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Retroreflective coating for window blinds: Reconciling view, solar control and visual comfort

Publication Type:

Conference Paper

Source:

Facade Tectonics 2020 World Congress, Tectonic Press, Los Angeles, United States (In Press)

URL:

https://www.facadetectonics.org/papers/retroreflective-coating-for-window-blinds

Abstract:

Solar shading devices are required to find a trade-off between conflicting requirements: Protection from excessive solar gains and glare, daylight provision, and visual contact with the environment. Conventional shading devices using absorbing or reflective materials typically trade the protection requirements against the others, and therefore occlude the glazing. Retro-reflection of incident solar radiation towards the sky or the sun is an effective approach to the problem. The effect can be achieved in two dimensions, deflecting light to the incident elevation, but not azimuth angle, by prismatic structures forming either the profile or the surface structure of blinds. Achieving such shapes is elaborate due to the required precise processing of the louvers. Corner-cube structures applied as films to glazing have been demonstrated to achieve retroreflection in three dimensions (including the azimuth angle) of the invisible near-infrared portion of the solar spectrum, but only with the scope of moderating urban heat island effects caused by reflection from facades. In this paper a novel approach is described and a first feasibility analysis is performed to achieve retro-reflection through a coating based on micro glass beads (spheres) for application on standard blind materials of thin/regular geometry. The first prototypes of the coating turn out to be so effective that conventional spectrophotometric measurement (EN 14500) revealed to be useless, since it does not account for retro-reflection. This led to a completely new workflow including experimental measuring devices and modeling methods. The coating’s retro-reflection property was first modeled by raytracing and then by a data driven model obtained from gonio-photometric measurement. The coating models were applied to Venetian blinds, and compared to regular diffuse and mirror-like reflection in daylight simulation with Radiance. The preliminary results show the great potential of the retro-reflective coating to design shading devices that can control solar gains and glare and motivate further engineering, developments and validation.