Numerical simulation and sensitivity study of double-layer Slinky-coil horizontal ground heat exchangers
Numerical simulation and sensitivity study of double-layer Slinky-coil horizontal ground heat exchangers
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DOI：
10.1016/j.geothermics.2013.02.006
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发表时间：
2013-07-01
期刊：
影响因子：
3.9
通讯作者：
Chou, Naokatsu
中科院分区：
文献类型：
--
作者：
Fujii, Hikari;Yamasaki, Shohei;Chou, Naokatsu
在土壤源热泵系统中，由于采用普通的挖掘机就可以建造水平埋管换热器，因此可以大大降低系统的初投资。虽然HGHE在美国和加拿大已被普遍使用，在那里有丰富的土地空间可用于安装HGHE，减少土地面积的要求是很重要的系统更广泛的应用到世界其他地区。为此，如果热交换率远大于单层HGHEs.In这项研究中，长期的冷却和加热测试，使用单层和双层Slinky-coil HGHEs作为热源，在日本福冈进行比较他们的热交换能力，双层Slinky-coil HGHEs的引入被认为是一个有效的选择。试验表明，双层换热器的引入显著提高了单位面积换热器的换热能力。然后，在修改表面边界条件后，根据Fujii等人（2012年）的程序开发了HGHE的数值模拟模型。该模型能够较好地再现制冷和制热试验中热介质（载热流体）的温度特性和地温，验证了双层柔性盘管换热器数值模型的可靠性，并利用该模型进行了灵敏度研究，为双层柔性盘管换热器的优化设计提供了依据。对安装深度的敏感性研究结果表明，在固定下层深度为2.0m的情况下，上层的最佳安装深度为1.5m。对热媒循环的最佳方向进行了研究，得出了由上层向下层循环的结论。最后，通过改变地表反射率为0.1，0.3和0.6，研究了地表反射率的影响。数值模拟结果表明，在加热操作中，较低的热膨胀系数是有利的，而在冷却操作中，较高的热膨胀系数是有利的。(c)2013爱思唯尔有限公司保留所有权利。
In ground-source heat pump (GSHP) systems, the application of Slinky-coil horizontal ground heat exchangers (HGHEs) greatly reduces the initial costs for the system since the HGHEs can be constructed using common excavation machines. Though HGHEs have been commonly used in the United States and Canada, where abundant land space is available for installing HGHEs, the reduction of the land area requirement is important for the wider application of the system to other regions of the world. For this purpose, the introduction of a double-layer Slinky-coil HGHE is considered an effective choice if the heat exchange rates are much more than those for single-layer HGHEs.In this study, long-term cooling and heating tests, using single-layer and double-layer Slinky-coil HGHEs as the heat source, were conducted in Fukuoka, Japan to compare their heat exchange capacities. The tests showed that the heat exchange capacity of HGHEs per unit land area is remarkably enhanced by the introduction of double-layer HGHEs. Numerical simulation models were then developed for the HGHEs on the basis of the procedures of Fujii et al. (2012) after modifications of surface boundary conditions. The models could successfully reproduce the temperature behaviors of the heat medium (heat carrier fluid) and ground temperatures in the cooling and heating tests, demonstrating the reliability of the numerical model for double-layer Slinky-coil HGHEs.Using the model, sensitivity studies were performed to optimize the design of the double-layer HGHEs. The results of the sensitivity study on installation depth showed that the optimum depth of the upper layer was 1.5 m in case that the depth of the lower layer was fixed at 2.0 m. The preferable direction of heat-medium circulation was then investigated and it was concluded that circulation from the upper layer to the lower layer is the most suitable direction. Finally, the influence of the reflectance of the land surface was investigated by changing the albedo of the land surface as 0.1, 0.3 and 0.6. The numerical simulations showed that lower albedo is preferable in heating operations, while higher albedo is favorable in cooling operations. (c) 2013 Elsevier Ltd. All rights reserved.