A novel hybrid approach for in-situ determining the thermal properties of subsurface layers around borehole heat exchanger

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.

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Long-term performance evaluation for deep borehole heat exchanger array under different soil thermal properties and system layouts

Energy ◽

10.1016/j.energy.2021.122937 ◽

2021 ◽

pp. 122937

Author(s):

Wanlong Cai ◽

Fenghao Wang ◽

Chaofan Chen ◽

Shuang Chen ◽

Jun Liu ◽

...

Keyword(s):

Performance Evaluation ◽

Thermal Properties ◽

Heat Exchanger ◽

Deep Borehole ◽

Borehole Heat Exchanger ◽

Soil Thermal Properties ◽

Long Term Performance ◽

Term Performance

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

Energies ◽

10.3390/en11040963 ◽

2018 ◽

Vol 11 (4) ◽

pp. 963 ◽

Cited By ~ 4

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

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Evaluation of a Coaxial Borehole Heat Exchanger Prototype

2010 14th International Heat Transfer Conference, Volume 4 ◽

10.1115/ihtc14-22374 ◽

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.

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