Concrete is durable, inexpensive and ubiquitous. But is it sustainable?
Yes, argues Hongxi Yin, I-CARES associate professor at Washington University in St. Louis. Though the manufacturing process emits carbon dioxide, those emissions are offset by the material's longevity and unique thermal properties.
"Concrete will last 100 years," explains Yin, an internationally recognized expert on green development. It also boasts a high heat capacity, or thermal mass. On a summer afternoon, concrete walls absorb the warmth of the sun, slowing the rise of interior temperatures. On a summer evening, natural ventilation releases the heat back outside, dispersing it into the cool night air.
"Ancient peoples used thermal mass, but we've ignored that potential," Yin says. "If you design it well, with the right systems and insulations, you can make a net-zero-energy concrete building."
Now that argument is being put to the test as students from the Sam Fox School of Design & Visual Arts and the School of Engineering & Applied Science prepare for Solar Decathlon 2017.
Sponsored by the U.S. Department of Energy, the biennial competition challenges university teams from around the world to design and build full-size, solar-powered houses. This year's event, which takes place in Denver October 5-15, will feature cutting-edge prototypes ranging from 650 to 1,000 square feet.
Winners will be selected on the basis of: design excellence and innovation; energy and water efficiency; and market potential. Each structure must be capable of running typical household functions using only global solar radiation. Any other energy sources, such as batteries or AC grid energy, must be offset by an equal or greater amount of energy produced.
At stake is $2 million in prize money.
"Architecture is about bridging the gap between concept and reality," says faculty project architect Pablo Moyano, senior lecturer in architecture in the Sam Fox School, who is leading the studio with Yin and faculty project manager Ryan Abendroth, also a senior lecturer in architecture. "In a typical studio, students can make impressive designs. But with Solar Decathlon, they actually have to build them.
"Students are exposed to the entire process, from conceptual design to construction and operation," Moyano adds. "That's a unique experience and a valuable lesson."
Though Denver is still six months away, Team WashU has been hard at work for nearly two years.
In fall 2015, Yin and Moyano offered the first of four semester–long studios. Students began by creating individual proposals, which gradually merged into a final design. They also investigated sustainable strategies for heating, cooling, and ventilation, looking for ways to reduce and/or offset energy consumption while still maintaining a comfortable, functional space.
"The trickiest part has been crystalizing four semesters' worth of design ideas into a single project," says Adam Goldberg, a dual master's candidate in architecture and construction management. "So much of the design world, and architecture education, is theoretical. Solar Decathlon forces you to really grapple with every detail and connection."
Meanwhile, computer science students, working under the direction of Chenyang Lu, the Fullgraf Professor in Computer Science & Engineering, have worked to develop a custom operating system for the house. Yin and adjunct engineering professor Tim Michels co-taught a course on building energy.
In all, more than 100 graduate and undergraduate students have participated so far. The budget of about $550,000 represents a mix of University contributions, external fundraising, and industry sponsorships.
"This is a research project," Yin says. "Our challenge is not to deliver one building. Our challenge is to create a transdisciplinary framework that will improve efficiency throughout the industry.
"Buildings account for up to 40 percent of energy consumption and carbon dioxide emissions worldwide," Yin adds. "To conquer global warming, we have to find ways of dealing with buildings in the most natural, most affordable ways possible."
Many of this year's Solar Decathlon entrants draw from a similar palette of design ideas: solar panels, green roofs, flexible floorplans, and sophisticated monitoring abound. Virtually all rely on light-frame wood or steel construction.
CRETE House, the entry by Team WashU, stands in marked contrast. The 995-square-foot structure, which will eventually serve as a long-term residence for scientists at Tyson Research Center, will be built from six large precast concrete panels. Oversized gutters will provide shade support, extending the living space outdoors. A water collection system and series of modular planters will support hydroponic gardening.
"Concrete has a lot of upsides," Moyano says. "It's resistant to fire, humidity, mold, and insects. It's resistant to extreme weather, such as hurricanes and tornados. It's durable. The main downside is weight. Concrete is heavy."
To counteract that weight, students have worked with the Precast/Prestress Concrete Institute—particularly its Midwest, Mountain States, Central Region, and Illinois & Wisconsin affiliates—to design and cast sandwich panels using Ductal, a new, high-performance mixture.
"Ductal is six times stronger than regular concrete," Moyano says. "This allows us to create panels that are thinner and about 30 percent lighter than standard precast concrete."
Perhaps most strikingly, the house does not contain a traditional HVAC system. Instead—capitalizing on concrete's high thermal mass—the house is primarily warmed and cooled by water coils embedded within the panels.
"It's a hydraulic system," Yin says. "The thermal mass radiates a uniform, comfortable temperature."
In the coming weeks, students will begin assembling CRETE House at Washington University's North Campus, and will spend much of the summer refining and testing its systems. Then, in late August, they will take the house apart, ship it to Denver, and assemble it again for the competition.
"Solar Decathlon is a big challenge, but also a great educational tool," Yin concludes. "Students integrate cutting-edge architectural research with structural engineering, electrical engineering, manufacturing, computer science, and biology.
"But the larger goal is to prepare students to face the future. How do we serve the community? How do we increase efficiency? And how do we help to solve global warming and environmental issues?"