Smart window with grating optical filter: Comparison with smart windows fully coated with chromogenic layer

Abstract

A comparative analysis is presented of a smart window with grating filter and a conventional smart window fully covered with switchable layer using the same chromogenic material in its colored and bleached states. The filter, formed by two thin-film gratings with alternating transmissive and chromogenic strips, has an angular-selective transmission of direct sunlight. Both gratings are sloped on the window plane at an angle to the horizontal, calculated taking into account the window azimuth to adapt to the solar trajectory relative to this window. The previously obtained calculation methods are modified and expanded, on the basis of which the temporal characteristics of light and solar transmittance, as well as direct and diffuse illuminance and irradiance indoors, of windows with two different southeast azimuths for June 15, September and December are calculated. The results show two main advantages of a grating smart window over a conventional one. Firstly, in active (colored) mode, due to angular selectivity of transmission it has self-adjusting light and solar transmittance throughout the day and year without using the daylight shading/redirecting devices, and in the bleached state, it has a higher transmittance. Secondly, by adjusting the transmission of direct sunlight, the filter transmits more than twice as much diffuse light in both colored and bleached states, thereby increasing indoor comfort in any season.