Page 114 - Designing for Zero Carbon - Case Studies of All-Electric Buildings

CASE STUDY NO. 5 SFUSD CLAIRE LILIENTHAL MIDDLE SCHOOL
(Opposite Page) The build- ing features large arrays of operable windows for cross- ventilation and daylighting. The gymnasium utilizes trans- lucent wall panels and tubular skylights to daylight the space. (Photos: © Technical Imagery Studios)
Building Envelope
The first step in meeting the lower EUI target was to add more insulation to the exterior walls and roof. Light gauge metal framing is used in the wall construction, creating the potential for some thermal bridging, so a continuous layer of rigid insulation (R = 4) is applied over the entire exterior wall surface. The wall cavities are filled with batt insulation (R = 21), bringing the total R-value of the walls to R = 9.8, which includes the effect of thermal bridging. The rigid insulation on the roof is overlaid by a single-ply membrane, bringing the roof structure to R = 31.
The substantial window area, utilized for daylighting and natural ventilation, has dual pane in- sulated glazing units that have a low-e coating.2 The frames are thermally broken: U = 0.45 and SHGC = 0.31. In addition, the windows on the south façade have custom exterior solar shading devices.
Daylighting and Electric Lighting
Daylighting has been a topic in school design for decades because of the perceived positive impact of glare-free natural daylight on learning. For the purpose of this case study, however, the focus is on the effect of the daylighting design strategies on reducing energy use. For the gymna- sium, extensive clerestory lighting from two directions is provided by a translucent building panel system.3 Several large tubular skylights4 are utilized in the gymnasium to augment the clerestory panels by bringing controlled daylight into the middle of the large room.
For the classrooms, tall windows for good daylight penetration are combined with automatic day- light controls and occupancy sensors to minimize the need for electric lighting. The issue of pre- serving the maximum roof area for the installation of the solar PV panels essentially eliminated the possibility of utilizing the tubular skylights above the two-story classroom wing. Daylighting was limited to the side lighting provided by the tall classroom windows and the interior high win- dows in the wall to the common area between the classroom wings. The second floor common area is daylit by a number of the tubular skylights and some of that daylight is captured by the adjacent high windows of the interior classroom wall.
Natural Ventilation
A substantial portion of the window area is operable, allowing cooling breezes to provide much of the required space cooling in this mild climate.
2 Solarban 70 by Vitro Architectural Glass, https://www.vitroglazings.com/products/low-e-glass/ solarban-70-glass/
3 Kalwall, https://www.kalwall.com/kalwall-products/
4 Solatube Skyvault commercial skylights, https://solatube.com/commercial
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Designing for Zero Carbon: Volume 1