WINDOW TECHNOLOGIES: Advanced
Automated Shading Systems
Sun control is fundamental for preventing overheating and diffusing bright sunlight. Yet while windows and sun-control devices are significant parts of the history of architecture, in the twentieth century there was a shift away from the sun-control and shading considerations with the advent of mechanical systems and the availability of inexpensive energy. A renewed interest in daylighting for energy as well as human benefits—as evident in the work of many architects today—recaptures the rich idea that windows and sun control are inextricably linked.
There has been increasing interest in automated interior and exterior shading systems due to the recent trend toward all-glass, fully-transparent facades. These automated systems are often integrated with the daylight control systems of a building to fully capture the benefits of reduced electrical lighting and improved occupant comfort.
Automated shading systems have significant potential to reduce energy use and improve environmental quality. For buildings with low-performance glass (e.g., single-pane clear), automated (and manual) shades can also increase thermal comfort by raising or lowering the effective surface temperature of the window wall during the winter or summer, respectively. The higher initial price of automated shades can be partially offset by these performance benefits as well as the reductions in HVAC installed capacity and ongoing HVAC maintenance costs, and decreased cost for furnishings replacement due to UV fading and degradation.
The shade material and location of the shade in the window wall dictates the degree of daylight transmission and solar heat gain rejection. Exterior shades reject more heat than interior shades. Between-pane shades perform somewhere between exterior and interior shades depending on the size of the glazing cavity and whether it is ventilated. For roller shades, daylight, solar heat gain transmission, view, and privacy can be controlled by the perforation of the shade, shade weave, changes in material over the height of the shade, and differences in shade material on the front and back surfaces. View is possible through a roller shade with an openness factor as low as 2%. The venetian blind has a second option for movement—tilt angle—that enables it to control daylight and allow partial view while fully blocking direct sun.
Automated systems often have wall switches or hand-held remote controllers so that individual shades can be controlled. Automated controls feature scheduling, direct sun control or depth of sun penetration, solar heating, glare control, daylighting, occupancy, response to HVAC operations, and limits on exterior shade operations, in the case of high winds, snow, or ice.
Lawrence Berkeley National Laboratory (LBNL) completed a study in which they evaluated the potential of advanced facades in managing peak energy loads. A majority of sources on this topic stress the potential of the building envelope in reducing energy use through the use of daylighting, solar heat gain control strategies, natural ventilation, and integration with HVAC and lighting systems.
As part of a multi-year project focusing on the performance of advanced glazing systems, LBNL tested a series of more advanced facade design strategies, including automated exterior and interior systems, under real sun and sky conditions. These studies serve as the basis for the development of models describing the optical and thermal properties for shading systems, including automated venetian blinds and roller shades.