With the aim of reducing the cooling energy demand of buildings and limiting the urban heat island effect, the optical properties of building materials such as roofing and pavers are taken into account in the U.S. American LEED® Green Building Rating Systems. According to the ASTM E1980-11 standard, opaque roofing or paving materials which are installed horizontally or at a low tilt angle can be characterised by the so-called “Solar Reflectance Index – SRI”. It is calculated from the solar reflectance (SR) and the thermal emissivity, and is a measure for the relative heating of such materials when absorbed solar radiation and heat emitted to the atmosphere are considered. The paper illustrates why the SRI value of surface-covering materials is significant for urban climates. It will also present the derivation of the SRI value from measured reflectance spectra, SRI examples for concrete pavers of differing colours and correlations with other quanti- ties which can be derived from the reflectance spectra, such as solar and visual reflectance.
Fraunhofer-Institut für Solare Energiesysteme
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