Abstract
More and more attention is being paid to the solar reflectance of built-up surfaces due to its influence on the summer heating of buildings and urban areas and the consequent effects on energy needs for air conditioning, as well as on the peak load of the electric grid. Several standard test methods are available for measuring solar reflectance in the laboratory or in the field, based on different devices and approaches. A convergence of some methods has been achieved by rating programs in the U.S. and, more recently, in Europe and other areas. However, laboratory or field measurements are impractical for characterizing a large number of urban surfaces—whether it is for identifying critical issues, developing policies, or verifying compliance with building requirements. In this regard, satellite remote sensors have recently become available, through which it is possible to estimate the reflectance of roof and pavement surfaces thanks to a spatial resolution that is suitable for identifying and characterizing individual built-up surfaces. In the present paper, the most-used standard test methods for rating of solar reflectance are reviewed. Subsequently, some publicly accessible satellite sensors are examined, through which comparable measurements could be obtained.
Highlights
A spectrum used in the U.S for various purposes was specified in the ASTM E891 standard [38], whose first release dates back to 1987. This is the one initially recommended by ASTM E903 in its 1996 version, and it was adopted by the Cool Roof Rating Council. It is specified for air mass 1.5, beam normal solar irradiance and hazy sky at the latitude of the U.S It was probably intended for sun-tracking photovoltaic panels, so it may be a less appropriate choice while considering the thermal behavior of a built-up surface irradiated by the sun
Rating programs for solar reflective materials have converged on the use of spectrophotometers according to ASTM E903, or solar spectrum reflectometers based on ASTM C1549
Textured or profiled surfaces, a pyranometer can be used according to ASTM E1918
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Measurements after accelerated ageing provide provisionary values of solar reflectance and SRI, which can be used for performance rating while other samples are subjected to natural ageing The adaptation of this method to European urban areas, generally more polluted than those in the U.S, has been recently investigated [26]. Laboratory measurements are, impractical for characterizing a very large number of urban surfaces, whether for identifying critical issues, verifying compliance with building requirements, or developing policies In this regard, aerial and satellite remote sensors have recently become available, by which the reflectance of roof and pavement surfaces could be efficiently assessed thanks to a spatial resolution adequate for identifying and characterizing single built-up surfaces. Exploratory results are briefly presented about the comparison between field and remote measurements on built-up surfaces
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