Image Credit: Team Tidewater Virginia For its showcase at the Solar Decathlon competition, Unit 6 is designed as a free-standing single-family one-bedroom unit, but its function in the housing market will be as a component of a multifamily (six-unit) net-zero-energy complex slated for the Park Place neighborhood of Norfolk, Virginia. Unit 6’s exterior materials consist of exterior-grade plywood that functions as a rainscreen, battens, and trim. The main entry of the house opens into this sunspace, which features a large operable window that lowers to become flush with the railing that runs horizontally through the window assembly, converting the sunspace into an exterior space during the warmer months. A similar window system in the kitchen area also opens to the sunspace. Looking from the kitchen area into the living room. The north side of Unit 6. The utility core is enclosed in a pergola.
Team Tidewater Virginia set out to build a house that will work exceptionally well as a stand-alone home. The modular house is also designed to work as one of six units in a multifamily project being designed for the Park Place neighborhood of downtown Norfolk, Virginia. One key to bringing the project to life has been the team’s ability to see its multifamily project in Norfolk and its single-family Solar Decathlon entry as completely compatible, rather than divergent, enterprises. A collaboration of students and faculty at Old Dominion University and Hampton University, the team fittingly calls its Decathlon house Unit 6, and the team members seem almost as excited about eventually merging the house with the multifamily project as they are about showing off the building on the National Mall. Almost. At the Decathlon, though, Unit 6 will present as a 971-sq.-ft. one-bedroom home whose performance and amenities are being finely tuned to Washington’s fall climate and the expectations of the experts and regular folks touring the building. Its 2.64-kW photovoltaic array, for example, is designed to provide net-zero-energy performance on an annual basis in Norfolk, although it will accommodate seasonal conditions during the competition with an additional, 1.38-kW parallel array that will be installed on a flat-roof section of the building.
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The Unit 6 shell The house also is equipped with a 4′ x 10′ flat-plate solar thermal collector and 50-gallon hot water storage tank. When necessary, a separate in-line system kicks in to heat the water just before it reaches the fixtures. Mechanical equipment also includes a Mitsubishi Mr. Slim minisplit heat-pump system, with one outdoor unit and two concealed, ducted indoor units, with a total capacity of 22,000 Btu/hour. A variety of insulation strategies will bring the floor to R-35, the exterior walls to R-28, and the roof to slightly more than R-40. Project manager John Whitelaw points out that closed-cell spray polyurethane foam is being used to help seal the shell while providing thermal resistance of R-6 to the floor, R-14 to the walls, R-21 to most of the ceiling, and the full R-40 in the part of the sloped roof framed with 6-in. laminated-veneer beams. In addition to the 1 in. of spray foam used to seal and partially insulate the floor, high-performance EcoBatt will be installed to hit the R-30 value. On the exterior walls, batt insulation fills the rest of the 2×6 framing to bring that part of the enclosure to the R-28 level. The walls will be sheathed in paintable medium-density-overlay plywood. The pitched roof will be covered with thermoplastic polyolefin membrane and raised-seam sheet metal, while the flat roof, which is insulated inside with dense-packed cellulose and 1 in. of polyisocyanurate board outside the sheathing, will be covered with a white membrane to reflect sunlight.
MORE INFORMATION Team Tidewater Solar Decathlon Web page DOE Web page for Team Tidewater GBA Resource Guide for 2011 Solar Decathlon
Sealing and selling potential The team selected custom windows and exterior doors from Henselstone, based in Amissville, Virginia. Most of the windows will be triple-pane, although three on the south-facing wall will be double-pane units that offer a high solar heat-gain coefficient. While two large horizontal windows serving the building’s porch/sunspace area are motorized to open and close on a vertical track, the rest operate either as tilt/turn casement windows or tilt/turn hopper windows. In an e-mail about project details, Whitelaw says the team expects good results in blower-door tests. “Since our windows and doors are virtually airtight and the sheathing is all insulated with a coat of spray foam, our only major sources of unintended infiltration will be penetrations for the dryer vent, plumbing, and electrical wiring,” he writes, adding that results should be between 0.6 and 1.0 air changes per hour at 50 Pascal pressure difference. For transport, the building will break up into three modules, plus the roof assembly. Construction costs are expected to be competitive. The team estimates that an independent contractor could build the house for between $250,000 and $300,000, Whilelaw adds.