Glazing for Energy Efficient Buildings: The Almost Forgotten Role of Angular-Dependent Solar Transmittance

摘要

Glazing for energy efficient buildings comprises multi-pane units with surface coated glass. According to today's standards, glazing is characterized by optical measurements at normal light incidence. Here we show that this prerequisite is grossly inadequate for common vertical glazing, in particular regarding solar transmittance and total energy transmittance (g-value). We present data on spectral and angular-dependent transmittance in the 300—2500-nm wavelength range for several types of glass samples with hard (tin-oxide-based) and soft (silver-based) coatings. Furthermore, we use standard procedures to compute g-values for triple-pane glazing embodying such glass and find that the g-value at 60° off-normal angle typically is as low as 65-68% of the g-value for normal incidence. This difference is essential for assessing the energy efficiency of modern buildings and highlights that the glazing's angularity must be accounted for.