Research Highlight UNC Charlotte's U.S. Department of Energy 2013 Solar Decathlon House
Date Published: April 13, 2014
After much innovative design and hard work, UNC Charlotte was proud to compete in the U.S. Department of Energy’s international Solar Decathlon held last October in Irvine, California. Ingersoll Rand, a founding member of SIBS, was also a major sponsor and technical advisor of UNC Charlotte’s Solar Decathlon student team.
The Solar Decathlon challenges collegiate teams to design, build, and operate solar-powered houses that are cost-effective, energy-efficient, and attractive. The winner of the competition is the team that best blends affordability, consumer appeal, and design excellence with optimal energy production and maximum efficiency.
The team’s UrbanEden house won third place in the prestigious Engineering competition and first place in the People’s Choice competition (story).
Work began on the design in October 2011. The UNC Charlotte team began construction of its solar house in March 2013 and completed the house in September before transporting it to California.
UrbanEden is a net -zero energy solar powered home designed for the city of Charlotte, NC. Envisioned as an urban infill project for a couple ("DINKs" or "empty-nesters"), the house design is defined by a strong connection between indoor and outdoor living areas; even in an urban context, the outdoor living area allows one to privately enjoy the outdoors. The house incorporates truly revolutionary approaches to sustainable design and construction, including the choice of primary building material (geopolymer cement concrete), an innovative active/passive hybrid cooling system integrated into the walls of the house, PV panels on adjustable racks, and responsive technology that allows the house and its inhabitants to adapt to changing environmental conditions. Its design begins with an ancient urban material, expertly modified to become an eco-friendly, innovative building material: pre-cast geopolymer cement concrete. Aesthetically versatile with its many possible surfaces, but always appropriate to a city setting, the concrete provides an effective sound barrier to the noise of the city. Outdoor living defines UrbanEden's design. The home's southern facade is completely comprised of high-performance glass, which fills the home with light and connects the interior rooms to a set of private outdoor rooms enclosed by a vertical garden that provides a peaceful habitat for flora and fauna, as well as herbs and vegetables for sustenance.
The house has been designed to incorporate natural cross-ventilation when the humidity and temperature are in an acceptable range. But even with all doors and windows closed, a vital connection to the outside is maintained through fresh air supplied by the energy efficient Energy Recovery Ventilator.
Concrete is a key innovation in UrbanEden's energy-efficient concept and structure. In state-of-the-art, high-performance housing it is common to combine high-mass passive solar design with thermal-bridge free, airtight building envelopes. However, the mass component is usually limited to an insulated concrete floor slab. In UrbanEden, the mass has moved to the walls in the form of insulated precast panels. This seemingly simple choice is, in fact, a major innovation. By markedly increasing the surface area and related volume of our thermal mass in the passive solar context, we have been able to implement a hybrid passive/active hydronic cooling system that, unlike conventional hydronics, uses only pump energy to accomplish temperature changes.
Embedded in our precast panels are arrays of small diameter plastic "capillary" tubes. In the summer, the concrete slowly takes on ambient heat from the interior space during the day. At night, water is moved through the capillary tubes to copper fin heat exchangers above the roof. The combination of the large surface areas of the interior wythe of concrete and the embedded tubes creates a very efficient transfer medium for heat. Since the night sky, especially on a clear night, is a giant reservoir for radiant heat transfer, our system cools the concrete, and hence the space, even with a very low difference between interior and exterior air temperatures. The result is cooling without using compressors or refrigerants - essentially passive cooling.
A second major innovation is the use of geopolymers to produce a different class of concrete binder that contains no Portland cement. Portland cement, the conventional binding material in concrete, is responsible for 5-8% of our collective worldwide carbon footprint. The geopolymer mix we are using completely replaces the Portland cement with a UNC Charlotte developed fly-ash mixture that results in a massive decrease in associated carbon emissions (theoretically up to a 90% reduction) and makes safe use of a waste product of coal production. Though there are some differences in the production cycle (the concrete has to be heated to cure for example), the precast panels for UrbanEden have been produced in partnership with a commercial pre-cast provider in a plant typically used for Portland cement mixes, suggesting that geopolymer mixes could offer essentially plug-and-play replacements for Portland cement.
UrbanEden will be reassembled on the campus of UNC Charlotte in conjunction with the opening in August 2014 of a new Charlotte-Mecklenburg Schools early college high school which will focus on science, technology, engineering, and math (STEM). The house will be used as an educational and research facility serving both high school and college students. Stayed tuned to the website and the UrbanEden Facebook page for updates.