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Analysis of the influence of the return position in the vertical temperature gradient in displacement ventilation systems for large halls

机译：大大厅置换通风系统中返回位置对垂直温度梯度的影响分析

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Displacement ventilation systems are widely used in spaces of small and medium heights (up to 7.5 m), taking advantage of their high efficiency in removing contaminants by means of the air stratification. This outcome usually hides major drawbacks compared to admixture systems, such as inadequate temperature gradient in the occupied zone and low cooling capacity. On the contrary, its use in large spaces with high ceilings displays the best features of the system, provided the return is placed near the ceiling. When, due to architectural reasons, this option is not feasible, alternatives for the return position are assessed using simulation tools that result in excessive time consumption during the design stage. In this article a simple Mundt's equation based iterative process is proposed to quickly evaluate the influence of the return height in the vertical temperature gradient and the additional cooling load due to overheated ceiling. It has been applied to the case of Madrid airport new terminal, and their results have been compared to a CFD simulation, with a reasonable degree of accuracy for an initial stage of a design process. The results show that the higher the return is placed, the lesser airflow rate is needed to match the additional cooling load due to radiation from the ceiling. The calculation process also shows that Mundt's radiant heat exchange coefficient is far from being constant, for it is affected by the height of the return point, and takes values much greater than the usually accepted. (C) 2017 Elsevier B.V. All rights reserved.
机译：置换通风系统利用其通过空气分层去除污染物的高效率，广泛用于中小高度（最高7.5 m）的空间。与掺合料系统相比，这种结果通常隐藏着主要的缺点，例如，所占区域的温度梯度不足和冷却能力低。相反，如果将返回装置放置在天花板附近，则该产品在高天花板的大空间中的使用将显示系统的最佳功能。当由于架构原因，此选项不可行时，将使用模拟工具评估返回位置的替代方案，这会导致设计阶段浪费大量时间。在本文中，提出了一个简单的基于Mundt方程的迭代过程，以快速评估返回高度在垂直温度梯度中的影响以及由于天花板过热而产生的额外冷却负荷。它已应用于马德里机场新航站楼，并将其结果与CFD模拟进行了比较，并且在设计过程的初始阶段具有合理的准确性。结果表明，返回的位置越高，由于天花板的辐射而需要的空气流量就越少，以匹配额外的冷却负荷。计算过程还表明，芒特的辐射热交换系数远非恒定，因为它受折返点高度的影响，并且取值远大于通常接受的值。 （C）2017 Elsevier B.V.保留所有权利。

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