scholarly journals Distributed Thermal Response Tests Using a Heating Cable and Fiber Optic Temperature Sensing

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3059 ◽  
Author(s):  
Maria Vélez Márquez ◽  
Jasmin Raymond ◽  
Daniela Blessent ◽  
Mikael Philippe ◽  
Nataline Simon ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Fiber Optic ◽  
Thermal Response ◽  
Power Source ◽  
Temperature Sensing ◽  
Continuous Heating ◽  
Heating Cable ◽  
Conventional Test ◽  
Heat Injection

Thermal response tests are used to assess the subsurface thermal conductivity to design ground-coupled heat pump systems. Conventional tests are cumbersome and require a source of high power to heat water circulating in a pilot ground heat exchanger. An alternative test method using heating cable was verified in the field as an option to conduct this heat injection experiment with a low power source and a compact equipment. Two thermal response tests using heating cable sections and a continuous heating cable were performed in two experimental heat exchangers on different sites in Canada and France. The temperature evolution during the tests was monitored using submersible sensors and fiber optic distributed temperature sensing. Free convection that can occur in the pipe of the heat exchanger was evaluated using the Rayleigh number stability criterion. The finite and infinite line source equations were used to reproduce temperature variations along the heating cable sections and continuous heating cable, respectively. The thermal conductivity profile of each site was inferred and the uncertainly of the test was evaluated. A mean thermal conductivity 15% higher than that revealed with the conventional test was estimated with heating cable sections. The thermal conductivity evaluated using the continuous heating cable corresponds to the value estimated during the conventional test. The average uncertainly associated with the heating cable section test was 15.18%, while an uncertainty of 2.14% was estimated for the test with the continuous heating cable. According to the Rayleigh number stability criterion, significant free convection can occur during the heat injection period when heating cable sections are used. The continuous heating cable with a low power source is a promising method to perform thermal response tests and further tests could be carried out in deep boreholes to verify its applicability.

An Experimental Study on the Thermal Performance Evaluation of SCW Ground Heat Exchanger

2017 ◽  
Vol 25 (01) ◽  
pp. 1750006 ◽  
Author(s):  
Keun Sun Chang ◽  
Min Jun Kim ◽  
Young Jae Kim
Keyword(s):  
Thermal Conductivity ◽  
Performance Evaluation ◽  
Heat Exchanger ◽  
Effective Thermal Conductivity ◽  
Thermal Performance ◽  
Thermal Response ◽  
High Heat ◽  
Injection Rate ◽  
Operating Parameters ◽  
Ground Heat Exchanger

In recent years, application of the standing column well (SCW) ground heat exchanger (GHX) has been noticeably increased as a heat transfer mechanism of ground source heat pump (GSHP) systems with its high heat capacity and efficiency. Determination of the ground thermal properties is an important task for sizing and estimating cost of the GHX. In this study, an in situ thermal response test (TRT) is applied to the thermal performance evaluation of SCW. Two SCWs with different design configurations are installed in sequence to evaluate their effects on the thermal performance of SCW using a single borehole. A line source method is used to derive the effective thermal conductivity and borehole thermal resistance. Effects of operating parameters are also investigated including bleed, heat injection rate, flow rate and filler height. Results show that the effective thermal conductivity of top drawn SCW (Type A) is 11.7% higher than that of bottom drawn SCW (Type B) and of operating parameters tested bleed is the most significant one for the improvement of the thermal performance (40.4% enhanced in thermal conductivity with 10.9% bleed).

scholarly journals Method of Averaging the Effective Thermal Conductivity Based on Thermal Response Tests of Borehole Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3737
Author(s):  
Aneta Sapińska-Śliwa ◽  
Tomasz Sliwa ◽  
Kazimierz Twardowski ◽  
Krzysztof Szymski ◽  
Andrzej Gonet ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Effective Thermal Conductivity ◽  
Heat Exchangers ◽  
Thermal Response ◽  
Method Of Averaging ◽  
Thermal Response Test ◽  
Borehole Heat Exchanger ◽  
Measurement Results ◽  
Borehole Heat Exchangers

This work concerns borehole heat exchangers and their testing using apparatus for thermal response tests. In the theoretical part of the article, an equation was derived from the known equation of heat flow, on which the interpretation of the thermal response test was based. The practical part presents the results of several measurements taken in the AGH Laboratory of Geoenergetics. They were aimed at examining the potential heat exchange capacity between the heat carrier and rock mass. Measurement results in the form of graphs are shown in relation to the examined, briefly described wells. Result analysis made it possible to draw conclusions regarding the interpretation of the thermal response test. The method of averaging the measurement results was subjected to further study. The measuring apparatus recorded data at a frequency of one second, however such accuracy was too large to be analyzed efficiently. Therefore, an average of every 1 min, every 10 min, and every 60 min was proposed. The conclusions stemming from the differences in the values of effective thermal conductivity in the borehole heat exchanger, resulting from different data averaging, were described. In the case of three borehole heat exchangers, ground properties were identical. The effective thermal conductivity λeff was shown to depend on various borehole heat exchanger (BHE) designs, heat carrier flow geometry, and grout parameters. It is important to consider the position of the pipes relative to each other. As shown in the charts, the best (the highest) effective thermal conductivity λeff occurred in BHE-1 with a coaxial construction. At the same time, this value was closest to the theoretical value of thermal conductivity of rocks λ, determined on the basis of literature. The standard deviation and the coefficient of variation confirmed that the effective thermal conductivity λeff, calculated for different time intervals, showed little variation in value. The values of effective thermal conductivity λeff for each time interval for the same borehole exchanger were similar in value. The lowest values of effective thermal conductivity λeff most often appeared for analysis with averaging every 60 min, and the highest—for analysis with averaging every 1 min. For safety reasons, when designing (number of BHEs), safer values should be taken for analysis, i.e., lower, averaging every 60 min.

scholarly journals Thermal performance of the ground in geothermal pavements

2020 ◽  
Vol 205 ◽  
pp. 06015
Author(s):  
Yaser Motamedi ◽  
Nikolas Makasis ◽  
Arul Arulrajah ◽  
Suksun Horpibulsuk ◽  
Guillermo Narsilio
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Thermal Response ◽  
Geothermal Heat ◽  
Capital Costs ◽  
Ground Source ◽  
Shallow Geothermal Energy ◽  
Novel Concept ◽  
Response Testing ◽  
The Impact

Shallow geothermal energy utilises the ground at relatively shallow depths as a heat source or sink to efficiently heat and cool buildings. Geothermal pavement systems represent a novel concept where horizontal ground source heat pump systems (GSHP) are implemented in pavements instead of purpose-built trenches, thus reducing their capital costs. This paper presents a geothermal pavement system segment (20m × 10m) constructed and monitored in the city of Adelaide, Australia, as well as thermal response testing (TRT) results. Pipes have been installed in the pavement at 0.5 m depth, and several thermistors have been placed on the pipes and in the ground. A TRT has been performed with 6kW heating load to achieve an understanding of the thermal response of the system as well as to estimate the effective thermal conductivity of the ground. The results show that the conventional semi-log method may be applicable to determine the thermal conductivity for geothermal pavements. The geothermal heat exchanger at shallow depth is considerably under the influence of the ambient temperature; however, it is still acceptable for exchanging the heat within the ground. It is also concluded that the impact radius of heat exchanger in geothermal pavement during the TRT is around 0.5m in the vertical and horizontal directions for this case study.

Use of a fiber optic distributed temperature sensing system for thermal response testing of ground-coupled heat exchangers

Geothermics ◽  
2018 ◽  
Vol 71 ◽  
pp. 331-338 ◽  
Author(s):  
Christian Herrera ◽  
Gregory Nellis ◽  
Douglas Reindl ◽  
Sanford Klein ◽  
James M. Tinjum ◽  
...  
Keyword(s):  
Heat Exchangers ◽  
Fiber Optic ◽  
Thermal Response ◽  
Temperature Sensing ◽  
Distributed Temperature Sensing ◽  
Sensing System ◽  
Response Testing

scholarly journals Analysis on Thermal Performance of Ground Heat Exchanger According to Design Type Based on Thermal Response Test

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 651 ◽  
Author(s):  
Sang Bae ◽  
Yujin Nam ◽  
Jong Choi ◽  
Kwang Lee ◽  
Jae Choi
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Thermal Resistance ◽  
Heat Pump ◽  
Thermal Performance ◽  
Thermal Response ◽  
Ground Heat Exchanger ◽  
Thermal Response Test ◽  
Borehole Thermal Resistance

A ground source heat pump (GSHP) system has higher performance than air source heat pump system due to the use of more efficient ground heat source. However, the GSHP system performance depends on ground thermal properties and groundwater conditions. There are many studies on the improvement of GSHP system by developing ground heat exchanger (GHX) and heat exchange method. Several studies have suggested methods to improve heat exchange rate for the development of GHX. However, few real-scale experimental studies have quantitatively analyzed their performance using the same ground conditions. Therefore, the objective of this study was to evaluate the thermal performance of various pipe types of GHX by the thermal response test (TRT) under the same field and test conditions. Four kinds of GHX (HDPE type, HDPE-nano type, spiral fin type, and coaxial type) were constructed in the same site. Inlet and outlet temperatures of GHXs and effective thermal conductivity were measured through the TRT. In addition, the borehole thermal resistance was calculated to comparatively analyze the correlation of the heat exchange performance with each GHX. Result of the TRT revealed that averages effective thermal conductivities of HDPE type, HDPE-nano, spiral fin type, and coaxial type GHX were 2.25 W/m·K, 2.34 W/m·K, 2.55 W/m·K, and 2.16 W/m·K, respectively. In the result, it was found that the average borehole thermal resistance can be an important factor in TRT, but the effect of increased thermal conductivity of pipe material itself was not significant.

scholarly journals Modeling the time evolution of geothermal boreholes during peak heating and cooling demands

2021 ◽  
Vol 2116 (1) ◽  
pp. 012101
Author(s):  
Juan Manuel Rivero ◽  
Miguel Hermanns
Keyword(s):  
Heat Exchanger ◽  
Theoretical Model ◽  
Thermal Inertia ◽  
Thermal Response ◽  
Extreme Temperatures ◽  
Geothermal Heat ◽  
Pipe Length ◽  
Heating And Cooling ◽  
Geothermal Heat Exchanger ◽  
Heat Injection

Abstract A geothermal heat exchanger requires special care in its design when it comes to peak heating and cooling demands of the building as the installation may incur in material damages due to the extreme temperatures reached by the heat carrying liquid. The peak demands tend to last a few days at most and the theoretical model used to predict the thermal response of the geothermal heat exchanger has, therefore, to consider the thermal inertia of the heat carrying liquid, the grout, and the ground close to the boreholes. With this in mind, the present work discusses a theoretical model that provides, among other things, the heat injection rates per unit pipe length of the different pipes in the borehole in terms of the bulk temperatures of the heat carrying liquid during those peak heating and cooling demands.

Leakage detection of water pipelines based on active thermometry and FBG based quasi-distributed fiber optic temperature sensing

2021 ◽  
pp. 1045389X2098700
Author(s):  
Weijie Li ◽  
Tiejun Liu ◽  
Huangbin Xiang
Keyword(s):  
Fiber Optic ◽  
Temperature Response ◽  
Economic Loss ◽  
Temperature Sensing ◽  
Leakage Detection ◽  
Water Transportation ◽  
Heating Cable ◽  
Water Pipelines ◽  
Thermal Sensing ◽  
Fiber Optic Temperature

Water pipelines are the efficient and reliable way for water transportation. Leakage of pipelines can lead to tremendous waste of water resources and large economic loss. In this paper, a novel leakage detection method was proposed based on active thermometry and fiber Bragg grating (FBG) based quasi-distributed fiber optic temperature sensing. In this method, the thermal sensing cable was fabricated by coupling heating cable with quasi-distributed temperature sensors. The heat was introduced by the heating cable and the temperature response was measured by the quasi-distributed fiber optic temperature sensor concurrently. The leakage can be detected and located by identifying the local low values in the temperature profile along the pipelines. The feasibility of the proposed method was validated by finite element simulation and experimental investigation. Good agreement between simulation and experimental study was achieved. The results confirmed the effectiveness of the proposed method for leakage detection.

Determination of thermal conductivities in the laboratory and the field: A comparison

2020 ◽  
Author(s):  
Linda Schindler ◽  
Sascha Wilke ◽  
Simon Schüppler ◽  
Christina Fliegauf ◽  
Hanne Karrer ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Thermal Response ◽  
Field Measurements ◽  
Mineralogical Composition ◽  
Fundamental Parameter ◽  
Test Field ◽  
Borehole Heat Exchanger ◽  
Drilling Core ◽  
Thermal Conductivities

<p>The thermal conductivity of the subsurface is a fundamental parameter for the design of borehole heat exchangers in shallow geothermal energy systems. An average thermal conductivity value is usually assumed. Under real conditions, however, the thermal conductivity at depth can vary considerably depending on the local petrophysical and mineralogical properties of the subsurface (e.g. porosity). Hence, the aim of this study was to compare these properties of the subsurface with the thermal conductivities measured in the laboratory and in the field and to highlight possible correlations. For this purpose, a test field was established in the northern Black Forest (Germany) by obtaining an undisturbed drilling core of about 100 m length from sandstone of the Middle to Upper Buntsandstein formation and then installing a borehole heat exchanger (BHE). Various rock parameters were determined in the laboratory on 160 selected samples of the drilling core. Among other parameters, thermal conductivities under saturated and unsaturated conditions were measured and compared with values determined by depth-resolved classical and enhanced thermal response tests in the borehole heat exchanger (TRT). Furthermore, the porosity, permeability, grain density and pore diameter as well as mineralogical composition of the sandstone were intensively studied in the laboratory. The results do not show clear correlations between thermal conductivity, permeability and density. In contrast to those reported in literature, our results indicate a moderate correlation between porosity and thermal conductivity and a more pronounced dependence on grain size.</p><p>With regard to the depth profile of the thermal conductivity, the results between laboratory and field measurements were mainly consistent. The highest thermal conductivities (4.3 W/mK in the laboratory and 4.5 W/mK in the field) confirm the suitability of the Upper and Middle Buntsandstein formation for shallow geothermal installations. Most of these rocks represent typical fluvial deposits, so that the results obtained can be easily transferred to other regions with similar sandstone deposits.</p>

scholarly journals Colloquium 2016: Assessment of subsurface thermal conductivity for geothermal applications

2018 ◽  
Vol 55 (9) ◽  
pp. 1209-1229 ◽  
Author(s):  
Jasmin Raymond
Keyword(s):  
Thermal Conductivity ◽  
Earth Science ◽  
Cooling System ◽  
Thermal Response ◽  
Heat Pumps ◽  
Geothermal System ◽  
Heating And Cooling ◽  
Heating Cable ◽  
Geophysical Well Logs ◽  
Transient Thermal

The construction of “green” buildings using geothermal energy requires knowledge of the ground thermal conductivity, assessed when designing the heating and cooling system of commercial buildings with ground-coupled heat pumps. The most commonly used method for active field assessment is the thermal response test (TRT), which consists of circulating heated water in a pilot ground heat exchanger (GHE) where temperature and flow rate are monitored. The transient thermal perturbation is analyzed to evaluate the subsurface thermal conductivity. Heat injection can also be performed with a heating cable in the GHE to conduct a TRT without water circulation, which can be affected by surface temperature variations. Passive methods, such as the interpretation of geophysical well logs and the analysis of temperature profiles measured in exploration wells, are emerging as alternatives to TRTs. Steady-state and transient laboratory measurements performed on samples collected in surface outcrops or drill cores can also be achieved. Methods to characterize the subsurface in the context of geothermal system design have evolved significantly since the original TRT concept proposed during the 1980s with different techniques inspired from the Earth science sector.

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