Page 126 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 11
THE EXPLORATORIUM
• The “waffle” slab creates substantial areas for the installation of thick insulation within the pans between the two concrete floor surfaces, thus providing a good average R-value over the large area of the exposed building envelope;
• This insulation layer makes it feasible to install a highly energy-efficient radiant heating and cooling floor system, using the new waffle slab for the plastic tubing that carries the heated or chilled water throughout the building; (See Heating, Ventilating and Cooling Sys- tems, below.)
XPS rigid-foam insulation is installed within each “waffle” cavity, with the thickness varying from 8” up to a maximum of 14”. There is still substantial thermal bridging through the floor beams (“waffle slab” ribs), but the overall R-value for the entire floor, which is exposed to outdoor air conditions beneath the pier, is R-5. The waffle slab is also insulated at the edges with 1” of poly- isocyanurate rigid insulation (R-10) to prevent thermal energy loss at these edges.
Since the floor strengthening was required for the seismic upgrade, this solution was permitted because of the benefits toward the building’s goal of ZNE performance. The level of the floor was raised by this system and affected some of the historic details of the column bases (e.g., wheel guards had to be raised to maintain visual proportions at the column base).
The energy efficiency of the structure is limited in part by the lack of a tight seal of the entire building envelope, due principally to the historic preservation requirement that the walls be left to a large degree in their existing condition. The new addition at the end of the pier could be designed at a high level of energy efficiency, however. The new walls are rated at R-19, for ex- ample. Standard issues of glare control in the event space plus concerns about “bird strikes” at the clear-glazed surfaces were resolved using modern glass materials with frit patterns, though the glazing area near the observatory space retains clear glazing locally for functional reasons, to ensure good viewing of San Francisco Bay from that location.
Daylighting and Electric Lighting
The tall windows and roof monitors that are part of the original warehouse structure are actually ideal for daylighting the length of the extended building. While the color of the interior surfaces was changed to be neutral rather than the original white throughout, there is nevertheless a good level of daylight penetration to the interior, adequate to provide an ambient level of lighting in the hands-on exhibit areas. Exhibit designers expressed some concern about the amount of daylight that could affect the exhibit spaces, creating conditions of difficult adjustment. The daylight levels are generally a good match with the ambient level desired in the vicinity of the exhibit spaces, however, typically in the range of 0.5 watts/sq.ft.
An effective daylighting design strategy proved to be locating the regular staff office areas on a second-story mezzanine, close to the roof monitors, thus essentially raising the level of daylight available at the work surface level.
The electric light fixtures used for the exhibit areas were selected for their high efficiency. All electric light fixtures are digitally addressable for individual control purposes. There is no dim- ming of the lights in response to daylight; the primary control is simply on/off and is remotely programmed to scheduled use.
Natural Ventilation
Because of the restrictions on any changes to the historic features of the building, there is little opportunity to introduce design strategies related to natural ventilation for cooling purposes. However, the existing roof ventilators were restored and selected roof monitor windows were replaced with louvers to add relief air. These louvers are tied to a CO2 sensor and can also be mechanically operated to open when extra ventilation is needed.
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Zero Net Energy Case Study Buildings: Volume 2