Longtime solar performance estimations of low-E glass depending on local atmospheric conditions

Abstract

In the construction industry, low-emissivity glass is used to improve both thermal efficiency and visual comfort by reflecting or transmitting thermal radiation. The solar optical performances of this type of glass are calculated using the ASTM G173 (AM 1.5) solar spectrum, the unique worldwide standard. However, the local atmospheric conditions of real sites around the world are different from those used to model the ASTM solar spectrum, originally created for PV deployment in North America in the 2000s. As the latter has an impact on the shape of the ground-based solar spectra, the real solar properties of the installed low-e glass can be different from those calculated in laboratory conditions and using the standard. In this paper, we provide a comprehensive, multi-years analysis of the solar performances of a complete set of low-e glass located on 12 sites around the world. Local solar spectra are modelled using local atmospheric data. This new study analyse the solar transmittance of low-e glass around the world. Our results show that the ASTM solar spectrum is appropriate for the majority of the selected locations. For some particular sites, such as buildings near the equator or located in cities with high atmospheric turbidity, the standard solar spectrum is not appropriate. For these sites, solar transmittance can vary up to 5% when compared to the ASTM standard. Consequently, this paper shows the necessity to include the impact of local atmospheric conditions on the performances of low-e glass.