In his classic treatises on architecture, 16th-century architect Andrea Palladio recommended that windows and doors be placed with the utmost attention to proportion and symmetry—“that the void may be over the void, and the solid upon the solid,” which, he said, “affords both beauty and cool air in summer, besides other conveniences.” Beauty, light, and air have always been the main objectives of fenestration—until now.
As the building community has embraced a more integrated and holistic approach to sustainability, a similarly sophisticated systems-based approach to fenestration has evolved, with building envelope and glazing technology becoming ever more energy efficient and dynamic. Windows are increasingly thought of as “transparent intelligent façades,” tasked with preventing heat loss, providing adequate daylighting, and contributing to higher overall energy efficiency or even net-zero energy buildings. Architects must now weigh a host of variables when specifying windows and doors—including glazing type, orientation, climate data, shading devices, HVAC systems, operability, and more—that would have made Palladio’s head spin.
Researchers, manufacturers, and architects are now engaged in important dialogues about how to make this process more integrated and user-friendly. Kerry Haglund, executive director of the Efficient Windows Collaborative and a former senior fellow at the Center for Sustainable Building Research (CSBR) at the University of Minnesota, is one such researcher, having presented at the annual BEST (Building Enclosure Science & Technology) Conference and elsewhere on the topic of fenestration. She says that architecture is moving into a new era, repudiating outdated approaches and “relatively short-term thinking” based on low costs or quick energy paybacks. When it comes to windows, she encourages architects to think more about long-term performance (read: 30 years) and to look well beyond aesthetics.
“Today, high-performance fenestration has to be designed to be integrated with the HVAC and the lighting systems to take full advantage of daylighting and occupant comfort strategies,” Haglund says. “These strategies need to be considered early in the design process, because they are not only part of the design and orientation of the façade but are also part of the design of the internal mechanical systems that provide appropriate ventilation, artificial light, and comfort to the building occupants.”
According to Haglund, a general design path for residential window specification might look like this: determining the window’s orientation, then daylighting controls (none versus dimming), then window area (window-to-floor ratio), then shading conditions (internal shades versus external or automated shading devices), and then, finally, window type. For the last one, the possibilities are seemingly endless, ranging from multiple layers of clear glazing to those with climate-specific low-E coatings on single or multiple panes of glass.
Stephen Selkowitz, a senior adviser in the Building Technology and Urban Systems division at the Lawrence Berkeley National Laboratory (LBNL), recognizes that the considerations have made things more complicated for architects, but that there are ways forward. He urges architects, contractors, and homeowners to literally push the envelope—to demand more from windows so that they make a house more functional, efficient, and comfortable, and perhaps even energy-producing, through photovoltaics. (He presented a paper on this subject at the BEST Conference in Kansas City, Mo., earlier this year.)
“For a building in a mild climate with small windows where the goal is to just meet the code, the solutions are relatively easy,” he says. “However, if an owner wants a highly glazed, net-zero solution in a moderate or harsh climate—and one that delivers comfort as well as net-zero energy performance—then that’s a real challenge not easily met by teams today. It requires a motivated owner and an integrated design approach that focuses on performance goals from Day One and wants to address occupant needs and practices in concert with the building design.”
For example, the amount of fresh air required in a building is generally determined by the expected peak occupancy rate and a fixed schedule. Yet we now have precise lighting controls that can detect occupancy on a much more granular level, even down to the desk or workstation of an office, for instance. This data can be shared with the HVAC system to determine ventilation requirements that are much more energy efficient and responsive to actual occupancy.
Selkowitz points to the New York Times Building near Times Square in New York City, for which LBNL was engaged to help design, evaluate, and specify an integrated solution with energy-efficient lighting and controls, automated shading systems, and an underfloor air-distribution system in what is essentially an all-glass building. In a 2013 report five years after occupancy, LBNL found the building had experienced 56 percent lighting energy savings, 24 percent total energy savings, and up to a 25 percent reduction in summer peak demand over a similar code-compliant building. Perhaps most importantly, occupants were generally satisfied with working conditions there and the operation of the “smart shading and lighting” solutions.
Technology and simulation become essential to these kinds of success stories. LBNL has developed two simulation software tools, RESFEN for residential applications and COMFEN for commercial ones, which give decision-makers useful information on the impact of various design variables, including U-factor/R-value, solar heat gain or shading coefficients, and context conditions. The Efficient Windows Collaborative, a joint effort between the Alliance to Save Energy and the CSBR, has developed two easy-to-use online tools for windows: A residential Window Selection Tool (efficientwindows.org) that is geared toward homeowners, and the Façade Design Tool (commercialwindows.org), structured more for the designer or architect.
Simulation tools have already made an impact on built work. For SERA Architects in Portland, Ore., the firm’s residential work is typically urban multifamily housing ranging from 60 to more than 200 units. Because of many shared internal walls, fenestration in the exterior must be optimized, according to the firm's Sustainability Resources Group manager, Mark Perepelitza, AIA. “We balance the needs for daylight and views with heat loss and gain,” he says. “For some projects we check scenarios in energy modeling tools, including COMFEN, to compare window and glazing configurations. The R-value of the fenestration assembly has a significant impact on winter heat loss.”
Designers must strike a balance between managing solar heat gain without compromising transparency. “One option is to select different glazing based on solar orientation,” Perepelitza says, “but for elevations oriented toward the south, horizontal shading is a great option because it can block high-angle summer sun while allowing low-angle winter sun.”
Perepelitza points to the firm’s Burnside 26 project, a four-story wood-framed residential building that opened in Portland last year. The building uses low-E glass coatings that were specifically selected based on solar orientation; but because the color difference is so subtle, Perepelitza says, the different glazing had no adverse impact aesthetically. “An integrated design process allows us to optimize energy, health, and comfort with visually compelling buildings,” he says. “We have a good handle on the fundamentals—but there are still plenty of challenges and opportunities to push for even better performance.”
At LBNL, Selkowitz’s team is now convening a consortium of businesses around the new Active Integrated Perimeter Building Systems project. The team is tasked with creating an infrastructure for fenestration in which hardware and software are all seamlessly configured and operate efficiently to meet energy and comfort goals under all use and climate conditions. It’s an ambitious goal, but one that Selkowitz is confident the team can achieve. “There is a lot of skepticism that these high-tech approaches can reliably work in buildings,” he says, “and, realistically today, often they don’t. Simply put, if we have the engineering infrastructure to create and deliver driverless cars, why can’t we reliably deliver a building that manages shades, lights, and HVAC to achieve low-energy goals and keep occupants comfortable?"