanced version of a flowing probe (Geoball) was developed, suitable for both vertical and horizontal pipe arrangements. After laboratory validation tests, the key features of both instruments were evaluated in comparison with new and standard in-borehole instruments for temperature measurements in a test BHE. The main advantage of the proposed instruments over the widespread fiber optics is that they measure the temperature instantaneously (for precise time instants). Moreover, they do not require a dynamic calibration for accurate results while providing higher spatial and temperature resolutions: Geowire (0.5 mm, 0.06 K) and Geoball (10 mm, 0.05 K). Also, they are easier to integrate in existing boreholes and are a potentially more cost-effective solution to measure the distribute temperature.
Finally, the benefits of the proposed method and instruments are demonstrated throughout a DTRT in comparison with fiber optics and with a computer program based on the infinite line source model to estimate the distributed thermal conductivity. The results from the proposed model revealed a highly conductive zone when using data from the Geowire, whereas this was not the case when data from fiber optics were processed.
Seasonal performance of a heat pump in heterogeneous ground is investigated using a resistance-capacity model. Heat pump and borehole heat exchanger models are based on the existing ground-coupled heat pump system. Simulation results show that the application of average undisturbed ground temperature instead of a ground temperature profile has no effect on the obtained seasonal values of the coefficient of performance (COP). On the other hand, a different orientation of the ground thermal conductivity affects the seasonal coefficient of performance. The highest seasonal COP value of 4.86 is found in the case of a homogenous distribution of thermal conductivity while the largest drop in the COP value is observed in the ground profile with the thermal conductivity which steeply increases with depth. The difference between the two cases of 3% in the cooling season and 1% in the heating season is much smaller than the differences reported in previous studies where internal borehole heat transfer is not accounted for. Small relative difference indicate that the homogenous ground approach slightly overestimates the heat pump performance in a purely conductive underground.
Free access until July 20, 2019: https://authors.elsevier.com/a/1Z8g03QJ-dbKM9. The standard thermal response tests (TRT) provide integral and effective thermal parameters of the ground in the vicinity of borehole heat exchangers (BHE). However, typical ground properties are heterogeneously distributed. As a result, advanced TRT such as distributed and enhanced TRT are growing in popularity as they provide more spatial information of the thermal properties. Thus, the objective of this study is to compare various instruments to measure the depth-dependent temperatures using standard Pt100-sensors, fiber optical thermometers and novel instruments such as Geowire, Geoball and GEOsniff®. The investigations are carried out in a 30 m length test borehole. The results showed an excellent agreement between both the Geowire and GEOsniff® in comparison with Pt100-sensors with a root mean squared error of 0.10 and 0.09 K, respectively. The results also suggest that the novel instruments have various advantages over the standard sensors and fiber optics. For example, with the novel instruments comparable, accurate, inexpensive, instantaneous and higher spatial resolution temperature measurements are obtained. Finally, the outcome of this study provides a guide for choosing the adequate temperature measurement along a BHE thus generally improving the evaluation of advanced TRT, while potentially increasing efficiency and economic viability of ground-source heat pump systems.
This paper proposed a parameter estimation method for identifying ground thermal conductivity and volumetric heat capacity using the Nelder-Mead Simplex search algorithm (NMSA) in in-situ thermal response test (TRT) with unstable heat rate, the duct storage system (DST) model for borehole heat exchanger (BHE) was applied to do with variable heat rate and the vertical ground temperature distribution in initial soil temperature. The parameter estimation was carried out using the in-situ TRT data in Qingdao, and the effect of vertical ground temperature distribution on estimated results was compared and analyzed. The relative error of estimated ground thermal conductivity using the regression temperature fitted by the test temperatures from the 5 th m depth to the 120 th m depth decreased by about 9.1% than that corresponding to the integral mean temperature calculated by test temperatures from the 5 th m depth to the 120 th m depth. However, the estimated volumetric heat capacity is hardly sensitive to initial soil temperature, and the relative errors are not higher than 2% no matter how to do with initial soil temperature.
Thermogeological and hydrogeological properties of the shallow subsurface in the Croatian part of the Pannonian Basin System (PBS) were investigated in the context of its utilization for ground source heat pump (GSHP) system installations. Detailed borehole core determinations, sampling and thermal conductivity measurements were conducted for seven boreholes at four locations in diverse geological settings. The results of 418 measurements conducted on 82 sediment and rock samples were compiled and analysed in the context of existing collections of thermal conductivities from Germany and Switzerland which are frequently utilized for borehole heat exchanger (BHE) dimensioning in other countries. Discrepancies have been detected between thermal conductivity data from different geographical regions and geological settings. These results imply that local data sets should be further developed to enable accurate BHE sizing. In four boreholes, thermal response tests (TRTs) were also conducted, and the results were therefore compared with direct measurements on samples. The comparison demonstrated that in environments with significant groundwater flow (coarser-grained sediments) the laboratory measurements systematically underestimated the values of natural-scale thermal conductivity, while the discrepancies were low in finer-grained sedimentary environments. Consequently, TRTs are recommended for all installations in the presence of significant groundwater flow, while at locations with low flow velocity, the analogy to values cited in data collections can be used for small-scale installations. It is important to have a collection of measurements for local geological substances in cases when thermal response testing would not be economically feasible. The values reported in this paper can be a guideline for proper GSHP system dimensioning in order to achieve better performance, especially of small-scale systems in Croatia and other geologically comparable localities in the PBS area.
The utilization of shallow geothermal energy is well known in several European countries. Even though large parts of the Republic of Croatia show significant potential for its use, the installation of ground source heat pump systems (heat pump and heat exchangers) is slowly progressing. Therefore, a short overview of research published thus far concerning the utilization and assessments of shallow geothermal potential for Croatia was done. In Croatia, there is no agency or government department in charge of collecting and publishing data concerning installations of heat exchangers. Therefore, a study was done to collect the available data on installed closed-loop heat exchangers either from scientific research or from personal contacts with drilling companies. Based on the collected data, a map was produced that shows general locations of installed heat exchangers. From the obtained data of installed heat exchanger length, a first assessment of utilizing shallow geothermal potential in Croatia was given.
The thermal response test (TRT) is the standard method for characterizing the thermal properties of the ground and those of a borehole heat exchanger (BHE). During the TRT, the inlet and outlet temperatures of the BHE are monitored. However, this test typically considers the ground as a homogeneous, isotropic, and infinite media, and therefore, it only determines the bulk and effective parameters, such as effective thermal conductivity and thermal borehole resistance. Hence, the enhanced TRT protocols are necessary where the depth-dependent temperatures are measured to estimate depth-specific thermal properties. Thus, a novel instrument with a data logger to automatically obtain the temperature measurements along the BHE is introduced. This device is based on a Zynq-7000 all programmable system on a chip. It has a dual-core central processing unit and a field-programmable gate array on one chip, thus providing a versatile architecture that reduces cost and improves efficiency in comparison with other systems of similar characteristics. This paper describes the implemented hardware and software developments that range from user interface application to a free-distribution operating system based on an embedded Linux. The proposed instrument can be easily incorporated throughout a TRT, and the nonspecialized staff can remotely manage or visualize the results through a menu-driven interface. The device is tested in a specific BHE installation and validated with standard Pt100-temperature-sensors. The results are comparable and, therefore, demonstrate the applicability of this novel instrument called Geowire.
This paper presents a review of the worldwide applications of geothermal energy for direct utilization, and updates the previous survey carried out in 2010. We also compare data from 1995, 2000 and 2005 presented at World Geothermal Congresses in Italy, Japan and Turkey, respectively (WGC95, WGC2000, and WGC2005). As in previous reports, an effort is made to quantify ground-source (geothermal) heat pump data. The present report is based on country update papers received from 70 countries and regions of which 65 reported some direct utilization of geothermal energy. Seventeen additional countries were added to the list based on other sources of information. Thus, direct utilization of geothermal energy in a total of 82 countries is an increase from the 78 reported in 2010, 72 reported in 2005, 58 reported in 2000, and 28 reported in 1995. An estimation of the installed thermal power for direct utilization at the end of 2014 is used in this paper and equals 70,885 MWt, 46.2% increase over the 2010 data, growing at a compound rate of 7.9% annually with a capacity factor of 0.265. The thermal energy used is 592,638TJ/year (164,635 GWh/year), about a 39.8% increase over 2010, growing at a compound rate of 6.9% annually. The distribution of thermal energy used by category is approximately 55.2% for ground-source heat pumps, 20.2% for bathing and swimming (including balneology), 15.0% for space heating (of which 89% is for district heating), 4.9% for greenhouses and open ground heating, 2.0% for aquaculture pond and raceway heating, 1.8% for industrial process heating, 0.4% for snow melting and cooling, 0.3% for agricultural drying, and 0.2% for other uses. Energy savings amounted to 352 million barrels (52.8 million tonnes) of equivalent oil annually, preventing 46.1 million tonnes of carbon and 149.1 million tonnes of CO2 being released to the atmosphere, this includes savings for geothermal heat pumps in the cooling mode (compared to using fuel oil to generate electricity). Since it was almost impossible to separate direct-use from electric power generation for the following, they are combined:approximately 2218 well were drilled in 42 countries, 34,000 person-years of effort were allocated in 52 countries, and US $20 billion invested in projects by 49 countries.
The efficiency of Geothermal Heat Pumps (GHPs) strongly depends on the site-specific parameters of the ground, which should therefore be mapped for the rational planning of shallow geothermal installations. In this paper, a case study is presented for the potentiality assessment of low enthalpy geothermal energy in the Province of Cuneo, a district of 6900 km2 in Piedmont, NW Italy. The available information on the geology, stratigraphy, hydrogeology, climate etc. were processed and mapped, and conclusions were drawn on the geothermal suitability and productivity of different areas of the territory surveyed.
The mollusk fauna from the Pliocene Viviparus beds of Vukomeričke Gorice hills in central Croatia was investigated at four sites in the region of Kravarsko, S of Zagreb. The region represents a Pleistocene dome-anticline at the southern margin of the Sava depression. Sediments are dominated by clay, bearing some sand, gravel and lignite intercalations. The mollusks, comprising 11 gastropod and 2 bivalve species, prove the studied deposits to derive from the long-lived, highly endemic Lake Slavonia. The taxonomic revisions include the introductions of Viviparus kochanskyae n. sp. for specimens from Lake Slavonia previously identified with V. fuchsi NEUMAYR, 1872 and Prososthenia? praeslavonica n. nom. replacing the primary homonym Hydrobia vitrella BRUSINA, 1897 non Stefanescu, 1896. Recognized as an independent phase in the geodynamic evolution of the Pannonian Basin, the new regional stage Cernikian is introduced for the succession, defined by the complete depositional sequence of the Viviparus beds. Two stratigraphic horizons detected in the studied sites are constrained by the Lower Cernikian Viviparus kochanskyae and the Upper Cernikian Viviparus hoernesi zones and stay in perfect agreement with previous regional data. Timing of the Lake Slavonia history is enabled through several zonal markers calibrated to the Geological Time Scale in the Dacian Basin. Accordingly, the Lower Cernikian transgression dates to c. 4.3 Ma, the Upper Cernikian to c. 3.1 Ma, indicating strong alteration of the lacustrine depositional settings during the Pliocene, most likely related to changes in the regional climate. Interestingly, the second transgression of Lake Slavonia is marked by the evolution of strongly sculptured viviparid shells and coincides with the Pliocene Climate Optimum.
Different methods for the design of Borehole Heat Exchangers are available, as reported for example in the Italian standard UNI 11466. Therefore the question arises about the impact of the design methodology on the final result and its sensitivity to the main design and input parameters.
In this paper two common design approaches, namely the ASHRAE analytical method by Kavanaugh and Rafferty and the GLHEPRO commercial tool, based on g-functions method by Eskilson, are taken into account. The two methods are used to design a BHE field for a GSHP system in two case studies, namely a small-scale residential and a medium-scale commercial building. Moreover, a sensitivity analysis for each method is carried out, considering the influence of the main design choices and uncertainties on the required inputs.
The comparison between the two methods shows that ASHRAE tends to overestimate, up to 27%, the BHE size compared to GLHEPRO. Among the parameters investigated, the heat pump size and the BHE layout modestly affect the final BHE size. In turn, the thermal-vector fluid temperatures on the ground side of the heat pump, the single/double U pipe configuration, the distance among adjacent boreholes and the ground thermal conductivity result in the major influence. In particular it is shown that the uncertainty in the ground thermal conductivity and the choice of the fluid temperatures have a comparable impact on the final sizing as the choice of the sizing method.
Approximately 104 x 106 m3 of oil (39 fields), 6.93 x 106 m3 of condensate (11 fields), and 64.92 x 109 m3 of gas (52 fields), were recovered in the Croatian part of the Pannonian Basin System during 64 years of exploitation (1941– 2005). The production peak was attained between 1980–1989, when exploitation began in 12 new fi elds. Based on their cumulative production, the Croatian oil and gas fi elds can be divided into four groups, and the condensate fields into three groups. Such a division has been supported by analysis of recovery, number of reservoirs, porosity and permeability, age and lithology of reservoir rocks. The longest production period is assumed for the first group of fields ; for oil it is approximately 55 years, for condensate 46 and gas 36 years. In the favourable first group the average number of reservoirs is 16 for oil and 11 for gas. Lithological composition is highly favourable, because reservoirs are represented mostly by sandstones of Pannonian and Pontian age with high porosities and permeabilities. A relatively homogeneous sandstone lithology, including good regional seals like marls, enables an increase in recovery through the use of secondary and tertiary recovery methods. Also, water-flooding will remain the dominant secondary-recovery method for increased production in the future.
The layered thermal conductivity of the bedrock and borehole thermal resistance can be determined with the Distributed Thermal Response Test (DTRT), which is a modification of the conventional Thermal Response Test (TRT). The DTRT enables a more detailed examination of the subsurface thermal properties that are significant in a heterogeneous and anisotropic environment. The objective of this study was to evaluate the DTRT method in its entirety, from measurements to interpretation and the utilization of the results. This report comprises a review of the theory related to the DTRT, a description of the Distributed Temperature Sensing (DTS) method, a case study and comparison of the DTRT method with conventional TRT.
To determine the layered thermal conductivity and borehole thermal resistance, the temperature of the heat carrier fluid was logged with optical fiber cables along the borehole length during different phases of the TRT. Particular interest was paid to borehole recovery after the conventional TRT. The borehole was divided into nine sections, each of 20 meters in length. Then, the infinite line source method combined with the superposition technique (i.e. variable heat rate) was applied to each section, fitting the calculated fluid temperatures to the measured ones and minimizing the error between them. Thus, the layered thermal conductivity and the borehole thermal resistance were assessed.
As a result, the test borehole was considered quite homogeneous, having good thermal conductivity, which nevertheless varied between 2.8–4.2 W/(m·K). The differences in the estimation of the layered thermal conductivity may be attributed to both the measurement technology and interpretation aspects. Because the DTS device was subjected to air temperature variations, the temperature data measured with optical fiber cables was affected by the diurnal air temperature fluctuations. The fact that the temperature strongly affected the heat power leads to the conclusion that the heat power may explain the apparent heterogeneity in thermal conductivity. Moreover, finding the appropriate fitting period and layer sectioning may influence the heterogeneity in thermal conductivity. The borehole geophysical investigations carried out earlier demonstrated
that the bedrock is composed of homogeneous granite and is solid, with no significant changes in rock type being detected. The results from the SEM analysis indicated good thermal conductivity because of the reasonably high quartz content. Variations in the estimation of the borehole thermal resistance can be accumulated from the acquired layered thermal conductivity, which was used as an input parameter when optimizing the layered borehole thermal resistance. Besides, the heterogeneity of the borehole thermal resistance could be due to convective heat transfer in the groundwater, which was not considered in this study, or possibly lateral deviation in the U-pipe along the borehole depth.
The aim of this study was to design a compound transdermal patch containing diclofenac (DA) and teriflunomide (TEF) for the treatment of rheumatoid arthritis (RA).
The various organic amines salts of DA were prepared and their forming was confirmed using DSC and FTIR. The percutaneous permeation of organic amines salt of DA was investigated in vitro using a two-chamber diffusion cell with excised rabbit skin as transdermal barrier. The formulation of the patch was optimized in terms of the concentration of percutaneous permeation enhancer and the loading dose of drugs. The pharmacokinetic behavior of the optimal formulation was studies in rabbits and the anti-inflammatory and analgesic effects of the optimal patch were evaluated with the adjuvant arthritis model in rats and the pain model in mice, respectively.
The result showed that skin penetration of diclofenac-triethylamine (DA-TEtA) salt was better than other organic amine salts. Based on previous study of our laboratory, teriflunomide-triethylamine (TEF-TEtA) significantly enhanced the skin permeation of TEF. 10% of azone (AZ) was the best enhancer for the two drugs. The optimal patch formulation was composed of 2% of TEF-TEtA, 6% of DA-TEtA and 10% of AZ. The cumulative permeated amount of DA-TEtA in vitro was comparable with that of the commercial diclofenac-diethylamine (DA-DEtA) patch. The absolute bioavailability of TEF-TEtA was 42%, which could achieve the therapeutic drug levels.
In animal study, the optimized compound patch containing DA-TEtA and TEF-TEtA displayed significant anti-inflammatory and analgesic effect, which indicated the potential of the compound patch.
The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two special valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way.
The area of north-western Dinarides and south-western Pannonian basin has been recently explored by two large international seismic experiments. These are active seismic experiment ALP 2002 and recent passive seismic project ALPASS-DIPS (Alpine Lithosphere and Upper Mantle PASsive Seismic Monitoring - DInarides-Pannonian Segment). Our analysis was carried out on profile Alp07, stretching from Istra to the Drava River at Hungarian–Croatian border in a WSW–ENE direction. A rather precise velocity model of the crust and upper mantle has been defined based on tomographic inversion and forward modelling. During the ALPASS-DIPS project temporary seismic stations have been deployed along the Alp07 profile. Teleseismic events recorded at seismic stations were processed using P-receiver function method. Receiver functions have been calculated for all stations along Alp07 profile (Cro_01 to Cro_12) and for station CBP4M located in the northeastern extension of the profile. The arrival times of Ps conversions at Mohorovičić discontinuity are the greatest under the Dinarides (6.6 s). Ps conversion at Moho in the transition zone becomes shallower, with Ps time between 5.5 and 5 s. The minimum Moho Ps time is observed in the Pannonian part, in the range from 3.8 to 4.5 s.
Energy Strategy of the Republic of Croatia by 2020 relies on renewable energy resources as one of the main priorities. The use of geothermal energy sources is specifically encouraged. Within the research project “Research and the Promotion of the Use of Shallow Geothermal Potential in Croatia”, an improved method, the so called distributed thermal response test (DTRT) has been applied on a 100 m deep borehole heat exchanger (double U pipe) within a borehole of 152 mm outer diameter. The fundamental difference from the thermal response test (TRT) is the measurement of the carrier fluid temperature along the borehole heat exchanger (BHE) using an optic fiber cable placed inside the BHE pipes. Hence, in DTRT vertical distribution of the ground thermal conductivity and borehole thermal resistance are determined along the borehole heat exchanger. The undisturbed ground temperature profile along the BHE was also determined using this method. The work presented in this paper shows measurements from the borehole heat exchanger installation located in the city of Osijek, and determination of the ground thermal conductivity for specific geological settings using three different approaches: DTRT, TRT and direct measurement of sediment thermal properties. In a fluvial sedimentary sequence found in Osijek the discrepancy of DTRT and TRT results are 3.65% for thermal conductivity and 2.25% for borehole thermal resistance, while comparison of weighted averaged ground thermal conductivity results of DTRT and the direct thermal measurement yielded difference of 8.74%.
Previous studies in Cyprus classified the island in the category of low enthalpy with high potentials in the usage of geothermal energy for space air-conditioning. Due to the little existing information about the underground thermal properties, an extended geological sampling has been carried out on the island. Measurements of thermal properties have been performed in the laboratory at room temperature for all the collected samples both in their dry and water-saturated state. The impact on thermal conductivity of water in samples, the mineralogical composition, and the geological age of samples have been the objectives of the current study.
When designing ground heat exchangers used with ground source heat pump systems, a critical design property is the thermal conductivity of the ground. Thermal response tests are used to measure the site-specific thermal conductivity and are also used to measure the thermal resistance of a borehole heat exchanger as installed. Thermal response tests are commonly used today for design of multiple borehole ground heat exchangers, where knowledge of the ground thermal properties can help avoid undersizing of ground heat exchangers, leading to poor system performance, and oversizing of ground heat exchangers, leading to overly costly systems. This review covers the development of the mathematical and numerical analysis procedures, development of the hardware and test procedures, and validation of the results. We take a historical perspective, going as far back as Lord Kelvin’s treatment of transient heat conduction problems in the 1880s, further development of which allowed analysis of conductivity measurements from transient needle probes by the 1950s. We focus on development of test rigs and test procedures in the 1980s and 1990s and validation of the measurements. More recent developments are covered throughout the review.
A Project funded by the Research Promotion Foundation of Cyprus was undertaken by the Cyprus University of Technology and other collaborators, to investigate and determine the geothermal parameters of the ground in Cyprus since such information is currently unavailable. The purpose of this paper is to report on the ground temperatures collected by now, at the six representative sites in relation to depth, time of the year, structure of the ground and altitude and report on their impact on the efficiency of Ground Coupled Heat Pumps. Every month since October 2009, the temperature of the ground is being recorded along the depth of the boreholes. It is anticipated that the project will be completed by the end of 2010 and geothermal information will be collected and reported for all six locations. The data collected until now clearly indicate that there is a potential for the efficient use of GCHPs in Cyprus leading to significant savings in power.
A mathematical procedure for optimization of borehole heat exchanger (BHE) fields is presented. If heat extraction and injection is not seasonally balanced, thermal anomalies grow in the ground. These are commonly constrained by regulations and not desirable due to potential decline of the system's performance. We demonstrate, for the case with heat extraction and only partial replenishment, how adjustment of seasonal heating and cooling workloads can mitigate local cooling of the ground. It is revealed that the benefit from mathematical optimization increases with heat extraction/injection imbalance. Evidently, strategic operation of individual BHEs in the field can to some extent compensate for the heat injection deficit. Additionally to the optimization of workloads, we inspect the required number of BHEs for a given heating/cooling demand. The idea is that by sequentially removing least effective BHEs in the field, investment cost are reduced, while the effect on the entire field performance is minimal. We show that such unfavorable BHEs exist mainly in non-optimized fields without replenishment. Thus, our work offer two ways of tuning BHE fields applied for geothermal heating and cooling: workload optimization of individual BHEs and removal of redundant BHEs for a given arrangement.
This paper examines thermal performance of a ground source heat pump (GSHP) system. The GSHP system was installed in an office building in Nuremberg city of Germany. In order to evaluate system performance the GSHP system has been continuously monitored for 4 years. Heating and cooling performance of the GSHP system is analyzed based on the accumulated data.
Major findings of this work include: (1) coefficient of performance (COP) is estimated to be 3.9 for a typical winter day and energy efficiency ratio (EER) is assessed to be 8.0 for a typical summer day. These results indicate that the GSHP system has a higher efficiency for building cooling than building heating. (2) For a long-term period, the seasonal energy efficiency ratio (SEER) of the GSHP system is observed to increase by 8.7% annually, whereas the seasonal COP is decreased by 4.0% over a 4-year period. The heating and cooling performance of the GSHP system migrates in opposite trend is caused by the unevenly distributed heating and cooling load of the building. This phenomenon deserves serious attention in the design of future GSHP systems in order to avoid the reducing of energy efficiency over long-term operation.
Thermal response tests, used to assess the thermal conductivity of the subsurface in the geothermal heating and cooling sector, require a high power source commonly supplied by a fuel generator. Supplying high power for the conventional test, in which with water flows in the ground heat exchanger, is an important source of cost and a new method using a power source of less than 1 kW has been envisioned. Heating cable sections are installed in the standing water column of the exchanger for the proposed test, where recovery temperatures have been positively reproduced with numerical simulations in preparation for field experiments.
Eleven representative sites were selected in this study to present the characteristics of ground thermal properties in Harbin, China. The initial ground temperature field was measured, and the temperature ranges of the solar warming, constant temperature, and increasing temperature layers were determined. The 22 thermal response tests (TRTs) for 11 boreholes were examined with two heating powers (4.2 kW and 6.5 kW). Analysis of thermal properties was performed in the laboratory. A total of 337 representative samples of rock and soil were analyzed, and their thermal properties were measured in laboratory tests, and the results of these tests are not consistent with those of TRTs. The overall characteristics of ground thermal conductivity are determined according to overall distribution.
Sizing of ground-coupled loop heat exchangers (GLHE) depends on the ground thermal conductivity and capacity, and the borehole thermal resistance. One popular method to estimate the thermal parameters is the interpretation of in situ thermal response tests. The modeled response is Tm=(Tin+Tout)/2Tm=(Tin+Tout)/2, the average temperature of the fluid entering and leaving the ground. The TmTm response corresponds to the physically unrealistic hypothesis of constant heat flux along a borehole. Using a 3D finite element model of the borehole, we show that TmTm does not correspond to the fluid mean temperature within the borehole. Accordingly, with TmTm, an overestimation of the borehole thermal resistance results. The resistance overestimation has a noticeable economic impact. We propose instead a new estimator we name “p-linear” average of TinTin and ToutTout with parameter p→-1p→-1, as determined by numerical simulations. We show that the p-linear average closely fits the average fluid temperature computed with the numerical model, hence avoiding bias in estimation of borehole thermal resistance. Finally, we discuss the problem of collinearity arising in the estimation of thermal parameters.
The design of ground source heat pump systems requires values for the ground thermal conductivity and the borehole thermal resistance. In situ thermal response tests (TRT) are often performed on vertical boreholes to determine these parameters. Most TRT analysis methods apply the mean of the inlet and outlet temperatures of the circulating fluid along the entire borehole length. This assumption is convenient but not rigorous. To provide a more general approach, this paper develops an analytical model of the vertical temperature profile in the borehole during the late-time period of the in situ test. The model also includes the vertical temperature profile of the undisturbed ground. The model is verified with distributed temperature measurements along a vertical borehole using fiber optic cables inside a U-tube for the circulating fluid. The borehole thermal resistance is calculated without the need for the mean temperature approximation. In the studied borehole, the mean temperature approximation overestimates the borehole resistance by more than 20%.
The aim of this study is to evaluate the characteristic thermal properties of 208 (thermal response test) TRT data sets collected in Korea. In the evaluation, the line-source model is used in conjunction with the step-wise evaluation to validate the applicability of the model. The applicability of the step-wise evaluation is classified focusing on the convergence criterion of ground thermal conductivities. The ground thermal conductivities were evaluated in the range of 1.73 and 8.56 W/m·K with the mean of 2.55 W/m·K. The corresponding borehole thermal resistances were also obtained in the range between 0.06 and 0.20 m·K/W with the mean 0.13 m·K/W. In order to investigate the availability of the thermal conductivity of the test sites from the geothermal database in Korea, the ground thermal conductivity obtained by TRTs was compared with the mean bedrock thermal conductivity. Comparison of the four major bedrocks in the test sites indicated that the mean differences are 0.34, 0.53, 0.22 and 1.39 W/m·K at the bedrocks of the granite, geneiss, tuff and sandstone areas, respectively.
A conventional thermal response test (TRT) provides a bulk estimate of the subsurface and borehole thermal properties over the length of the ground heat exchanger (GHE). The measurement of temperature inside the borehole during a TRT can be carried out to further determine thermal properties at different depths. The analysis of the transient temperature response is commonly performed with an analytical solution assuming a constant heat injection rate, which does not reproduce the effect of water flow along the pipe of the GHE. This heat transport mechanism can induce a temporal variation of the heat injection rate at depth although heat injection remains constant at the surface. Analysis of synthetic data generated with numerical simulations of TRTs in a layered subsurface was consequently carried out to verify this analytical approach. The program MLU was selected for analyzing the TRTs because of its capacity to take into account multiple layers. Results indicated that the analysis can be improved by accounting for variable heat injection rates determined inside the GHE. Estimation of both the subsurface thermal conductivity and the borehole thermal resistance was within 20% of the expected values, except when the thermal conductivity of the subsurface is low. For a simulation case carried out with a subsurface layer that had a thermal conductivity as low as 1 W m−1 K−1, the borehole thermal resistance could not be determined with significant accuracy.
The effective thermal conductivity of six vertical closed-loop ground heat exchangers (GHEXs), which were installed in a test bed located in Wonju, South Korea, has been experimentally evaluated by performing in-situ thermal response tests (TRTs). To compare the thermal efficiency of the GHEXs in field, various installation conditions are considered such as different grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and shapes of the circulating pipe-section (conventional U-loop type vs. 3-pipe type). From the test results, it can be concluded that the cement grout has higher effective thermal conductivity than the bentonite grout by 7.4–10.1%, and the graphite outperforms the silica sand by 6.7–9.1% as a thermally-enhancing additive. In addition, the new 3-pipe type heat exchange pipe that yields less thermal interference between the inlet and outlet pipes shows better thermal performance over the conventional U-loop type heat exchange pipe by 14.1–14.5%. Based on the results from the in-situ thermal response tests, a series of cost analyses has been carried out to show the applicability of the cement grouting, the graphite additive, and the new 3-pipe type of heat exchange pipe section. For the same condition, the cement grouting can reduce the construction cost of GHEXs by around 40% in the given cost analysis scenario. In addition, an addition of graphite and use the new 3-pipe heat exchange pipe lead to about 8% and 6% cost reduction, respectively.
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
This authoritative guide provides a basis for understanding the emerging technology of ground source heat pumps. It equips engineers, architects, planners, regulators and geologists with the fundamental skills needed to manipulate the ground’s huge capacity to store, supply and receive heat, and to implement technologies (such as heat pumps) to exploit that capacity for space heating and cooling.
The author has geared the book towards understanding ground source heating and cooling from the ground side (the geological aspects), rather than solely the building aspects.
An Introduction to Thermogeology: Ground Source Heating & Cooling explains the science behind thermogeology and offers practical guidance on different design options.
In a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and bore-hole thermal resistance are determined at many instances along the borehole. Here, such a test is carried out at a 260 m deep water filled energy well, equipped with a U-pipe borehole heat exchanger, containing an aqueous solution of ethanol as working fluid. Distributed tempera-ture measurements are carried out using fiber optic cables placed inside the U-pipe, during four test phases: undisturbed ground conditions, fluid pre-circulation, constant heat injection, and borehole recovery. A line source model is used for simulating the borehole thermal re-sponse. Fluid temperature profiles during the test are presented. The results show local varia-tions of the ground thermal conductivity and borehole thermal resistance along the borehole depth, as well as a deviation of the latter as compared to the one resulting from a standard thermal response test.
As part of a new thermal response test (TRT) and to determine ground thermal conductivities, vertical temperature profiles were obtained using retrievable optical fiber sensors inserted into the U-tubes of two ground heat exchangers (GHEs) installed at Maebaru City (Fukuoka, Kyushu) and Kushiro City (Hokkaido), Japan. Measured profiles and outlet temperatures from TRTs were history-matched with the cylindrical source function. Nonlinear regression was used to estimate the vertical distribution of ground thermal conductivities. The computed distribution is consistent with measured data indicating both the reliability of the optical fiber thermometer and TRT interpretation. It is expected that TRTs and optical fiber thermometers will prove to be increasingly useful for optimizing the depth of the GHEs installed in heterogeneous formations, and consequently will minimize installation costs of geothermal heat pump systems.
The design of a ground heat exchanger for Underground Thermal Energy Storage (UTES) applications requires, among other parameters, knowledge of the thermal properties of the soil (thermal conductivity, borehole thermal resistance and undisturbed soil temperature). In situ determination of these properties can be done by installing a vertical borehole heat exchanger (BHE) and performing the so-called thermal response test (TRT). The present paper describes the results of a cooperative work between research groups of Chile and Argentina, which led to the first thermal response test performed in Latin America. A setup for implementing the TRT was prepared at the “Solar Energy Laboratory” of the Technical University Federico Santa Maria, Valparaiso, Chile. The test was realized over 9 days (24 June to 3 July 2003) while inlet and outlet fluid temperatures of the BHE and the ambient temperature were measured every minute. A comparison between conventional slope determination method, Geothermal Properties Measurement (GPM) data evaluation software based on numerical solutions to the differential equations governing the heat transfer processes and two variable-parameter fitting was performed in order to calculate the thermal conductivity and borehole thermal resistance. The detailed study of ground properties in different regions of Chile and Latin America (Argentina, Brazil) is a good precondition for future investigation and application of the Borehole Thermal Energy Storage (BTES) technology in the region.
Mesozoic to Cenozoic evolution of the central part of the Adriatic plate (External Dinarides and Adriatic foreland) is still a matter of debate. This is expressed by opposing paleogeographic models: single carbonate platform (Adriatic or Adriatic–Dinaridic) versus two carbonate platforms (Adriatic and Dinaridic) separated by the inter-platform Budva–Cukali basin. Estimates of shortening during Adria NE subduction, that resulted in the development of the Dinaric Alps, differ substantially. The single-platform model involves minor shortening achieved by folding and faulting along steep reverse faults. The two-platform model involves significant shortening achieved mainly by thrust stacking, which resulted in almost complete underthrusting of the intervening basinal deposits.
In recent years, several larger geothermal heat pump plants for offices or commercial areas have been designed and built in the central region of Germany, mainly in the Rhein-Main area. Systems with borehole heat exchangers (BHE; in the USA the term Vertical Loop is commonly used) as well as with shallow geothermal doublets (groundwater wells) are operational. New solutions had to be found to adapt the technology to certain site constraints, and innovative components such as thermally-enhanced grouting material have been used. This paper reviews the early development of Ground Source Heat Pumps (GSHP) for commercial buildings, gives details on a number of recent plants and discusses problems that arose during their realisation: UEG Wetzlar, a building with chemical laboratories and one of the first examples of direct cooling from BHE; DFS Langen (German Air Traffic Control Headquarters), with 154 BHE for heating and cooling, operating without antifreeze; Baseler Platz Frankfurt, a building right in the center of Frankfurt/Main, with a very limited construction site and the problem of avoiding contamination by groundwater pollution found in the neighbourhood; Arcade Hainburg, a small commercial district heated by a heat pump on a doublet more than 200 m deep; other examples and aspects. The experience gained from these plants, and the economic circumstances, will help in the successful realisation of future geothermal heat pump systems in the region.
A large number of ground-coupled heat pump (GCHP) systems have been used in residential and commercial buildings throughout the world due to the attractive advantages of high efficiency and environmental friendliness. This paper gives a detailed literature review of the research and developments of the vertical-borehole GCHP technology for applications in air-conditioning. A general introduction on the ground source heat pump system and its development is briefly presented first. Then, the most typical simulation models of the vertical ground heat exchangers currently available are summarized in detail including the heat transfer processes outside and inside the boreholes. The various design/simulation programs for vertical GCHP systems primarily based on the typical simulation models are also reviewed in this paper. Finally, the various hybrid GCHP systems for cooling or heating-dominated buildings are well described. It is found that the GCHP technology can be used both in cold and hot weather areas and the energy saving potential is significant.
Bacterial analysis from food samples is a highly challenging task because food samples contain intensive interferences from proteins and carbohydrates. Three different conditions of yogurt were analyzed: (1) the fresh yogurt immediately after purchasing, (2) the yogurt after expiry date stored in the refrigerator and (3) the yogurt left outside, without refrigeration. The shelf lives of both these yogurt was compared in terms of the decrease in bacterial signals. AB which initially contained 10(9) cells/mL drastically reduced to 10(7) cells/mL. However, Lin (Feng-Yin) yogurt which initially (fresh) had 10(8) cells/mL, even after two weeks beyond the expiry period showed no marked drop in bacterial count. Conventional MALDI-MS analysis showed limited sensitivity for analysis of yogurt bacteria amidst the complex milk proteins present in yogurt. A cost effective ionic solution, CrO(4)(2-) solution was used to enable the successful detection of bacterial signals (40-fold increased in sensitivity) selectively without the interference of the milk proteins. 0.035 mg of Ag nanoparticles (NPs) were also found to improve the detection of bacteria 2-6 times in yogurt samples. The current approach can be further applied as a rapid, sensitive and effective platform for bacterial analysis from food.
Ground-Source Heat Pump with a 100 m Deep Borehole Heat Exchanger e Start up and First Results, Eurotherm Sustainable Refrigeration and Heat Pump Technology Conference
- V Soldo
- M Rusevljan
- T Curko
- M Grozdek
V. Soldo, M. Rusevljan, T. Curko, M. Grozdek, Ground-Source Heat Pump with
a 100 m Deep Borehole Heat Exchanger e Start up and First Results, Eurotherm Sustainable Refrigeration and Heat Pump Technology Conference,
Stockholm, Sweden, 2010.
Influence of groundwater flow on implementation of distributed thermal response test
- L Boban
- L Lepo Sa
- V Soldo
- M Grozdek
L. Boban, L. Lepo sa, V. Soldo, M. Grozdek, Influence of groundwater flow on
implementation of distributed thermal response test, in: Proceedings of the
24th IIR International Congress of Refrigeration, Yokohama, Japan, 2015.
High performance and highly reliable Raman-based distributed temperature sensors based on correlation-coded OTDR and multimode graded-index fibers
- M A Soto
- P K Sahu
- S Faralli
- G Sacchi
- G Bolognini
- F Di Pasquale
- B Nebendahl
- C Rueck
M.A. Soto, P.K. Sahu, S. Faralli, G. Sacchi, G. Bolognini, F. Di Pasquale,
B. Nebendahl, C. Rueck, High performance and highly reliable Raman-based
distributed temperature sensors based on correlation-coded OTDR and
multimode graded-index fibers, in: Proceedings SPIE 6619, Third European
Workshop on Optical Fibre Sensors, Napoli, Italy, 2007.
Physical Basis of Groundwater Dynamics
- K Urumovi
K. Urumovi c, Physical Basis of Groundwater Dynamics, University of Zagreb,
Zagreb, 2003 (in Croatian).
GeoeneProgramme of Geothermal Energy Utilization, Energy Institute
EIHP, GeoeneProgramme of Geothermal Energy Utilization, Energy Institute
"Hrvoje Po zar", Zagreb, 1998 (in Croatian).
Explanation for the Basic Geological Map of the Republic of Croatia
- I He Cimovi C
I. He cimovi c, Quaternary, in: I. Veli c, I. Vlahovi c (Eds.), Explanation for the
Basic Geological Map of the Republic of Croatia 1:300.000, Croatian Geological
Survey, Zagreb, 2009, pp. 95e101 (in Croatian).
Performance of borehole ground heat exchangers under thermal loads from a school building: full-scale experiment in
- O Mikhaylova
- I W Johnston
- G A Narsilio
- A V Kivi
- R Aditya
- G Noonan
O. Mikhaylova, I.W. Johnston, G.A. Narsilio, A.V. Kivi, R. Aditya, G. Noonan,
Performance of borehole ground heat exchangers under thermal loads from a
school building: full-scale experiment in Melbourne, Australia, in: Proceedings of the World Geothermal Congress, Melbourne, Australia, 2015.
Volari c, I. Penzar, I. Lisac, Climatic Map of Croatia According to K€ oppen Classification for the Period
- B Makjani C
- B Penzar
B. Makjani c, B. Penzar, B. Volari c, I. Penzar, I. Lisac, Climatic Map of Croatia
According to K€ oppen Classification for the Period 1950-1977, Faculty of Science, Zagreb, 1979 (in Croatian).
Thermal Analysis of Heat Extraction Boreholes
- P Eskilson
P. Eskilson, Thermal Analysis of Heat Extraction Boreholes, Doctoral Thesis,
Lund University of Technology, Lund, Sweden, 1987.
Thermal Response Test e Method Development and Evaluation
- S Gehlin
S. Gehlin, Thermal Response Test e Method Development and Evaluation,
Doctoral Thesis, Luleå University of Technology, Sweden, 2002.