Scheduled to be occupied by 2004,
this 289,000 square foot office building sits just southeast of an older 16 story
building owned and occupied by the same client in downtown San Francisco. LEED
certification has been a goal for the owner since the start of the project and
the design team has taken performance issues seriously from the initial design
stages of the project. We joined the team early in the schematic design process
and worked through construction documents as daylighting, shading, glazing and
alternative energy consultants. On this project our role in the Value Engineering
meetings was critical for the integrated curtain wall/daylighting/mechanical strategies
to retain their components and performance. The building is 12 stories
tall with an angled northwest window wall that reduces the area of the floor plates
as the building goes up, admitting daylight into the plaza created between the
two buildings. Due to the street grid south of Market in San Francisco, the elevations
are oriented off the cardinal to the NE, SE, SW and NW. The constricted site and
need to maximize usable floor area led to a large, rectangular building plate
(average of 140 feet by 184 feet) with a central core. This leaves deep 54 foot
office bays to be sidelighted as much as possible from only one side on the northwest
and southeast and narrower bays on the southwest and northeast. Recognizing site
height restrictions, the floor to floor dimension is 13'-9" with a 9'-10" floor
to ceiling height to accommodate deep beams for the long spans. The design
team undertook a serious attempt to maximize daylight and comfort in the office
floors in spite of the relatively deep plan and low ceiling height. We used extensive
DOE2 parametric modeling early in the schematic design phase to quanitfy the impact
of curtain wall designs, glazing specifications and mechanical strategies. These
studies enabled the mechanical design to optimize the underfloor air distribution
design, with a ceiling plenum is used for the return air. Thermal modeling convinced
the team that perimeter reheat could be dropped from the mechanical design if
the curtain wall design was changed to improve the U-value of the glazing and
the spandrel panels were more heavily insulated. If necessary, local reheat units
can be dropped in to solve an individual comfort problem once the building is
occupied. On the southeast curtain wall, light-redirecting glass (Serraglaze)
was modeled and then specified for the clerestory glazing. Tests demonstrated
that this would deliver daylight much farther into the office plan than usually
achievable with a simple high clerestory design. Work with various glass manufacturers
and suppliers determined that we could economically, and in a time sensitive job,
specify this material for the first U.S. architectural application. To improve
the visual quality of the workspace, the column line was moved back from the window
wall the ceiling at the perimeter and the deeper office space is daylight with
reflected light from a combination exterior overhang and interior light shelf.
We worked to size and detail the overhang and light shelf to work together to
block direct sun penetration through the clerestory glass. The view glass will
be shaded with manually controlled diffuse roller shades as desired by the occupants.
On the northwest slanted curtain wall, the low angle sun penetration during
summer months poses a [rpblem of visual comfort. After reviewing a number of options,
we recommended the use of OkaSolar in the clerestory light. OkaSolar is imported
from Germany (information is available for the United States at http://www.us.schott.com).
This product is an integrated louver unit designed to redirect direct beam radiation
toward the ceiling rather than allowing it to penetrate deep into the office floor.
A tracked roller shade will then be used on the view glass to control sun penetration.
Although quite expensive, the OkaSolar is specified for just the northwest elevation
clerestory where it is the highest performing glazing for the task. The total
cost is very small within the overall building budget. The shorter northeast and
southwest curtain walls do not have to deliver daylight as deeply as the other
two elevations. However, shading is still serious issue on these elevations. We
helped the architects to design deep horizontal grates as exterior overhangs and
suggested a strategy of assigning interior spaces tolerant to direct beam radiation
to these areas. We were also asked to develop recommendations for the use
of PVÕs on this downtown, mid-rise building. We provided the team with recommendations
as to the type, area and location of the PV arrays which would best balance cost
and performance in this difficult urban site. In addition, we are working with
the design team to explore the use of an underground river for heat rejection. | 
