Dual-grating smart window with vertically distributed transmittance to optimize indoor daylight distribution and solar heat gain

Predicting year-round daylight and solar heat gain using building simulation software is an effective approach to assessing indoor visual and thermal comfort. This study proposes a method for modelling and optimizing daylight distribution and solar heat gain in a room with a dual-grating smart window having angular-selective and vertically distributed light and solar transmission. This newly developed smart technology features a dual-grating optical filter consisting of alternating transmissive and non-transmissive strips that can be sloped on window surfaces to adapt to the Sun's trajectory and have different transmittances along the height of the vertical window for optimal indoor daylight distribution and optimal solar heat gain. The calculation methodology was validated by numerical simulation of the illuminance distribution for a conventional double-glazed window without coatings and for the same window with four types of grating coatings. The best distribution was demonstrated by two windows with an exponential increase in the absorptive strip widths along the window height from top to bottom (1) with preset minimum and maximum strip widths in the upper and lower zones of the window and (2) with a preset total area of all absorptive strips; the distribution was worse for windows (3) with an increase in the strip widths in an arithmetic progression and (4) with their uniform distribution; the worst distribution was shown by (5) conventional window.