Graphic interface meshes engineering with architecture for greener buildings.
By Sharon Tregaskis
Clicking through an array of graphic icons, Nathaniel Jones, M.Arch. ’09, animates the images on a trio of 27-inch monitors in a fifth-floor lab in Rhodes Hall. He clicks on a spinning satellite view of Earth on the screen to his left, then on a map of the United States, and last on a town near Chicago. On the screen directly in front of him, animation turns an architect’s three-dimensional rendering of a geometrically complex house into a sundial of sorts. In less than 60 seconds, the time-lapse display—which incorporates cloud cover based on actual weather patterns in Chicago and even the building materials and room dimensions of the house—simulates the angle of the sun's rays as they fall on northeastern Illinois, tracing the sun's arc through the sky over the course of a year and mapping the shadows cast by the house and nearby trees. On the screen at Jones' right, a second 3-D rendering of the house turns red and blue as rooms heat and cool with the combined effect of sunlight and mechanical systems, while a collection of charts and graphs detail such corresponding data as interior temperature, the building's energy consumption, and even its carbon emissions.
Known as Sustain, the program simulating this hypothetical building's performance is the product of collaboration among Cornell faculty in engineering, architecture, and computer graphics. Their goal: promote energy-efficient building design and system engineering by giving architects access to robust, tailored simulations using an intuitive, user-friendly graphic interface early in the design process. The open-source program traces its roots to work begun by computer science professor Don Greenberg '55 CE, BCV '58, Ph.D. '68, when he was appointed founding director of Cornell's Program of Computer Graphics in 1972.
Computers were in their infancy when Greenberg—who also holds joint appointments in the College of Architecture, Art and Planning and the Samuel Curtis Johnson Graduate School of Management—joined Cornell’s faculty. Early on, he focused on how computer-aided design could integrate the fields to which he devoted his own academic training: architecture and engineering. In 1974, Scientific American put his pixelated rendering of the not-yet-constructed Johnson Museum—in the middle of the Arts Quad—on its cover to illustrate the value of computer graphics for siting studies. Greenberg had grand visions for what computer graphics could achieve in the realm of modeling and simulations to optimize energy efficiency. Yet despite the drive for efficiency motivated by the oil embargoes and resulting energy crises of that decade, architects and engineers were loath to incorporate the new technology as anything more than a drawing tool. Back then, simulations took too long and just weren’t that much better than what humans could do with pencil and paper. "The computational power wasn’t there," says Greenberg, who has spent the last four decades refining computer graphics applications in healthcare, entertainment, and even ornithology. "It was too difficult."
Today, cloud computing and parallel processing have transformed the pace at which even the most complex simulations can be executed—and with energy a growing concern, Greenberg’s vision for computer graphics at the intersection of architecture and engineering has regained favor. "I love animation and entertainment," says the Jacob Gould Schurman Professor of Computer Graphics, "but I really think computer graphics can be put to better use, such as to improve the environment and enhance medical imaging and device designs."
In 2008, the professor received pilot funding to develop Sustain from Cornell’s Center for a Sustainable Future (now the Atkinson Center) with assistant professor of architecture Kevin Pratt and professor Kenneth Torrance, his longtime collaborator in mechanical and aerospace engineering. In 2009, the trio parlayed data from the pilot project into a proposal and received a three-year, $1.83 million grant from the Department of Energy to further develop Sustain. (After Torrance died of a heart attack in February 2010, Greenberg and Pratt invited Brandon Hencey, an assistant professor of mechanical and aerospace engineering, to join them.)
The Sustain developers: (l. to r., front) CS Prof. Donald Greenberg, Arch. Asst. Prof. Kevin Pratt, and M.S. student Nicolas Savva B.A. '11 CS, Physics; (rear) MAE Asst. Prof. Brandon Hencey, postdoctoral researcher Zhao Dong, research support specialist Nathaniel Jones M.Arch. '09, research technician Dave Bosworth M.Arch. '09, M.Arch student Colin McCrone, and research support specialist Lars Schumann.
Buildings account for 40 percent of the United States’ overall energy consumption and 72 percent of its electricity usage, according to the Green Building Council. Enhancing building efficiency could slash future energy demand and the carbon dioxide emissions that go along with burning fossil fuels. But achieving that goal requires more than new materials and a boost in alternative energy production—it requires a smarter approach to the information flow among architects and engineers that yields our built environment, says Pratt, who also has his own design firm in Ithaca. Historically, architects have conceived beautiful buildings, then handed off their designs to mechanical and structural engineers, who do their best to create systems to heat, cool, light, and shade the interiors. "Architects really need to know about engineering—we need good simulation information about how our buildings will perform early in the design process," says the architect. "If you wait to involve the engineers, it becomes a post-rationalization project to make the systems as good as you can based on the decisions that have been already made."
Thus, while decisions about siting and orientation have a profound influence on energy consumption, they’re often immutable by the time engineers enter the equation. In that stepwise approach, engineers work within the parameters set by architects to guarantee comfort and functionality for a building’s eventual occupants; optimizing energy efficiency takes a back seat. "Sustain can give critical information to architects at the early design phase," explains Hencey. "Some buildings have this problem where one side is heating and one side is cooling, just because one side is in the sun and one is in the shade, so you’re using energy twice. How can you design the building so that doesn’t happen?"
An actual building simulation contains thousands of variables—from building orientation to window size and placement, as well as choice of construction materials and even landscaping and the relationships among existing buildings that provide shade and block winds. The Department of Energy’s legacy simulation program, EnergyPlus, has long been a valuable tool for understanding the influence of such features—but it works slowly and generates tabular results. Consequently, the program has typically been deployed by engineers, late in a building’s design, and not by architects intent on optimizing their design
for energy efficiency.
Sustain aggregates an architect’s rendering—in Google SketchUp, 3ds Max, or Revit—with U.S. Geological Survey topographical site details, National Weather Service data, and building materials information; uses sophisticated graphics algorithms to speed the analysis by EnergyPlus; and presents the results pictorially. "We understand information much better when we see it graphically," says Greenberg. "That’s important for input and output." Thus instead of requiring users to type in latitude and longitude for a building site, for example, Sustain’s default setting employs a series of mouse clicks on the spinning satellite view of Earth. Once a simulation is complete, users see the results in three dimensions—a color map for the temperature on different surfaces, for example. "You can see how warm or cold different surfaces are as time progresses," says Hencey. "You can play out the day and see how temperatures vary and the building behaves. Normally you would look at line plots. This is more seamless, not so manual."
In addition to graphical interfaces, the group has prioritized the development of algorithms to briskly extract the most relevant information from complex data. In his graduate and postdoctoral research, Hencey developed algorithms for online analysis of heating and cooling loads in existing buildings, using an electrical analogy for heat transfer. The work was a valuable foundation for his collaboration with Greenberg and Pratt. "You can take a very complex network that you would use to describe a building by directly using the geometry," he explains, "and then simplify that down to something that you can run very quickly."
Historically, the tools architects have used to design a building aren’t compatible with the tools engineers use to analyze energy demand and design heating and cooling systems. The Sustain development team has found a way to bring them together. Using tools and algorithms from the entertainment world—notably Greenberg’s work with Pixar, Dreamworks, and other animation juggernauts in Hollywood—the team has replaced trigonometric calculations with pixel analyses, for example to calculate solar insolation and shading. Meanwhile, Hencey has tackled methods to translate graphic representations of rooms into quantifiable data. "A building is just geometry—polygons," he explains. "How do you take a bunch of polygons and say, ‘This is a room separate from that room?’ It’s a very simple idea, but there’s no model out there. It’s a very active area of research: How do we come up with algorithms that are able to understand what humans just do naturally—speech recognition, recognize an enclosed space?"
To further speed their simulations, the trio has focused on parallel processing—instead of sequentially analyzing thousands of state changes as a building absorbs heat from the
(l. to r.) Lars Schumann, Colin McCrone, and Brandon Hencey collaborate in Sustain's rich visualization environment.
sun or a furnace generates heat, they’ve broken those calculations into sets that can be analyzed simultaneously by multiple, remote computers, which are then reassembled for meaningful results. "Ideally, you could get a hundred-fold increase by running 100 processors," says Hencey. "But the idea of applying these concepts to buildings—how do you break them down and things like that—is not well understood. Modeling these systems is ultimately an art. At some point you have to make assumptions to simplify enough that you can actually calculate things."
As a senior member of Cornell’s faculty, Greenberg has his pick of collaborators. He chose assistant professors for two reasons: he thinks of mentoring younger faculty as part of his job and, perhaps more important, it’s the best way to get things done. "My belief is that the risk-takers, the people really willing to stick their necks out are the very old or the very young," he says. "I’m still at the university because I love teaching and being with young faculty and students." He also aims to perpetuate the work he started with Torrance by weaving it into the university’s academic fabric. "My goal is to start an undergraduate major in sustainable design, teach a studio," he says. "If you do research, it ends up being dependent on individuals; when that person leaves, it goes away. If you bring it to the academic enterprise, it’s sustained."