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Gap Corporate Campus 901 Cherry

The complexities of designing the high performance facade for the State Compensation Insurance Fund ranged from coordination of disciplines (architectural, structural, mechanical, curtainwall, daylighting, electrical lighting and space planning) to cost and value considerations in value engineering and specifications. While the design and evaluation of a curtainwall system in relation to single performance critera (daylight, energy use, cost, lateral loads, etc.) is not necessarily difficult, resolving all performance criteria within the design process and timeframe posed significant challenges. To help resolve this complexity Loisos + Ubbelohde performed detailed comfort prediction calculations.

Five selected perimeter office bays were evaluated to predict comfort. For several curtainwall options comfort software was used to generate the predictions for multiple points within each 30'-0" by 30'0" bay. The grid of predicted PPD was then presented in a three dimensional graph of the space for each option. The results indicated that corner situations, with greater exposure to cool glazed surfaces, showed the greatest dissatisfaction, with greatest discomfort at nearly 25%. The office bays with a single curtainwall exposure showed discomfort peaking around 20%, which is still greater than the ideal of 5%. In comparing the curtainwalls,improved U-Value and Shading Coefficient consistently reduced the percentage of occupants who would perceive the space as uncomfortable, allowing the elimination of perimeter heating. This increased thermal performance was significant enough to be a factor in the selection of the curtainwall system, once all other criteria (cost, availability and explosion-resistance among them) were factored into the decision.

Graphs show comfort as a measure of distance from the curtain wall for three different glass & frame types.

In the final stages of curtainwall selection the analysis was further refined. At this point a different way to exhibit the data was chosen, one that placed a hypothetical workstation at a location near the glazing. This graphic showed the area of the building that would be effected by the perimeter zone. As the performance of the skin was increased this zone decreased. This analysis allowed the client to make an informed decision on the skin performance based on comfort in addition to energy use criteria.


“Occupant Thermal Comfort and Curtain Wall Selection” in Journal Of Building Enclosure Design, Summer 2006, pp. 32-34.
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“A Case Study in Integrated Design: Modeling for High Performance Facades” from Performance of Exterior Envelopes of Whole Buildings Conference IX International Conference Proceedings, Tampa FL, December 2004, pp. 1-18.
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Hellmuth, Obata & Kassabaum

San Francisco, CA


Advanced thermal modeling was used to predict thermal bridging through curtain wall.