Grating optical filters for smart windows: Materials, calculations and prospects

Abstract

Smart windows with advanced architectural glass coatings providing the comfortable daylight and thermal environment indoors are an important component to improve the energy efficiency of the buildings. Chromogenic and other materials potentially applicable for filtering the solar radiation are reviewed. They have a variety of mechanisms for changing the light transmission depending on change in the ambient conditions or under the influence of electric current. A smart window with additional function of angular filtering of solar radiation without using the blinds or other light redistribution devices is described. Such a window has an optical filter consisting of parallel non-transmissive (absorptive, reflective or scattering, including chromogenics) strips on two surfaces of the pane(s). The filter blocks the direct sunlight partially or completely in a preset angular range and transmits the diffused light providing comfortable day lighting indoors. Methods for calculating the geometrical parameters of the gratings considering the annual and daily change in the solar radiation, the location of the building and the window's azimuth are given. Calculated angular and temporal characteristics of the light transmittance demonstrate the angular selectivity of the transmission of a smart window with grating optical filter compared to a conventional smart window fully glazed with chromogenic glass. A comparative assessment of the potential of various chromogenic and other materials for the use in smart windows, as well as in grating filters for them, is carried out. The future prospects of the field are declared.