Case Studies: Cambria Office Facility

L. Robert Kimbal & Associates

Buildings and occupants rely ever more on mechanical services. Traditionally, a building's basic structure accounted for about 80 percent of its costs. With the transition to skeleton frame structures over the last hundred years - as opposed to load-bearing masonry - that cost has fallen to some 20 percent. On the other hand, the cost of building services has ballooned, with mechanical systems typically consuming 35 percent of the building budget. Today, more is spent on services than on any other building component.

We place tremendous importance on environmental comfort, leading to these profound changes within building expenditures. But these broad distinctions between costs for a building's basic structure and mechanical services do not sufficiently address the interplay between building components. Structure, which encompasses envelope, impacts services. For instance, consider Pennsylvania's Cambria Office Facility in Ebensburg, where investment in a high-performance, triple-glazed window system eliminates the need for perimeter heating - reducing mechanical system first costs, to say nothing of operational energy.

The project, a 34,500-square-foot facility, constructed for and leased by the Commonwealth of Pennsylvania, was designed utilizing a systems-integration process to minimize redundancies and maximize efficiencies. Triple glazing cost about $15,000 more than double-glazed windows. However, with triple-glazing, a perimeter heating system, priced at $25,000 , was not needed. Beyond this, the triple glazing had other advantages:

• The project air-conditioning system was reduced from 120 to 60 tons, saving $40,000. A tight, well-insulated building envelope, attention to daylighting, and other factors contributed to these savings. But project engineers and architects calculate that about 25 percent of this reduction—15 tons or $10,000—is attributable simply to better, more energy-efficient windows. The triple glazing saved capital costs associated with the HVAC system.
• Regarding comfort, the standards for this building require that the interior surface temperature of the windows remain 62 degrees Fahrenheit or higher when the exterior temperature is 20 degrees Fahrenheit. Triple-glazed windows meet this requirement. Though not a prime issue with this project, triple glazing is also very resistant to sound infiltration. Triple glazing also limits condensation. With their warmer surface temperatures, less moisture forms on triple-glazed windows.

Glazing innovations and shading or light redirection elements can reduce electric lighting needs and their associated mechanical loads. However, daylight never totally supplants electric lighting; rather, the glazing and envelope help daylight complement the electric lighting. Lighting fixtures are needed when there is insufficient daylight or for night occupation. The Cambria project also illustrates designers using triple glazing in concert with traditional daylighting strategies, to achieve energy consumption goals. The project is oriented longitudinally along an east-west axis, to maximize south and north exposures. Light shelves on the south-facing windows provide shade and reflect light inside, with an ultra-reflective ceiling driving daylight into the building. Roof overhangs shade second-floor south-facing windows to reduce cooling loads. Clerestory windows over the center of the second floor provide daylight from two directions, which increases daylight and distributes it more evenly to reduce glare.