Abstract
The present research work reports the experimental investigation of thermal effectiveness of closed loop single and double U-tube borehole heat exchangers (BHEs) of different depths and diameters. All the experiments were carried out by injecting a constant heat to ground for 48 hours using electric heaters of 3 kW and 5 kW capacities. In all the possible cases, constant and transient thermal effectiveness have been investigated to compare the thermal performance of BHEs. It is observed that the transient value of thermal effectiveness is more stable and consistent as compared to constant thermal effectiveness due consideration of borehole temperature variation during the operation in former case. Decreasing borehole depth by 14 % decreases the thermal effectiveness by 15 % in single U-tube BHE and 7 % in double U-tube BHE. Increasing electrical heat injection to the ground shows least influence on the average value of thermal effectiveness of single and double U-tube BHEs.
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Abbreviations
- BHE :
-
Borehole heat exchanger
- H :
-
Depth of borehole (m)
- k eff :
-
Thermal conductivity of ground formation (Wm−1 K−1)
- k b :
-
Thermal conductivity of grouting (Wm−1K−1)
- Q :
-
Heating capacity of the heater (kW)
- r b :
-
Borehole radius (m)
- t :
-
Time (s)
- T :
-
Temperature (°C)
- avg :
-
Average
- b :
-
Borehole
- bt :
-
Borehole, transient
- g :
-
Undisturbed ground
- i :
-
Inlet
- o :
-
Outlet
- α :
-
Thermal diffusivity (m2s−1)
- ε :
-
Thermal effectiveness
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Acknowledgments
The authors would like to acknowledge Architecture & Planning Department of IIT Roorkee, Roorkee, for extending the facilities established from the ZED-i project funded by the Government of India in collaboration with EPSRC-UK and to the Ministry of Human Resources and Development (MHRD), Government of India.
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Satish Kumar is a research scholar at the Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India. He received his M.Tech. degree in Thermal and Fluid Engineering from Indian Institute of Technology BHU (Varanasi) and B.Tech. from Uttar Pradesh Technical University Lucknow in Mechanical Engineering. His research interests include heat transfer, ground source heat pump system, heat exchanger, renewable energy.
K. Murugesan is a Professor at the Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India. He received his Ph.D. from Indian Institute of Technology Madras, Chennai India in 1998. He was a post- doctoral researcher at National Taiwan University, Taiwan (from 2001 to 2005). His research interests include ground source heat pump system, heat and moisture transport through saturated and unsaturated porous media, CFD.
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Kumar, S., Murugesan, K. Effect of operating and geometrical parameters on real-time thermal effectiveness of closed-loop borehole heat exchangers in GSHP application. J Mech Sci Technol 37, 6011–6018 (2023). https://doi.org/10.1007/s12206-023-1037-x
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DOI: https://doi.org/10.1007/s12206-023-1037-x