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Smart Shades
A very important part of a Living Building is a living “skin”; a selective filter that responds to the ambient environment to maintain comfortable conditions inside the building. In the case of the Bullitt Center, the windows and shading systems do the bulk of the work for the daylighting and ventilation, as well as assisting in the thermal comfort of the building.
The skin is a system of layers that are used in different combinations to achieve optimal thermal and daylight qualities. The outermost layer of the skin is the deployable stainless steel shades. Designed by Warema, the system sits about 12 inches away from the windows. In the summer, when solar heat gain can be a challenge, the shades deploy to scatter direct rays before they hit the glass. In the winter, the shades are designed to maximize natural daylight in the office spaces, while still protecting against direct glare on workstations.
Smart shades
Electric Lighting
Daylight will illuminate the interior of the Bullitt Center for 90% of the time without the need for electric lighting. Keeping electrical lighting at a minimum to reduce energy use was a design driver throughout the process. The lighting design incorporates simple lighting controls: manual dimming, occupancy sensors, photocells, and plain old wall switches.
In some areas of the building an occupancy sensor turns the lights on and off, and in others the occupant switches the lights on and an auto control will turn them off. The circulation spaces use carefully placed wall washing light fixtures, which dim to 50% after a programmed time and then turn off after another set time, to guide people with areas of strong vertical illumination. The lighting in the stair area is monitored by an occupancy sensor, allowing the lighting to “follow” the person as they move up and down the stair, turning off the fixtures when the stair is unoccupied.
Tenant spaces will use task lighting to augment the daylight to keep the lighting power densities very low, with minimal need for ambient lighting. Occupancy sensor power strips located at each desk keep lights and computers off when the desk in unoccupied. Simple systems like this and “green switches” to turn off power to the floor at night help eliminate phantom load of systems that typically run all night. Occupancy sensors turn off emergency lights after hours and all external building entries have motion sensors so when there is no foot traffic the building can fall truly dark.
The core building control system is a DALI (Digital Addressable Lighting Interface) system, allowing flexible control of individual fixtures and modularity in the future expansion of the system.
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Daylighting Test
In order to minimize the energy consumption on electrical lighting, daylighting is well introduced in the Bullitt Center. Before construction, a daylighting simulation as shown in Figures on the right. Side windows and skylights are applied in this building to maximize the daylighting. As we can see, most indoor spaces have sufficient daylighting, but the places near the windows are too bright. To avoid the glare caused by daylighting, further work has been down. Three work stations including the west station, northwest station and southeast station are chosen to test the luminance.
As we all know, the most acceptable illuminance for human being is about 350 lux. However, the midian illuminance of the entire floor plate of the Bullitt Center is recorded by the system under different conditions during a day. In a clear sky day without blinds, the illuminance far exceeds the appropriate illuminance range and the conditions in a overvast day or a variable transmittance glazing are not as good as that under the condition of clear sky day with blinds. Consequently, window with blinds is recommended after measurement.
The median illuminance of the entire floor plate of the Bullitt Center
The daylighting simulation (DF) of the Bullitt Center (standard floor).
The daylighting simulation(DF) of the Bullitt Center (atrium).
Lighting Control System
The comparison of different sun control systems
The light redirection systems
Several lighting control systems are applied in Bullitt Center. As illustrated in Figure s on the left, the date of simulation is on December, when the climate of Seattle is cold and sunlight is needed. The pictures show the workstation without sun control, with automates electrochromic windows and automated exterior venetian blinds. Obviously from the color display, the window without sun control has glare and the window with automates electrochromic has almost no sunlight, both of which are not appropriate. Therefore, the window with automated exterior ventian blinds is the best that sufficient daylight get access into the working space and cause little glare.
What’s more, the weather responsive switching and solar shading is also used in the Bullitt Center. In cloudy day, the optimum transparency state is on so that the soft daylights are able to get into the indoor area while in sunny day, ECW Shading State Via Controls are on with blinds to stop the glare and provide shading. Occupants could adjust the control of heating and cooling according to thier preference with manual control.
The above mentioned sun control system is for side windows. As for the skylight, the light diffusion system is applied in Bullitt Center.
The lighting diffusion system in the Bullitt Center
A spectrally selective switching and intensity control system is introduced to control the light diffusion in space with skylight. This diffusion system is made of PVB, which has the function of Tvis Control or darkening. In light of the different wavelength in the atmosphere, the diffusion allowed the selected wavelength to get through. For example, the wavelength in a sunny day is longer than 550nm and as a result, it is not able to pass the diffusion. However, in a cloudy day, a wavelength shorter than 550nm is allowed to get through the diffusion and diffuse the light in the interior space. Hence, the diffusion control system could select suitable wavelength and harvest the energy by optimizing the insolation control.