A group of students from Rutgers, the State University of New York and the New Jersey Institute of Technology (NJIT) comprise what is known as Team New Jersey. Together they are one of twenty college teams competing in the 2011 Solar Decathlon, sponsored by the U.S. Department of Energy (DOE). The aim of the competition is to build the most cost-effective, energy-efficient and attractive house using optimal energy production. This year, Team New Jersey constructed the first precast concrete sandwich panel house, dubbed the ENJOY house, ever to be entered into the competition. By using precast concrete sandwich panels with less steel and more fiberglass products, the team wants to highlight the use of composites in their energy efficient, “passive” house design.
Unique to the Team New Jersey design, the passive strategy focuses on using basic architectural design techniques to reduce thermal transmissibility through insulative materials. “By strategically using fiberglass in the windows and reducing transmissibility in the frames, we actually ultimately do less work to keep a constant temperature in the house,” says Richard Garber, NJIT associate professor and Team New Jersey faculty leader. Concrete was chosen for its thermally efficient properties such as its ability to retain heat absorbed during the day and effectively release it at night. “We were trying to stay away from using steel because it expands and contracts differently than concrete, causing steel connectors to crack the concrete and transmute heat into the house,” says Garber. The concrete walls are framed with steel rebar to withstand the heavy weight of the concrete roof and solar panels instead of using an earlier proposal for an epoxy carbon fiber grid for reinforcement. However, some of the panels were intentionally designed with less steel to reduce thermal transmission, the window frames were designed with pultruded fiberglass and the team used fiberglass connectors from Hughes Brothers in Seward, Neb., in the wall, roof and floor panels.
The Anatomy of the Concrete Sandwich Panels
The design of the concrete sandwich panel for the Solar Decathlon house was developed by John Ruga, president of precast concrete manufacturer, Northeast Precast in Millville, N.J. In order to cast the walls, first the team set up the rebar in the formwork. Next, they poured a three-inch layer of precast concrete. Then they laid out six inches of polystyrene insulation mixed with Nuopor, a new insulation solution from BASF that includes graphite, and placed Aslan 700 fiberglass connectors on top. Another layer of rebar was then applied along with floor connections before another three-inch layer of concrete was poured into the formwork. So, as opposed to traditional precast concrete panels manufactured with concrete on the exterior and traditional mortar and wood on the interior, the groups’ panels use the fiberglass ties to assemble concrete panels on the interior and exterior of the house, increasing the properties of concrete and fiberglass to insulate the house.
By using different materials and basic design techniques, the house is much more energy efficient and capable of longer sustainability compared to that of traditional wood frame houses. Compared to similar one-story houses, these sandwich wall panels have an R-value, or a measure of thermal resistance, of 30.0 when traditional wood frame houses have an approximate R-value of 21.0.