Solar Decathlon 2011: A Refined Design from Ohio State
The performance of this efficient house depends not just on solar technology, but on strategic shading and a superinsulated airtight envelope
As it prepares for its second Solar Decathlon, the team representing Ohio State University is building a house whose design emphasizes passive features — a superinsulated, airtight shell and triple-glazed windows — and then brings the building’s operation to net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. with a photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array and a solar hot water system.
The name of the project — enCORE — is a reflection of the design approach, as well as the fact that Ohio State competed a previous Solar Decathlon competition in 2009.
The central core of the house is where its mechanical and plumbing systems reside, and that core anchors the rest of the flexible layout layered around it. Storage space, the bathroom, and the kitchen are clustered close to the mechanical room, with a den and open living room configured at one end of the layout and two bedrooms at the other. The enCORE team condensed the mechanical and storage areas as much as was practical to make the 1,000-sq.-ft. home, which is designed to accommodate a family of three, feel spacious and comfortable.
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Steve Winter, the team’s architecture advisor, told Fine Homebuilding that while the house will produce its own electricity and heat its water via solar technology, the building’s energy efficiency derives mainly from its superinsulation, airtightness, and other passive features such as solar orientation, shading, and cross-ventilation.
A strategy for portability
Shading is provided by enCORE’s final, outer layer: a system of adjustable, diaphanous screens that shield the exterior walls (and make the building appear bigger) while they enhance the building’s overall performance and appearance. “The exterior of the house itself is supposed to feel really light, transparent in places, so you can get these notions of how the house is formed beneath the exterior façade,” Winter said.
Grouping the mechanical systems in the center of the house, he added, allowed the team to not only house the hardware and pipes compactly but also assemble and dissemble the house more easily.
“The logistical complexity of this project, and the fact that we have to take them apart and ship them” made a compelling argument for locating the mechanical room where it is, he said. “When you build these houses on a permanent site, it’s nice to have a central core as well, but it really helps us in transporting the project.”
The thermal resistance of enCORE’s floor is designed to be R-55; the exterior walls, R-41; and the roof, R-65. Matthew O’Kelly, an enCORE project engineer, told GBAGreenBuildingAdvisor.com that the team is aiming for close to PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. performance with off-the-shelf insulation products and American-made windows, and that construction costs are expected to be slightly less than or equal to $300,000.
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O’Kelly pointed out that, in keeping with Solar Decathlon rules, all contest entries, including enCORE, are ADA-compliant. He also noted that, like many other Decathlon entries, enCORE features a flat roof (and a separate structure for photovoltaic panels) that plays into the building’s contemporary design aesthetic and makes shipping the house easier, especially given the 12-to-13-ft. bridge clearances encountered on many routes to Washington.
The range of contest requirements and team-member responsibilities, O’Kelly added, makes Decathlon participation an exceptionally rich learning experience. “HVAC and building science are not necessarily subjects that are widely taught anymore,” he wrote in a recent email. “If not for this project I don't know that I would have been exposed to either of these disciplines. Experience is valuable, and eventually we will need a new generation of engineers to take on these challenges. Solar Decathlon (realistic in nature or not) prepares engineers and architects to solve these problems in a multidisciplinary, hands-on environment. That alone makes this project worthwhile.”
The current post-Decathlon plan for enCORE is to ship it to Columbus, Ohio, where land formerly used for industrial purposes is being repurposed for residential communities and common spaces. If a suitable site can be found, the house will fulfill its intended end-user role as a home for a couple or family of three.
For an overview of the Solar Decathlon teams, see GBA's 2011 Solar Decathlon Resource Guide
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