Advanced Fenestration And Daylighting Systems

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Windows; Buildings


Advanced fenestration and daylighting systems form an interesting new class of devices and products for introducing natural lighting (daylight illumination) into buildings. They are split into two distinct classes. Advanced fenestration systems are new high-performance glazing and reflecting systems for otherwise conventional windows which offer specialized spectral and/or angular selectivity, intended for improved illumination quantity and quality while managing solar radiant heat gain to meet both human comfort and energy conservation objectives. These spectral and/or angular selectivities can be built into the glazings, incorporated into new objects placed between the panes, or they can be part of objects attached to the interior or exterior frames of the windows. The class includes a wide variety of fenestration attachment products, such as shades, blinds, screens, fixed and movable louvers, and even mirrored surfaces for re-directing the daylight entering fenestration apertures. This class also includes several novel new glazing types such as those containing electrochromic and holographic layers, still in the research stage. The second class of systems, advanced daylighting systems, includes those manufactured by a new solar lighting industry, whose products are targeted for what has been called "core daylighting" because they are intended to introduce daylight into the core spaces of multi-story buildings, spaces distant from the building envelope, or in other locations where more conventional daylighting apertures cannot be placed. Solar lighting systems include the widely available tubular skylights offered by many manufacturers in the U.S., Canada, and other countries around the world, and a variety of new systems just entering the market (or being prepared for future market entry). The distinction between solar lighting systems and more conventional daylighting systems is illustrated schematically in Fig. 1.Solar lighting systems are fairly recent innovations, and haven't yet experienced widespread use. Both categories include complex devices whose performances are difficult to predict and quantify for all locations and seasons. The difficulty of quantifying performance stems from the complex Figure 2. Between the panes and interior shades make for complex windows. nature of their angularly selective performances. The solar heat gain of spectrally selective clear glazing systems can readily be calculated with widely available computer programs. Spectrally selective materials which are also nonspecular in transmission and reflection, however, pose difficulties. In order to understand the difficulties encountered, with all the systems described herein, and better to understand how some of the more elaborate systems work, a few concepts of optical physics and of radiometry need to be understood. These include the definitions of irradiance, radiant intensity, and radiance, as well as their photometric counterparts, illuminance, luminance, and luminous intensity. An understanding of the fundamental optical properties of materials is also needed, including the biconical and conical-hemispherical transmittances and reflectances of sheet materials, both opaque, translucent, and completely clear. For comprehensive discussions of these quantities, the reader is directed to chapters 1,2, and 6 of a recent textbook on the subject1.

Date Published



Buildings - Windows

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