Conference Year

2014

Keywords

Roller Shades, Visual Comfort

Abstract

High performance commercial facades rely on fenestration systems in order to control glare and solar heat gains. Recent efforts have concentrated on developing efficient automated shading controls, linked with lighting and HVAC controls. One of the challenges is how to balance the need for daylight versus reducing overall energy use while ensuring comfort for the occupants seated near windows. This requires detailed knowledge of the solar optical properties of fenestration, which affect the transmission of solar gains and daylight. Currently, there is adequate information, databases and predictive tools for direct and diffuse transmission (and reflection) through glazing, using angular properties. However, there is less information on shading systems. Existing models for Venetian blinds, that have been studied extensively, provide information for light transmission and reflection as a function of surface characteristics and blind tilt angle. Advanced experimental and computational methods such as bi-directional distribution functions, have been used for detailed characterization of complex fenestration systems. Nevertheless, there are very limited studies on the solar-optical properties of roller shades, which are installed in most new commercial buildings. In most existing studies and simulation tools, the properties of roller shades are assumed constant and diffuse, ignoring direct-direct transmittance and angular properties. The only available semi-empirical model on this topic (Kotey et al., 2009) showed that roller shades properties may have strong direct components and angular variation, depending on the openness factor and the fabric color. These can affect the energy and daylight performance of roller shades, as well as their impact on glare. This paper first provides an overview of current approaches for modeling solar optical properties of roller shades, including advantages and limitations. Then, integrating sphere measurements were conducted to determine the detailed solar optical properties of different roller shade products. The results are compared to previous findings and will be used to provide useful information about direct-direct, direct-diffuse and angular properties of roller shades, depending on openness factor and color. The differences between measured and modeled properties are identified and discussed. Finally, the impact of detailed solar optical properties on energy use, daylight performance and glare is evaluated using annual simulation results for different fabrics, orientations and climatic locations (Miami and Philadelphia). The results of this study are particularly useful for a more realistic evaluation of the impact of shading on energy use and visual comfort.

3389_presentation.pdf (2261 kB)
Solar Optical Properties of Roller Shades: Modeling Approaches, Measured Results and Impact on Daylighting Performance and Visual Comfort

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