Page 96 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 10
WEST BERKELEY BRANCH LIBRARY
84
Zero Net Energy Case Study Buildings: Volume 2
PHOTO: DAVID WAKELY
Daylighting and Electric Lighting
Daylighting is intended as the principal design strategy for reducing overall energy use in the building, which is accomplished by offsetting the normally high electric load for lighting the book stacks and reading areas. To emphasize this intention, the ceiling plane in the main public space is designed as the principal architectural feature as well, with the diffusing surfaces below the skylight arrays forming a variety of daylighted surfaces canted at different angles to spread the diffuse daylight to the large space below.
The electric lighting design for the space is meant to reinforce this design concept as well. The thin LED strip lights mounted to the tops of the bookstacks are designed to provide all necessary task lighting when the daylight from the skylight arrays is not adequate. Similarly, LED reading lamps at tables provide the task lighting for the reading spaces. The appearance of the space in the evening would be quite different than during the day, to a degree unconventional in modern lighting design but perfectly adequate functionally. This design approach also avoids the visual distraction away from the daylighting design feature that would be caused by a conventional design of ceiling-mounted or large suspended electric light fixtures, drawing the eye to the plane of lighting below the skylights. A client-directed modification to this lighting design approach was made during the construction phase—see the discussion in Post Occupancy: Lighting, p. 28.
Internal spaces in the library (staff area, teen room) are designed with separate skylight groups that are positioned adjacent to internal walls so that these wall planes become diffuse sources of light to these spaces. Other smaller spaces, located at the perimeter, have high clerestory windows abutting the ceiling for the same lighting design effect.
The design process for daylighting followed steps similar to other case study projects: the roof- scape was carefully studied for the integration of the skylights and solar panel arrays since the roof area is limited and number of solar panels had to be maximized. The layout of these features was also constrained by the Berkeley Fire Department’s requirement to leave a four-foot wide walking area around the edge of the roof itself. The daylighting design for the spaces below determined the basic location of the skylights and the solar panels were fit to the remaining al- lowable area.