scholarly journals Comparative Analysis of Different Methodologies Used to Estimate the Ground Thermal Conductivity in Low Enthalpy Geothermal Systems

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1672 ◽  
Author(s):  
Cristina Sáez Blázquez ◽  
Ignacio Martín Nieto ◽  
Arturo Farfán Martín ◽  
Diego González-Aguilera ◽  
Pedro Carrasco García
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Response ◽  
Ground Source Heat Pump ◽  
Thermal Response Test ◽  
Geothermal Systems ◽  
Ground Source ◽  
Accurate Comparison ◽  
The One ◽  
Alternative Solutions

In ground source heat pump systems, the thermal properties of the ground, where the well field is planned to be located, are essential for proper geothermal design. In this regard, estimation of ground thermal conductivity has been carried out by the implementation of different techniques and laboratory tests. In this study, several methods to obtain the thermal properties of the ground are applied in order to compare them with the reference thermal response test (TRT). These methods (included in previous research works) are carried out in the same geological environment and on the same borehole, in order to make an accurate comparison. All of them provide a certain value for the thermal conductivity of the borehole. These results are compared to the one obtained from the TRT carried out in the same borehole. The conclusions of this research allow the validation of alternative solutions based on the use of a thermal conductive equipment and the application of geophysics techniques. Seismic prospecting has been proven as a highly recommendable indicator of the thermal conductivity of a borehole column, obtaining rate errors of below 1.5%.

In-Situ Thermal Response Test for Ground Source Heat Pump Application

2011 ◽  
Author(s):  
Wenzhi Cui ◽  
Quan Liao ◽  
Guiqin Chang ◽  
Qingyuan Peng ◽  
Tien-Chien Jen
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Heat Pump ◽  
Thermal Response ◽  
Ground Source Heat Pump ◽  
Thermal Response Test ◽  
Response Test ◽  
Ground Source ◽  
Borehole Thermal Resistance

The design and performance optimization of ground source heat pump (GSHP) systems need the exact thermal properties of the soil, such as ground thermal conductivity and capacity, and the borehole thermal resistance of borehole heat exchanger (BHE). In-situ thermal response test (TRT) is the most widely used method to determine the overall thermal physical properties of the geological structure around the borehole. A TRT experimental apparatus has been developed and thermal response test was performed in Chongqing, southwest China. Both single-U and double-U borehole heat exchangers are studied in this work. The test duration is about 70 hours. Data direct fitting and parameter estimate method are both used to determine the soil thermal conductivity and the borehole thermal resistance. The results showed that the average ground thermal conductivity of the test region for single U and double U BHE conditions are 2.55 and 2.51 Wm−1K−1, and borehole thermal resistance are 0.116 and 0.066 mKW−1, respectively.

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.

Introduction of a Thermal Response Test (TRT) Apparatus Used for Measuring Underground Heat Exchanger Characteristics

2014 ◽  
Vol 937 ◽  
pp. 381-385
Author(s):  
Yi Liu ◽  
Yang Shi ◽  
Ya Ning Zhang
Keyword(s):  
Heat Exchanger ◽  
Thermal Response ◽  
Heilongjiang Province ◽  
Ground Source Heat Pump ◽  
Thermal Response Test ◽  
Pump System ◽  
Heat Pump System ◽  
Response Test ◽  
Ground Source

Abstract. A thermal response test (TRT) apparatus is introduced in this paper for determination of the performance of underground heat exchanger in ground-source heat pump system. The inlet and outlet temperatures of the underground heat exchanger can be real-time tested to obtain the heat transfer data. The apparatus was used to test a underground heat exchanger for its inlet and outlet temperatures in Red Star farm, Beian City, Heilongjiang province, China. The inlet and outlet temperatures varied in the ranges of 10.62~13.57°C and 9.01~11.88°C within 24 hours, respectively.

scholarly journals Effect of Groundwater Flow and Thermal Conductivity on the Ground Source Heat Pump Performance at Bangkok and Hanoi: A Numerical Study

2021 ◽  
Author(s):  
Arif Widiatmojo ◽  
Youhei Uchida ◽  
Isao Takashima
Keyword(s):  
Thermal Conductivity ◽  
Groundwater Flow ◽  
Heat Pump ◽  
Line Source ◽  
Thermal Response ◽  
Ground Source Heat Pump ◽  
Source Method ◽  
Ground Source ◽  
Apparent Thermal Conductivity ◽  
Infinite Line

In recent decades, the fast-growing economies of Southeast Asian countries have increased the regional energy demand per capita. The statistic indicates Southeast Asian electricity consumption grows for almost 6% annually, with space cooling becoming the fastest-growing share of electricity use. The ground source heat pump technology could be one of the solutions to improve energy efficiency. However, currently, there are limited data on how a ground source heat pump could perform in such a climate. The thermal response test is widely used to evaluate the apparent thermal conductivity of the soil surrounding the ground heat exchanger. In common practice, the apparent thermal conductivity can be calculated from the test result using an analytical solution of the infinite line source method. The main limitation of this method is the negligence of the physical effect of convective heat transfer due to groundwater flow. While convection and dispersion of heat are two distinctive phenomena, failure to account for both effects separately could lead to an error, especially in high groundwater flow. This chapter discusses the numerical evaluation of thermal response test results in Bangkok, Thailand, and Hanoi, Vietnam. We applied a moving infinite line source analytical model to evaluate the value of thermal conductivity and groundwater flow velocity. While determining the ground thermal properties in a high accuracy is difficult, the moving infinite line source method fulfills the limitation of the infinite line source method. Further, we evaluated the five-year performance of the ground source heat pump system coupled with two vertical ground heat exchangers in Bangkok and Hanoi. The results suggest the importance of groundwater flow to enhance the thermal performance of the system.

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