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.

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 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.

Ground Source Heat Pump Air Conditioning System of Vertical Geothermal Heat Exchangers Heat Transfer Process and Design Calculation Method

2013 ◽  
Vol 291-294 ◽  
pp. 1728-1734
Author(s):  
Shao Qing Liang
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Air Conditioning ◽  
Scientific Basis ◽  
Heat Transfer Process ◽  
Design Calculation ◽  
Geothermal Heat ◽  
Air Conditioning System ◽  
Ground Source ◽  
Geothermal Heat Exchanger

Geothermal heat exchanger is an important part of the GSHP air-conditioning system and different from other traditional air-conditioning systems. This article through to the geothermal heat exchanger heat transfer performance analysis and the design, derived from the geothermal heat exchanger length calculation formula, for actual engineering construction to provide a scientific basis.

Transient Thermal Performance of Rear Door Heat Exchanger in Local Contained Environment During Water Side Failure

2017 ◽  
Author(s):  
Kourosh Nemati ◽  
Husam A. Alissa ◽  
Mohammad I. Tradat ◽  
Bahgat Sammakia
Keyword(s):  
Heat Exchanger ◽  
Thermal Performance ◽  
Data Centers ◽  
Water Flow Rate ◽  
Thermal Response ◽  
Outlet Temperature ◽  
Rear Door ◽  
Liquid Systems ◽  
Transient Thermal ◽  
The Impact

The constant increase in data center computational and processing requirements has led to increases in the IT equipment power demand and cooling challenges of high-density (HD) data centers. As a solution to this, the hybrid and liquid systems are widely used as part of HD data centers thermal management solutions. This study presents an experimental based investigation and analysis of the transient thermal performance of a stand-alone server cabinet. The total heat load of the cabinet is controllable remotely and a rear door heat exchanger is attached with controllable water flow rate. The cooling performances of two different failure scenarios are investigated. One is in the water chiller and another is in the water pump for the Rear Door Heat eXchanger (RDHX). In addition, the study reports the impact of each scenario on the IT equipment thermal response and on the cabinet outlet temperature using a mobile temperature and velocity mesh (MTVM) experimental tool. Furthermore, this study also addresses and characterizes the heat exchanger cooling performance during both scenarios.

scholarly journals Field Test and Numerical Simulation on Heat Transfer Performance of Coaxial Borehole Heat Exchanger

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5471
Author(s):  
Peng Li ◽  
Peng Guan ◽  
Jun Zheng ◽  
Bin Dou ◽  
Hong Tian ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Thermal Response ◽  
Heat Pumps ◽  
Inlet Temperature ◽  
Borehole Heat Exchanger ◽  
Ground Source Heat Pumps ◽  
Ground Source

Ground thermal properties are the design basis of ground source heat pumps (GSHP). However, effective ground thermal properties cannot be obtained through the traditional thermal response test (TRT) method when it is used in the coaxial borehole heat exchanger (CBHE). In this paper, an improved TRT (ITRT) method for CBHE is proposed, and the field ITRT, based on the actual project, is carried out. The high accuracy of the new method is verified by laboratory experiments. Based on the results of the ITRT and laboratory experiment, the 3D numerical model for CBHE is established, in which the flow directions, sensitivity analysis of heat transfer characteristics, and optimization of circulation flow rate are studied, respectively. The results show that CBHE should adopt the anulus-in direction under the cooling condition, and the center-in direction under the heating condition. The influence of inlet temperature and flow rate on heat transfer rate is more significant than that of the backfill grout material, thermal conductivity of the inner pipe, and borehole depth. The circulating flow rate of CBHE between 0.3 m/s and 0.4 m/s can lead to better performance for the system.

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>

Sign in / Sign up

Export Citation Format

Share Document