Evaluation of a Coaxial Borehole Heat Exchanger Prototype

2010 ◽  
Author(s):  
Jose´ Acun˜a ◽  
Palne Mogensen ◽  
Bjo¨rn Palm
Keyword(s):  
Heat Exchanger ◽  
Thermal Response ◽  
Flow Distribution ◽  
Borehole Heat Exchanger ◽  
Tests And Measurements ◽  
Temperature Measurement Point ◽  
Flow Directions ◽  
Central Pipe ◽  
Borehole Thermal Resistance

Different borehole heat exchanger designs have been discussed for many years. However, the U-pipe design has dominated the market, and the introduction of new designs has been practically lacking. The interest for innovation within this field is rapidly increasing and other designs are being introduced on the market. This paper presents a general state of the art summary of the borehole heat exchanger research in the last years. A first study of a prototype coaxial borehole heat exchanger consisting of one central pipe and five external channels is also presented. The particular geometry of the heat exchanger is analyzed thermally in 2-D with a FEM software. An experimental evaluation consisting of two in situ thermal response tests and measurements of the pressure drop at different flow rates is also presented. The latter tests are carried out at two different flow directions with an extra temperature measurement point at the borehole bottom that shows the different heat flow distribution along the heat exchanger for the two flow cases. The borehole thermal resistance of the coaxial design is calculated both based on experimental data and theoretically.

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.

Effect of depth and fluid flow rate on estimate for borehole thermal resistance of single U-pipe borehole heat exchanger

2020 ◽  
Vol 147 ◽  
pp. 2399-2408 ◽  
Author(s):  
Changxing Zhang ◽  
Xinjie Wang ◽  
Pengkun Sun ◽  
Xiangqiang Kong ◽  
Shicai Sun
Keyword(s):  
Fluid Flow ◽  
Heat Exchanger ◽  
Thermal Resistance ◽  
Flow Rate ◽  
Fluid Flow Rate ◽  
Borehole Heat Exchanger ◽  
Borehole Thermal Resistance

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.

Building Performance Simulations coupled to Borehole Heat Exchanger Simulations: a tool for realistic monitoring and forecast

2021 ◽  
Author(s):  
Jan Niederau ◽  
Johanna Fink ◽  
Moritz Lauster
Keyword(s):  
Heat Exchanger ◽  
Thermal Power ◽  
Thermal Response ◽  
Heat Extraction ◽  
Building Performance ◽  
Power Demand ◽  
Outdoor Temperature ◽  
Borehole Heat Exchanger ◽  
Heat Demand ◽  
Demand Models

<p>The actual heat demand of a building depends on various building-specific parameters, such as building age, insulation type, housing volume, but also external parameters, e.g. outdoor temperature. Being able to dynamically model the thermal power demand of a specific building can increase the robustness of coupled borehole heat exchanger simulations (BHE-simulations), as the transient heat demand models of a building / consumer can be used to simulate the thermal response of the subsurface to the prescribed consumer demand.</p><p>We present results of coupling results of Building Performance Simulation (BPS) with simulations of Borehole Heat Exchangers. BPS are carried out using TEASER (Tool for Energy Analysis and Simulation for Efficient Retrofit) which models the thermal power demand of a building based on parameters, such as year of construction, net-lease area, and outdoor-temperature.</p><p>Using annual temperature curves, we model the thermal power demand of buildings from the 1950s, once in original state and in retrofitted state. The thermal response of a connected BHE-field is simulated using SHEMAT-Suite, an open-source simulator for heat- and mass-transfer in porous media. In our BHE simulations, thermal plumes develop as a result of heat-extraction and regional groundwater flow.</p><p>To improve the forecast of, e.g. the magnitude of these plumes, realistic knowledge of the heat demand is important, which can be achieved by the presented coupling of BPS- and BHE-modelling.</p><p><span> </span></p>

scholarly journals In Situ Experiment and Numerical Model Validation of a Borehole Heat Exchanger in Shallow Hard Crystalline Rock

Energies ◽  
2018 ◽  
Vol 11 (4) ◽  
pp. 963 ◽  
Author(s):  
Mateusz Janiszewski ◽  
Enrique Caballero Hernández ◽  
Topias Siren ◽  
Lauri Uotinen ◽  
Ilmo Kukkonen ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Numerical Model ◽  
Model Validation ◽  
Crystalline Rock ◽  
Borehole Heat Exchanger ◽  
In Situ Experiment

Validation of borehole heat exchanger models against multi-flow rate thermal response tests

Geothermics ◽  
2018 ◽  
Vol 71 ◽  
pp. 55-68 ◽  
Author(s):  
Richard A. Beier ◽  
Matt S. Mitchell ◽  
Jeffrey D. Spitler ◽  
Saqib Javed
Keyword(s):  
Heat Exchanger ◽  
Flow Rate ◽  
Thermal Response ◽  
Borehole Heat Exchanger
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