ASTM E1980 Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surface

ASTM E1980 Introduction

ASTM E1980 is one of the most critical test methods to determine the solar reflectance properties of building materials and surfaces. It measures the combined effects of solar reflectance and thermal emittance, which is a way of depicting the surface temperature and energy performance. The results help the manufacturers efficiently test the opaque surfaces with measures to reduce heat buildup while operating in extreme temperatures. It finds application in reliability checks, performance evaluation, and specification purposes.  

What is ASTM E1980 Analysis?

ASTM E1980  is widely used in various fields, particularly construction and environmental engineering. This practice covers the computation of the Solar Reflectance Index (SRI) for opaque, horizontal, low-sloped surfaces under standard conditions. This method is intended to calculate SRI for surfaces with emissivity greater than 0.1. Testing for SRI, or solar reflectance index testing, measures how much solar energy a material can reflect and how hot it will get in the sun.

Scope of ASTM E1980 Analysis  

Surface solar reflectance and thermal emittance are crucial factors that affect surface and near-surface ambient air temperature. It can be measured using ASTM E1980. Surfaces with low solar reflectance absorb a high percentage of incoming solar energy. Meanwhile, surfaces with lower emissivity cannot radiate energy into the environment, causing them to heat up. The solar reflectance and thermal emittance are used to calculate the Solar Reflectance Index (SRI). Manufacturers and designers utilize these quantities to select suitable materials for creating energy-efficient products.

Principle of ASTM E1980 Analysis

Solar reflectance and thermal emittance are two of the most significant factors significantly impacting the surface and near-surface ambient air temperature. Low solar reflectance surfaces absorb a large portion of the incoming solar energy. Some of this absorbed energy is conducted into the earth and buildings, some is transferred to the air at higher temperatures through convection, and the rest is reradiated to the sky. For the same conditions, the lower the emissivity of a surface, the higher its steady-state temperature. Low emissivity surfaces cannot radiate efficiently to the sky and become hot. 

The determination of solar reflectance and thermal emittance and their calculation concerning the relative black-and-white reference temperature on surfaces may help designers and consumers decide on suitable materials for making buildings and communities energy-efficient.

Test Procedure of ASTM E1980

Researchers calculate the Solar Reflectance Index using solar reflectance and thermal emissivity for three convective coefficients: 5, 12, and 30 W·m–2·K–1, corresponding to low, medium, and high wind conditions.

ASTM E1980 Specimen and Data Analysis

The ASTM E1980 standard practice report should contain the following information:

The test surface’s solar reflectance, thermal emittance, and the calculated SRI for three convective coefficients. The values are in SI units and are considered standard.

ASTM E1980 Test Conclusion

The ASTM E1980 analysis provides a much-needed, reliable, standardized way of evaluating the accelerated aging behavior of materials under controlled environmental conditions. The technique allows for long-term performance and durability prediction by simulating various aging processes, such as temperature and oxidation. The knowledge acquired from the ASTM E1980 test results is essential in making decisions on material selection. Furthermore, it ensures quality assurance and designs products with a long life expectancy.

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