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Automated roller shades

Automated roller shades manage daylight, solar heat gains, view, glare, privacy, and building appearance through changes in shade height. A roller shade consists of a fabric wrapped around a horizontal tube, which contains a tubular motor. The tubular motor rotates when ac- or dc- power is applied to it causing modulation in shade height. The control system can be designed to optimize numerous variables, the most common being control of direct sun. In this application, the shades were controlled to five preset heights that aligned with the architectural features of the façade — i.e., the vision portion of the window wall — so that direct sun penetrated no more than a specified distance from the window wall. The Times Company also requested that the shades control window glare, yet maximize the opportunity for view and daylight admission. Unnecessary up/down movement of the shade was to be minimized. Fabric choices (openness of the weave, color of the fabric facing toward the interior and exterior) were additional considerations in terms of appearance as well as visual comfort and daylighting benefits.

Two systems were evaluated in the mockup:

  • In Area A, a prototype shading system using an interior ceiling-mounted sensor was used to manage window glare, daylight and view.
  • In Area B, a motorized shading system that has been on the market for 30 years was used initially to manage direct sun then later to also manage window glare.
Time-lapse images of shade on February 23, 2004. View of southwest corner looking west Time-lapse images of shade on February 23, 2004. View of southwest corner looking southwest Time-lapse images of shade on February 23, 2004. View of west façade near center of the mockup dividing the two Areas – shade operations will differ between the left and right sides of the window wall.

Time-lapsed images of shade on February 23, 2004 in the daylighting mockup. Left: view of southwest corner looking west; middle: view of southwest corner looking southwest; right: view of west façade near center of the mockup dividing the two areas — shade operations will differ between the left and right sides of the window wall. Click on image to watch time-lapse movie.

Controlling roller shades to manage direct sun and glare reduces interior daylight levels, lighting energy savings, and access to view. Each of the manufacturers used different sensing and shade control approaches in the mockup resulting in some noticeable performance differences. The roller shade fabric under consideration had an openness factor of 3% with an associated visible transmittance of about 6%. The shades were woven with two colors: the white surface faced out and the gray surface faced inward. In initial meetings, LBNL discussed alternative interior shade design options with the Times Company so that daylight would not be compromised in order to control glare.

The low sun angles of the southwestern exposure caused the worst-case situation for glare. The Times Company was able to immediately assess the glare from the low winter direct sun early on in the mockup and discuss options with the manufacturers, the architect, and interior design team. Monitored data revealed that glare from either the solar disk or from the shade backlit by direct sun would be a significant problem for some viewpoints within the space. Glare from the bright sky would also be a significant problem for some viewpoints (however, most of the primary tasks are conducted with the occupant facing away from the window). To control this glare, adjustments to the control of the shades were made and alternate shade fabrics were considered. In the final building, the systems were tuned to the specific requirements of the occupants and work groups, window orientation, and degree of obstruction and/or daylight reflection from the urban surroundings. Throughout the building, a wall-mounted manual override touch screen enables occupants to override the automated shade control system.

The Times Company clearly preferred the brighter daylit space compared to the darker, less daylighted spaces that most currently work in, citing the potential health benefits of daylighting. They found the quality of daylight to be palpably different in the morning versus the afternoon and were delighted with the subtle shifts in color, intensity, sparkle, and mood throughout the day. The rise and fall of the automated shades tuned their awareness to the varying outdoor solar conditions.

Actual savings and occupant satisfaction resulting from the system installed in the final building were evaluated in a post-occupancy study conducted five years after initial occupancy. Results from this study are given here.