1.1 实践 D7897 适用于模拟现场暴露对屋顶表面材料的太阳反射率和热发射率的影响，包括但不限于现场应用的涂层、工厂应用的涂料、单层膜、改性沥青产品、木瓦、瓷砖和金属产品。屋顶表面材料的太阳反射率和热发射率可以通过暴露在室外环境中而改变。这些变化是由三个因素引起的:空气中污染物的沉积和滞留、微生物的生长以及物理或化学性质的变化。 本规程适用于模拟空气中污染物的沉积和滞留引起的太阳反射率和热发射率的变化，以及在一定程度上模拟微生物生长引起的变化。 1.2 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.3 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ===意义和用途====== 5.1 建筑围护结构表面的太阳反射率影响表面温度和近表面环境空气温度。太阳反射率低的表面吸收大量入射的太阳能。 屋顶或其他建筑围护表面吸收的阳光可以被引导到建筑中，在有空调的建筑中增加冷负荷和减少热负荷，或者在无空调的建筑物中提高室内温度。它还可以通过对流使室外空气变暖。太阳反射率的测定可以帮助设计师和消费者为他们的建筑和社区选择合适的材料。 5.1.1 新建筑围护结构表面的太阳反射率通常在一到两年内因烟尘的沉积和滞留而发生变化； 微生物生长；暴露在阳光、降水和露水中；以及其他污染和风化过程。例如，具有高初始反射率的浅色“冷”包络表面在被深色污染剂覆盖时可能会经历显著的反射率损失。目前的产品评级计划要求屋顶制造商报告三年自然暴露后测得的太阳反射率和热发射率值 ( 2. ， 3. ) 一种快速的实验室土壤和风化过程，模拟了- 屋顶和其他建筑围护结构表面材料的多年辐射特性加速了此类产品的开发、测试和推向市场。 5.2 热发射度描述了表面与其环境交换热辐射的效率。高热发射率增强了表面在阳光下保持凉爽的能力。裸露金属表面的热发射率最初很低，并且通常随着污染或氧化而增加 ( 4. ) .典型的非- 金属表面最初很高，弄脏后仍然很高 ( 5. ) 。 5.3 这种做法允许在应用模拟场暴露后测量屋顶样品的太阳反射率和热发射率。 5.4 本规程旨在被另一个标准（如ANSI/CRRC S100）所引用，该标准规定了试样选择规程和辐射测量方法。

1.1 Practice D7897 applies to simulation of the effects of field exposure on the solar reflectance and thermal emittance of roof surface materials including but not limited to field-applied coatings, factory-applied coatings, single-ply membranes, modified bitumen products, shingles, tiles, and metal products. The solar reflectance and thermal emittance of roof surfacing materials can be changed by exposure to the outdoor environment. These changes are caused by three factors: deposition and retention of airborne pollutants, microbiological growth, and changes in physical or chemical properties. This practice applies to simulation of changes in solar reflectance and thermal emittance induced by deposition and retention of airborne pollutants and, to a limited extent, changes caused by microbiological growth. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.3 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 The solar reflectance of a building envelope surface affects surface temperature and near-surface ambient air temperature. Surfaces with low solar reflectance absorb a high fraction of the incoming solar energy. Sunlight absorbed by a roof or by other building envelope surfaces can be conducted into the building, increasing cooling load and decreasing heating load in a conditioned building, or raising indoor temperature in an unconditioned building. It can also warm the outside air by convection. Determination of solar reflectance can help designers and consumers choose appropriate materials for their buildings and communities. 5.1.1 The solar reflectance of a new building envelope surface often changes within one to two years through deposition and retention of soot and dust; microbiological growth; exposure to sunlight, precipitation, and dew; and other processes of soiling and weathering. For example, light-colored “cool” envelope surfaces with high initial reflectance can experience substantial reflectance loss as they are covered with dark soiling agents. Current product rating programs require roofing manufacturers to report values of solar reflectance and thermal emittance measured after three years of natural exposure ( 2 , 3 ) . A rapid laboratory process for soiling and weathering that simulates the three-year-aged radiative properties of roof and other building envelope surface materials expedites the development, testing, and introduction to market of such products. 5.2 Thermal emittance describes the efficiency with which a surface exchanges thermal radiation with its environment. High thermal emittance enhances the ability of a surface to stay cool in the sun. The thermal emittance of a bare metal surface is initially low, and often increases as it is soiled or oxidized ( 4 ) . The thermal emittance of a typical non-metal surface is initially high, and remains high after soiling ( 5 ) . 5.3 This practice allows measurement of the solar reflectance and thermal emittance of a roofing specimen after the application of the simulated field exposure. 5.4 This practice is intended to be referenced by another standard, such as ANSI/CRRC S100, that specifies practices for specimen selection and methods for radiative measurement.