Spectrally selective laminated glazing consisting of solar control and heat mirror coated glass: preparation, characterization and modelling of heat transfer

In this study, solar control coatings were prepared by sequential depositions of thin films of ZnS (40 nm)-CuS (150 nm) and ZnS (40 nm)-Bi2S3 (75 nm)-CuS (150 nm) from chemical baths on 3 mm thick commercial sheet glass. These were laminated to 3 mm thick clear glass or commercially available SnO2 based heat mirror coating of sheet resistance 15 Ω on float glass of 3 mm thickness using a poly(ethylene vinyl acetate), EVA, sheet of 0.36 mm thickness in a vacuum process at 120 °C for 30 min. In total, the thickness of the glazing was 6.35 mm. The glazings possess visible transmittance, weighted for D65 solar spectra and sensitivity of the human eye for daylight vision, of 36% or 14% with solar absorptance of 71% or 78% depending on the coating type, i.e ZnS-CuS or ZnS-Bi2S3-CuS-heat mirror respectively. The solar heat gain coefficient (SHGC) was evaluated for these glazings at exterior temperatures of 15 and 32 °C for an exterior convective heat transfer coefficient (hex) of 6-100 Wm−2 K−1 using a mathematical model. The model predicts the extent of reduction in SHGC through the presence of the heat mirror coating as a function of hex and hence helps to decide on the relative benefit, which may be derived through their use in different locations. Though the deposition technique mentioned here involves longer duration compared with vacuum techniques, it may be developed into a low throughput, low-capital alternate technology for small-scale production.