| Abstrakt: |
Purpose: A numerical analysis of a single U-tube of borehole heat exchanger (BHE) in a ground source heat pump (GSHP) system containing ground soil and mortar is required to derive expectations for greenhouse cooling and heating. Compared with the 400-m-long ground heat exchanger (GHE), the 200-m-long GHE requires less installation cost and produces stable thermal energy because it only extracts energy where the temperature is stable, making the thermal energy easier to predict. In this study, numerical analysis was performed on a single BHE U-tube at a depth of 200 m in a GSHP system including soil and grout to be used for greenhouse heating and cooling. Methods: A 3D model of the BHE was created using ANSYS Design Modeler 21.1 software. The BHE consists of a single U-tube, working fluid, grout, and surrounding soil. The fluid flow and heat transfer process within a single U-tube GHE follows the laws of mass, momentum, and energy. ANSYS Fluent 21.1 software, a commercial computational fluid dynamics (CFD) program, was used for the numerical analysis. Results: In the cooling condition with the inlet temperature of 308.15 K, the outlet temperatures of 30, 32, 34, and 36 LPM for each volume flow are 301.93, 302.24, 302.52, and 302.77 K, respectively, and the temperature difference is 3.22, 5.91, 50.63, and 5.38 K, respectively. In the heating condition with the inlet temperature of 274.75 K, the outlet temperatures of 30, 32, 34, and 36 LPM for each flow rate are 279.6, 279.35, 279.14, and 278.94 K, respectively, and the temperature difference is 4.85, 4.6, 4.39, and 4.19 K, respectively. The lower the velocity, the higher the inlet and outlet temperature difference. This is because when the flow rate is low, the velocity decreases, and the temperature variation increases. In addition, when the flow rate is high, the velocity increases, and the temperature variation decreases. The heat transfer of 30, 32, 34, and 36 LPM was 12.985, 13.162, 13.319, and 13.468 kW under cooling conditions and 10.109, 10.246, 10.369, and 10.798 kW under heating conditions, respectively. The pressure drops for 30, 32, 34, and 36 LPM are 23.9, 25.872, 27.871, and 31.626 kPa, respectively. As the flow rate increases, the heat transfer increases and the pressure drop also increases. |
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