Retroreflective Coating for Window Blinds

Reconciling view, solar control and visual comfort

Overview

Authors

Photo of Luca Papaiz

Luca Papaiz

Innovation Manager

Pellini SpA

Lpapaiz@pellini.net

Photo of Lars Oliver Grobe

Lars Oliver Grobe

Lucerne University of Applied Sciences and Arts

larsoliver.grobe@hslu.ch

Photo of Giuseppe De Michele

Giuseppe De Michele

EURAC Research

giuseppe.demichele@eurac.edu


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.

Introduction

Shading devices that control solar gains to prevent overheating in summer, and excessive admission of daylight that potentially causes visual discomfort and glare, significantly affect electrical energy demand for heating

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Background

Standard Shading: Specular and Diffuse Reflectivity

Regardless of whether they are installed outside, inside or embedded into the glass building skin, solar shading devices work by absorbing or reflecting solar energy

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Method

Development of Retro-Reflective Coating

Previous attempts to design retro-reflective shading devices have been based on the development of advanced geometric profiles or structures with highly specular materials, and have led to

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Data

Model of the Coatings and Simulated Light Scattering

The BRDF of the virtual retro-reflective model is shown in Figure 10. The two images show the portion of energy reflected from the

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Explanation

Initial Performance Assessment

The analysis on the calculated models of the retro-reflective coating shows promising results in terms of visual performance. The luminance distribution over the façade is reduced when compared

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Conclusion and Future Work

The preliminary results of this research indicate the coating’s potential to reconcile aspects that usually are in direct contradiction when it comes to shading devices, namely: visual contact to the

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Acknowledgements

Figure 7a is based on an illustration contributed by Peter Apian-Bennewitz, pab advanced technologies ltd., Freiburg. This research was financially supported by the Swiss Innovation Agency Innosuisse and is part of the Swiss Competence Center for Energy Research SCCER FEEB&D. Part of the coating development was funded by the European Union’s Horizon 2020 research and Innovation programme under grant agreement N° 768766 – Energymatching.

Rights and Permissions

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