Solar responsive building glazing: Experimental analysis of the impact of photochromic glazing on indoor thermal and luminous conditions

Abstract

The application of films on conventional glazing aims at increasing the glazing performance by reducing energy needs and increasing indoor comfort. Photochromic films in particular can alter their optical properties due to a chromatic change in response to solar radiation, allowing for reduced glare levels and solar heat gains. However, despite the potential of application, this refurbishment solution is still poorly explored. Therefore, the main purpose of this work was to experimentally evaluate the thermal and luminous performance of a double glazing with and without a photochromic film installed, using two office rooms in Lisbon as case study. An extended field experimental campaign was conducted simultaneously in both offices, where temperature, solar radiation and illuminance levels were collected. The key contribution and novelty of this research lies on the experimental assessment of the thermal and visual comfort conditions with the photochromic film under real-occupancy. Even though the photochromic film significantly increased the surface temperatures of the glazing, the indoor air temperature was not negatively affected, with an increase up to 14 % of working hours with comfortable temperature during the heating period. Illuminance levels on vertical/horizontal plane were reduced by 24/36 % in the presence of the photochromic film, when compared to the clear glazing without film, resulting in an increase of 7 % of working hours with useful illuminance during the heating period, and large areas in the office room with imperceptible daylight glare levels when facing the glazing system. The impact of the film was less noticeable during the cooling period.