Page 124 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 11 THE EXPLORATORIUM
Building Envelope
Historic preservation factors were the principal determinant for much of the building envelope. This strongly affected the design choices for optimal energy performance and achieving ZNE.
The walls are built of steel structural frames and 8” thick concrete panels—very thermally conductive materials and constructions with much thermal bridging. The exterior and interior appearance of these walls was deemed to be contributory to the historic character of the building, which required that no changes be made—specifically that no insulation layer with new finish could be applied. Single glazing could be replaced with high-performance double-glazed units, however, since the appearance was not noticeably different if the window frames were suitably replicated. (The exception to this was the glass installed at several loca- tions where industrial wire-glass was first used in 1931, an innovation at the time. These glass areas were required to remain as single-glazed wire glass units.)
The surface area of the walls is much less than that of the floor and roof, however, so thermal losses are actually dominated by the latter building surfaces. The interior surface of the roof structure and roof sheathing could not be disturbed because of its historic nature, so a second roof was created on the outside surface and a cavity between the two roofs was filled with insulation, bringing the roof R-value to a substantial R-28.
This solution at the roof greatly assisted with the building’s ZNE performance goal, but it also resulted in the need to raise the sills of the roof monitors because of the added thickness of the overall roof system. Fortunately, the governing historic agencies determined that the visual impact of this change was small enough to allow the installation of the insulating layer and replacement of the roof monitor windows with high performance assemblies.
The structural strengthening of the floor system and pier deck had more significant impacts on the historic structure. To provide a sufficiently strong structural floor diaphragm, a new concrete floor system of beams-and-slab, resembling a structural “waffle” slab system, was proposed to be installed on top of the existing concrete pier deck. This design provides an opportunity for an integrated solution for the historic preservation, structural and ZNE performance objectives:
• Thestructuralrequirementforasufficientlystrongfloordiaphragmissatisfiedwithaminimalimpacttotheexistinghistoric structure;
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Zero Net Energy Case Study Buildings: Volume 2