Many parts of the building envelopes contain enclosed airspaces. Also, the insulating glass units in fenestration systems, such as curtain walls, windows, and skylight devices, contain enclosed spaces that are normally filled with air or heavy gas such as argon, xenon, or krypton. The thermal resistance (R-value) of an enclosed space depends mainly on the type of the filling gas, emissivity of all surfaces that bound the space, the size and orientation of the space, the direction of heat flow through the space, and the respective temperatures of all surfaces that define the space. Assessing the energy performance of building envelopes and fenestration systems, subjected to different climatic conditions, requires accurate determination of the R-values of the enclosed spaces. In this study, a comprehensive review is conducted on the thermal performance of enclosed airspaces for different building applications. This review includes the computational and experimental methods for determining the effective R-value of enclosed reflective airspaces. Also, the different parameters that affect the thermal performance of enclosed airspaces are discussed. These parameters include the following: (a) dimensions, (b) inclination angles, (c) directions of heat flow, (d) emissivity of all surfaces that bound the space, and (e) operating conditions. Moreover, numerical simulations are conducted using a previously developed and validated model to investigate the effect of the inclination angle, direction of heat transfer, and the coating emissivity on the R-values of enclosed spaces when they are filled with different types of gases.

中文翻译：

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不同建筑应用的封闭反射空间的有效 R 值

建筑围护结构的许多部分都包含封闭的空域。此外，开窗系统（例如幕墙、窗户和天窗装置）中的中空玻璃单元包含通常充满空气或重气体（例如氩气、氙气或氪气）的封闭空间。封闭空间的热阻（R 值）主要取决于填充气体的类型、包围空间的所有表面的辐射率、空间的大小和方向、通过空间的热流方向以及定义空间的所有表面的各自温度。评估受不同气候条件影响的建筑围护结构和开窗系统的能源性能，需要准确确定封闭空间的 R 值。在这项研究中，对不同建筑应用的封闭空间的热性能进行了全面审查。本综述包括用于确定封闭反射空域的有效 R 值的计算和实验方法。此外，还讨论了影响封闭空域热性能的不同参数。这些参数包括：(a) 尺寸，(b) 倾角，(c) 热流方向，(d) 限制空间的所有表面的发射率，以及 (e) 操作条件。此外，使用先前开发和验证的模型进行数值模拟，以研究倾斜角、传热方向和涂层发射率对封闭空间充满不同类型气体时 R 值的影响。