Sun, Shading and Glazing Controls

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Introduction

Photosensor control can also regulate the daylight entering a space. Photosensor control can be applied to settings of translucent roller shades, interior or exterior louvers or blinds, electrochromic glazing, or other daylight control devices. The challenge in these situations is the selection, placement and calibration of the photosensor that will control a shading device. In some cases, it is best to locate a photosensor on the exterior of the shades to sense the amount of daylight that would otherwise enter the space. Some systems also consider the position of the sun relative to a façade or daylight aperture. The solar position dictates how deep sunlight will penetrated into a space through clear glazing, as well as the blind angle required to intercept and block direct sunlight rays. Some systems apply computer software and an exterior shading object model (considering the surrounding obstructions like neighboring buildings) to determine when a particular window might be illuminated by direct sunlight. With sunlight angle control, roller shades may only be lowered to a position that limits sunlight penetration to a prescribed distance into a space. In some cases, thermal loads may also be considered in deciding how to operate shading devices.

Museums often require strict daylight control to limit the amount of daylight incident on works of art. In these situations, a photosensor mounted with a space or within a well on the interior side of a set of motorized blinds can be used to control angle of a set of blinds and thus adjust the amount of daylight entering a space.

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Lead Author(s): Rick Mistrick

Automation

The selection of window blinds and building occupants’ use of them may be the single greatest determinate of realized daylight performance in side-lit buildings. Blinds allow for the control of glare and the diffusion and re-direction of sunlight. They also enable occupants to provide privacy or darkening when required and offer thermal comfort control by blocking direct beam sunlight. Blinds can deliver high quality diffuse daylight when direct sun is present and can be retracted during overcast days or times when direct sun does not pose visual or thermal discomfort. However, this requires frequent adjustment to realize optimum performance. Too frequently, blinds are deployed to “worst-case scenario” position when momentary glare arises, and then remain in that position indefinitely causing the occupants to rely exclusively on electric lighting.

For this reason, some designers choose to incorporate automated blind systems. These systems allow for continuous adjustment of blind deployment and/or slat angle based on current weather conditions and sun position. Automated blind and fabric shade systems enable persistent daylight performance where continuous blind adjustment by occupants is impractical or impossible. Automation ensures that blinds are retracted when unnecessary to provide unobstructed views to the exterior and maximum daylight performance for the longest duration possible.

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Lead Author(s): Matthew Tanteri

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