Actively heated fiber optics based thermal response test

2021 ◽  
Author(s):  
Kai Gu ◽  
Bo Zhang ◽  
Bin Shi ◽  
Chun Liu ◽  
Peter Bayer ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Fiber Optics ◽  
Geothermal Energy ◽  
Thermal Response ◽  
Clean Energy ◽  
Accurate Estimation ◽  
Thermal Response Test ◽  
Investigation Method ◽  
Response Test ◽  
Shallow Geothermal Energy

<p>In the pursuit of sustainable development and the mitigation of climate change, shallow geothermal energy has been widely recognized as a type of clean energy with great potential. Accurate estimation of thermal ground properties is needed to optimally apply shallow geothermal energy technologies, which are of growing importance for the heating and cooling sector. A special challenge is posed by the often significant heterogeneity and variability of the geological media at a site.</p><p>As an innovative investigation method, we focus on the actively heated fiber optics-based thermal response test (ATRT) and its application in a borehole in Changzhou, China. A copper mesh heated optical cable (CMHC), which both serves as a heating source and a temperature sensing cable, was applied in the borehole. By inducing the electric current to the cable at a relatively low power of 26 W/m, the in-situ heating process was recorded at high depth resolution. This information serves to infer the thermal conductivity distribution along the borehole. The presented field experience reveals that the temperature rise in the early phase of the test should not be used due to initial heat accumulation caused by the outer jacket of the CMHC. The comparison of these results with those of a conventional thermal response test (TRT) and a distributed thermal response test (DTRT) in the same borehole confirmed that the ATRT result is reliable (with a difference less than 5% and 1%, respectively). Most importantly, this novel method affords much less energy and testing time.</p><p>Additionally, to estimate the uncertainty and limits associated with the method, a 2D axisymmetric numerical model based on COMSOL Multiphysics® has been developed. The results indicate that an accurate calculated thermal conductivity requires heating duration to be in the range of 90~400 min considering test efficiency and cost. Our study promotes ATRT as an advanced geothermal field investigation method and it also extends the applicability of the thermal response test as a downhole tool for measurement of soil hydraulic properties.</p>

An Investigation of Hydrological Effects on the Thermal Performance of Standing Column Well Using the in-situ Thermal Response Test

2019 ◽  
Vol 27 (02) ◽  
pp. 1950015 ◽  
Author(s):  
Keun Sun Chang ◽  
Young Jae Kim ◽  
Min Jun Kim
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Flow Rate ◽  
Large Scale ◽  
Thermal Response ◽  
Thermal Response Test ◽  
Response Test ◽  
Geological Conditions ◽  
Wide Range ◽  
Borehole Thermal Resistance

The standing column well (SCW) for ground source heat pump (GSHP) systems is a highly promising technology with its high heat capacity and efficiency. In this study, a large-scale thermal response tester has been built, which is capable of imposing a wide range of heat on the SCW ground heat exchangers and measuring time responses of their thermal parameters. Two standing column wells in one site but with different well hydrological and geological conditions are tested to study their effects on the thermal performances. Borehole thermal resistance ([Formula: see text]) and the effective thermal conductivity ([Formula: see text]) are derived from data obtained from the thermal response test (TRT) by using a line source method. Results show that the influence of groundwater movement on the thermal conductivity of the SCW is not very significant (3.6% difference between two different geological conditions). This indicates that results of one TRT measurement can be applied to other SCWs in the same site, with which considerable time and cost are saved. The increase of circulation flow rate enhances the ground thermal conductivity moderately (4.5% increase with flow rate increase of 45%), but the borehole thermal resistance is substantially lowered (about 25.9%).

scholarly journals Analysis of Relaxation Time of Temperature in Thermal Response Test for Design of Borehole Size

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3297
Author(s):  
Hobyung Chae ◽  
Katsunori Nagano ◽  
Yoshitaka Sakata ◽  
Takao Katsura ◽  
Ahmed A. Serageldin ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Heat Exchange ◽  
Exchange Rates ◽  
Effective Thermal Conductivity ◽  
Thermal Response ◽  
Thermal Response Test ◽  
Vertical Temperature Profile ◽  
Response Test

A new practical method for thermal response test (TRT) is proposed herein to estimate the groundwater velocity and effective thermal conductivity of geological zones. The relaxation time of temperature (RTT) is applied to determine the depths of the zones. The RTT is the moment when the temperature in the borehole recovers to a certain level compared with that when the heating is stopped. The heat exchange rates of the zones are calculated from the vertical temperature profile measured by the optical-fiber distributed temperature sensors located in the supply and return sides of a U-tube. Finally, the temperature increments at the end time of the TRT are calculated according to the groundwater velocities and the effective thermal conductivity using the moving line source theory applied to the calculated heat exchange rates. These results are compared with the average temperature increment data measured from each zone, and the best-fitting value yields the groundwater velocities for each zone. Results show that the groundwater velocities for each zone are 2750, 58, and 0 m/y, whereas the effective thermal conductivities are 2.4, 2.4, and 2.1 W/(m∙K), respectively. The proposed methodology is evaluated by comparing it with the realistic long-term operation data of a ground source heat pump (GSHP) system in Kazuno City, Japan. The temperature error between the calculated results and measured data is 6.4% for two years. Therefore, the proposed methodology is effective for estimating the long-term performance analysis of GSHP systems.

Comparison between traditional and enhanced Thermal Response Test for ground thermal properties estimation

2021 ◽  
Author(s):  
Antonio Galgaro ◽  
Alberto Carrera ◽  
Eloisa Di Sipio
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Heat Exchangers ◽  
Thermal Response ◽  
Physical Parameters ◽  
Thermal Response Test ◽  
Wireless Data ◽  
Stratigraphic Sequence ◽  
Response Test ◽  
Geological Unit

<p>For the design and implementation of an efficient Ground Source Heat Pump (GSHP) system, the local<br>subsoil represents the core element. Since the thermal performance of Borehole Heat Exchangers (BHEs) is<br>site-specific, its planning typically requires the knowledge of the thermal proprieties of the ground, which<br>are influenced by the local stratigraphic sequence and the hydrogeological conditions. The evaluation of<br>the variations of the ground thermal conductivity (TC) along the depth, as well as its undisturbed<br>temperature, are essential to correctly plan the BHEs field and improve the performance of the ground<br>heat exchangers themselves.<br>Thermal Response Test (TRT) is a well-known experimental procedure that allows to obtain the thermal<br>properties of the ground. However, the traditional method provides a single value of the equivalent TC and<br>the undisturbed temperature, which can be associated with the average value over the entire BHE length,<br>with no chance to detect the thermo-physical parameters variations with depth and to discriminate the<br>contributions of the different geological levels crossed by the geothermal exchange probe. Indeed,<br>different layers within a stratigraphic sequence, may have different thermal properties, according to the<br>presence and to the flow rate of groundwater, as well as to granulometry and mineralogical composition,<br>density, and porosity of the lithologies. The identification of the different contributions to the thermal<br>exchange provided by each geological unit, in practice, can further support BHE design, helping to<br>determine the most suitable borehole length and number, achieving the highest heat exchange capability<br>at the lower initial cost of implementing of the entire geothermal plant.<br>In the last years, new improved approaches to execute an enhanced thermal response test have been<br>developed, as the pioneer wireless data transmission GEOsniff technology (enOware GmbH) tested in this<br>study. This measurement method is characterized by its sensors, 20mm-diameter marbles equipped by<br>pressure and temperature transducers combined with a system of data storing and wireless data<br>transmission. Released at regular intervals down the testing BHE, infilled with water, each marble freely<br>floats allowing the measurement of the water temperature variations over time at different depths, in<br>order to identify areas with particular values of thermal conductivity related to distinctive hydrogeological<br>conditions or lithological assessment. This way, the GEOsniff technology allows a high-resolution spatially-<br>distributed representation of the subsoil thermal properties along the BHE.<br>In this work, we present the test outputs acquired at the new humanistic campus of the University of<br>Padova, located in the Eastern Po river plain (Northern Italy). The thermal conductivity data obtained by<br>the GEOsniff method have been compared and discussed, by considering the standard TRT outputs. This<br>innovative technique looks promising to support the optimization of the borehole length in the design<br>phase, even more where the complexity of the treated geological setting increases.</p>

scholarly journals Prediction of Layered Thermal Conductivity Using Artificial Neural Network in Order to Have Better Design of Ground Source Heat Pump System

Energies ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1896 ◽  
Author(s):  
Yanjun Zhang ◽  
Ling Zhou ◽  
Zhongjun Hu ◽  
Ziwang Yu ◽  
Shuren Hao ◽  
...  
Keyword(s):  
Neural Network ◽  
Thermal Conductivity ◽  
Artificial Neural Network ◽  
Thermal Response ◽  
Thermal Response Test ◽  
Study Region ◽  
Response Test ◽  
Ground Source ◽  
Ann Models ◽  
Artificial Neural

Ground source heat pumps (GSHPs) have been widely applied worldwide in recent years because of their high efficiency and environmental friendliness. An accurate estimation of the thermal conductivity of rock and soil layers is important in the design of GSHP systems. The distributed thermal response test (DTRT) method incorporates the standard test with a pair of fiber optic-distributed temperature sensors in the U-tube to accurately calculate the layered thermal conductivity of the rock/soil. In this work, in situ layered thermal conductivity was initially obtained by DTRT for four boreholes in the study region. A series of laboratory tests was also conducted on the rock samples obtained from drilling. Then, an artificial neural network (ANN) model was developed to predict the layered thermal conductivity on the basis of the DTRT results. The primary modeling factors were water content, density, and porosity. The results showed that the ANN models can predict the layered thermal conductivity with an absolute error of less than 0.1 W/(m·K). Finally, the trained ANN models were used to predict the layered thermal conductivity for another study region, in which only the effective thermal conductivity was measured with the thermal response test (TRT). To verify the accuracy of the prediction, the product of pipe depth and layered thermal conductivity was suggested to represent heat transfer capacity. The results showed that the discrepancies between the TRT and ANN models were 5.43% and 6.37% for two boreholes, respectively. The results prove that the proposed method can be used to determine layered thermal conductivity.

scholarly journals Experimental determination of thermal conductivity of soil with a thermal response test

2012 ◽  
Vol 16 (4) ◽  
pp. 1117-1126 ◽  
Author(s):  
Milos Banjac ◽  
Maja Todorovic ◽  
Milan Ristanovic ◽  
Radoslav Galic
Keyword(s):  
Thermal Conductivity ◽  
Experimental Determination ◽  
Outer Part ◽  
Thermal Response ◽  
Heating System ◽  
Thermal Response Test ◽  
Response Test ◽  
In Situ Conditions

Optimal design of a borehole heat exchanger, as the outer part of a ground source heat pump heating system, requires information on the thermal properties of the soil. Those data, the effective thermal conductivity of the soil ?eff and the average temperature of the soil T0, enable us to determine the necessary number and depth of boreholes. The determination of thermal conductivity of the soil in laboratory experiments does not usually coincide with the data under in-situ conditions. Therefore, an in-situ method of experimental determination of these parameters, the so-called thermal response test, is presented in this paper. In addition to the description of the experimental procedure and installation overview, the paper describes methods based on theory and presents their basic limitations, through the presentation of experimental data.

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