ASTM E1918-21 PDF

Overview

ASTM E1918-21 is the international standard test method for measuring the solar reflectance of horizontal and low-sloped surfaces in the field. Developed by ASTM International, this method addresses the importance of solar reflectance as a critical property influencing the temperature of sunlit surfaces and the near-surface ambient air. The standard utilizes an albedometer or pyranometer to provide reliable, field-based measurements under natural sunlight conditions for surfaces that are predominantly horizontal or gently sloped.

Solar reflectance-sometimes called albedo-is the fraction of solar energy reflected by a surface. Materials with high solar reflectance stay cooler under sunlight, potentially reducing cooling energy requirements and mitigating urban heat island effects. E1918-21 supports informed choices for building materials and infrastructure by enabling accurate onsite measurement of solar reflectance.

Key Topics

• Test Scope
  • Applicable to flat or low-sloped (tilt angle ≤ 9.5°) surfaces at least 4 meters in diameter or on each side.
  • Suitable for roofs, streets, parking lots, and other large, homogeneous exterior surfaces.
• Field Measurement Methodology
  • Performed when the sun angle to the normal surface is less than 45°, usually between 9 a.m. and 3 p.m. local standard time.
  • Measurements are made under clear, sunny conditions with minimal cloud cover or haze.
  • Instruments: precision albedometer or pyranometer with appropriate calibration.
  • Reproducible readings obtained by repeatedly measuring incoming and reflected solar flux.
• Apparatus and Setup
  • The sensor is positioned 50 cm above the test surface to minimize shading.
  • The minimum offset from the test surface edge is 2 meters.
  • Pyranometer or albedometer must be accurately aligned parallel to the surface while reading both incoming and reflected radiation.
• Data Reporting
  • Documentation includes test location, time, surface description, weather conditions, and all measurement values.
  • The average solar reflectance is calculated for each surface, with statistical analysis when multiple surfaces are tested.

Applications

ASTM E1918-21 is widely used in the following contexts:

• Building and Roofing Materials
  • Evaluating and comparing roofing product solar reflectance to support energy-efficient building envelope design.
  • Assisting in compliance with green building standards and codes that require cool roofs or reflective pavements.
• Urban Planning
  • Measuring pavement and exterior surface reflectance to inform heat island mitigation strategies.
  • Supporting the selection of surface materials in public works projects to enhance urban cooling.
• Research and Development
  • Field testing new materials, coatings, or surface treatments for their solar reflectance properties.
  • Validating laboratory results through real-world sun exposure data.
• Quality Control and Specification
  • Ensuring product performance meets project and regulatory requirements for solar reflectance.
  • Providing reliable data for manufacturers, architects, and facility managers.

Related Standards

For comprehensive material evaluation and field measurement of solar properties, the following ASTM standards are commonly referenced alongside ASTM E1918-21:

• ASTM E177 - Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• ASTM E691 - Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

Additional related documents and international standards may cover laboratory measurement methods, energy efficiency requirements, and solar reflectance specifications for various applications.

Keywords: ASTM E1918-21, solar reflectance, albedo, pyranometer, albedometer, field measurement, cool roofs, energy efficiency, urban heat island, roofing materials, surface reflectance, ASTM standards, building materials testing, solar energy.