Hasan Nahid, Ali Md Hasan, Pratik Nahyan Ahnaf, Lubaba Nafisa, Miyara Akio
Department of Energy Science and Engineering, Khulna University of Engineering & Technology, Bangladesh.
Department of Mechanical Engineering, Saga University, 1 Honjo-machi, Saga, 840-8502, Japan.
Heliyon. 2024 Aug 2;10(15):e35718. doi: 10.1016/j.heliyon.2024.e35718. eCollection 2024 Aug 15.
Ground heat exchanger (GHE) is the most crucial element of a ground source heat pump (GSHP) system for building cooling and heating by the utilization of geothermal energy. Therefore, intending to enhance the performance of GHE, the present study conducts a computational investigation of the thermal performance of modified spiral tube vertical GHEs. Several modifications of uniform-pitched spiral GHE are made to increase its thermal performance. Some modifications are introduced as variable-pitched spiral tube GHE where spiral inlet pipes are densified in the lower part of GHEs by reducing pitch distance. Conversely, in some modifications, the position of the outlet straight pipe is changed. Water is considered as the working fluid and the inlet temperature of the water is maintained fixed at 300.15 K. After extensive analysis, it is evident that, when the outlet pipe is placed outside of the spiral coil, there is a 7.67 % enhancement in the thermal performance than a traditional uniform-pitched spiral tube GHE. However, modifications like variable-pitched spiral tube GHEs are not significant to improve the thermal performance due to the quick saturation of the ground soil temperature around the GHE pipes. To have a balance between heat transfer rate and pressure drop, thermal performance capability (TPC) and coefficient of performance improvement criterion were evaluated and it is found that the uniform-pitched spiral tube GHE along with the outlet pipe at the outside of the spiral provides maximum thermal performance with a maximum TPC value of 1.062 and provides the positive value of criterion. The positive values of indicate that the spiral tube GHEs are energy efficient based on heat transfer and pressure drop. Moreover, spiral GHE with high-density polyethylene (HDPE), concrete pile, and sandy clay outperform the other materials for pipe, backfill, and soil, respectively. Specifically, HDPE pipe, concrete backfill, and sandy clay as soil offer around 7 %, 5 %, and 7.8 % higher thermal performance compared to polyethylene, sand silica, and clay, respectively.
地源热交换器（GHE）是利用地热能进行建筑供冷和供热的地源热泵（GSHP）系统中最关键的部件。因此，为了提高地源热交换器的性能，本研究对改进型螺旋管垂直地源热交换器的热性能进行了数值研究。对均匀螺距螺旋地源热交换器进行了多种改进以提高其热性能。引入了一些改进措施，如变螺距螺旋管地源热交换器，通过减小螺距距离使螺旋进水管在热交换器下部更密集。相反，在一些改进中，改变了出口直管的位置。水被视为工作流体，水的入口温度保持固定在300.15K。经过广泛分析，很明显，当出口管置于螺旋盘管外部时，与传统的均匀螺距螺旋管地源热交换器相比，热性能提高了7.67%。然而，由于地源热交换器管道周围的地温迅速饱和，变螺距螺旋管地源热交换器等改进措施对提高热性能并不显著。为了在传热速率和压降之间取得平衡，评估了热性能能力（TPC）和性能改进系数标准，发现均匀螺距螺旋管地源热交换器以及出口管位于螺旋外部时具有最大热性能，最大TPC值为1.062，并提供了标准的正值。标准的正值表明螺旋管地源热交换器在传热和压降方面具有能源效率。此外，采用高密度聚乙烯（HDPE）、混凝土桩和砂质粘土的螺旋地源热交换器分别在管材、回填材料和土壤方面优于其他材料。具体而言，与聚乙烯、硅砂和粘土相比，HDPE管、混凝土回填材料和砂质粘土作为土壤分别提供了约7%、5%和7.8%更高的热性能。
