1.1 本规程包括使用计算机程序估算包含辐射屏障的阁楼下天花板的热量增益或损失。作为本规程附件的计算机程序提供了一个计算程序，用于估计通过包含桁架或椽安装辐射屏障的阁楼下方天花板的热损失或热增益。该程序也适用于无辐射屏障阁楼下方天花板的热损失或热增益估算。该程序利用逐小时的天气数据来估计逐小时的上限热流。假设天花板下方的房屋内部保持恒定温度。目前，该程序适用于具有无阴影山墙屋顶和水平天花板的矩形楼层平面的斜屋顶阁楼。它不适用于平屋顶、拱形天花板或大教堂天花板的结构。计算精度也受到建筑材料物理性能数据质量的限制，主要是绝缘和辐射屏障，以及天气数据的质量。 1.2 在某些情况下，阁楼中辐射屏障和HVAC管道之间的相互作用可能会对建筑物的热性能产生重大影响。管道包括在附录中给出的计算机模型的扩展中。 1.3 以国际单位制或英寸-磅单位表示的数值应单独视为标准值。每个系统中规定的值可能不是精确的等效值；因此，每个系统应相互独立使用。将两个系统的值合并可能会导致不符合标准。 1.4 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 辐射屏障制造商用总半球发射率来表示其产品的性能。 辐射屏障的目的是减少穿过阁楼空气空间的辐射热传递，从而减少通过阁楼下方天花板的热损失或热增益。热流的减少量将取决于许多因素，例如天气条件、阁楼中的质量或反射绝缘量、屋顶的太阳能吸收率、阁楼和屋顶的几何形状以及阁楼通风的数量和类型。由于这些因素的无限组合，发布每种可能情况的数据是不现实的。 5.2 包含辐射屏障的系统的热损失或热增益的计算在数学上很复杂，由于该方法的迭代性质，最好由计算机处理。 5.3 现在，大多数辐射屏障的生产商和消费者都可以广泛使用计算机，以允许使用这种做法。 5.4 本规程的用户可能希望修改数据输入，以准确表示结构。 也可以修改计算机程序以满足个人需要。此外，可能需要额外的计算，例如，以某种方式对每小时热流进行求和，以获得季节或年度能源使用的估计。这可以使用每小时数据作为整个房屋模型的输入，并通过选择房屋平衡点作为总和中的截止点来实现。

1.1 This practice covers the estimation of heat gain or loss through ceilings under attics containing radiant barriers by use of a computer program. The computer program included as an adjunct to this practice provides a calculational procedure for estimating the heat loss or gain through the ceiling under an attic containing a truss or rafter mounted radiant barrier. The program also is applicable to the estimation of heat loss or gain through ceilings under an attic without a radiant barrier. This procedure utilizes hour-by-hour weather data to estimate the hour-by-hour ceiling heat flows. The interior of the house below the ceiling is assumed to be maintained at a constant temperature. At present, the procedure is applicable to sloped-roof attics with rectangular floor plans having an unshaded gabled roof and a horizontal ceiling. It is not applicable to structures with flat roofs, vaulted ceilings, or cathedral ceilings. The calculational accuracy also is limited by the quality of physical property data for the construction materials, principally the insulation and the radiant barrier, and by the quality of the weather data. 1.2 Under some circumstances, interactions between radiant barriers and HVAC ducts in attics can have a significant effect on the thermal performance of a building. Ducts are included in an extension of the computer model given in the appendix. 1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. 1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Manufacturers of radiant barriers express the performance of their products in terms of the total hemispherical emittance. The purpose of a radiant barrier is to decrease the radiation heat transfer across the attic air space, and hence, to decrease the heat loss or gain through the ceiling below the attic. The amount of decrease in heat flow will depend upon a number of factors, such as weather conditions, amount of mass or reflective insulation in the attic, solar absorptance of the roof, geometry of the attic and roof, and amount and type of attic ventilation. Because of the infinite combinations of these factors, it is not practical to publish data for each possible case. 5.2 The calculation of heat loss or gain of a system containing radiant barriers is mathematically complex, and because of the iterative nature of the method, it is best handled by computers. 5.3 Computers are now widely available to most producers and consumers of radiant barriers to permit the use of this practice. 5.4 The user of this practice may wish to modify the data input to represent accurately the structure. The computer program also may be modified to meet individual needs. Also, additional calculations may be desired, for example, to sum the hourly heat flows in some fashion to obtain estimates of seasonal or annual energy usages. This might be done using the hourly data as inputs to a whole-house model, and by choosing house balance points to use as cutoff points in the summations.