Once it's finished, a solar house being designed and built by Carnegie Mellon University students should be as comfortable as an old pair of Levis.
Its walls are made of denim. More precisely, the frame walls and roof panels will be filled with denim fiber -- almost 2,700 cubic feet of it -- that has been processed from the scraps of a Levi Strauss blue jean factory. The cotton fiber is both a natural insulator and naturally flame resistant and, packed inside 10-inch-thick walls, will achieve an insulating factor of R-50 that is two or three times times greater than that of a typical house wall.
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Wearing shorts and a hard hat, architecture student Andrew Lee supervises as a crane moves another piece into place last week on Resolution, the CMU team's entry into the Solar Decathlon competition. (Franka Bruns, Post-Gazette)
Related links
 Solar Decathlon Web site
Carnegie Mellon team site
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Using recycled cotton as insulation is just one way the team of 21 architecture, design and mechanical engineering students seeks to make the house energy efficient while conserving other natural resources.
The house is Carnegie Mellon's entry in the inaugural Solar Decathlon, a U.S. Department of Energy contest that culminates next month on the National Mall in Washington, D.C.
And the blue jeans filling the walls may in a way symbolize the school's goal of making the solar house comfortable as well as energy efficient. The aim of the decathlon is to demonstrate not only that solar technologies are maturing, but that living in a "zero-energy" house need not be what Vice President Dick Cheney would describe as "a sign of personal virtue."
"They're trying to show the public that renewable energy is here, that's it's close to affordable and that it doesn't require you to sacrifice your lifestyle," said Stephen Lee, an architecture professor and advisor to the CMU team.
The Solar Decathlon is the latest brainchild of Richard King, who heads photovoltaic research and development for DOE and who earlier dreamed up the Sunrayce, a biennial contest of solar-powered cars designed by engineering students. For the Decathlon, 14 teams of university students -- selected last year from a larger pool of contest proposals -- are designing and building 500- to 800-square-foot houses that depend completely on solar energy.
Each team will transport the houses to Washington and set them up on the Mall for the competition, scheduled Sept. 27-Oct. 4. Each structure must capture enough solar power to supply its own energy needs, including a computer-equipped home office, and to charge an electrically powered Ford Th!nk, a glorified golf cart that the students will use to run errands.
Each entry will be judged in 10 categories, including livability, hot water, refrigeration, lighting and "getting around."
The intent is to push existing technology to its fullest and perhaps come up with some innovations. But in contrast to the Sunrayce, which involves vehicles unlike anything else on the road, the solar houses could be immediately relevant, said Cecile Warner, Decathlon project manager at the National Renewable Energy Laboratory in Golden, Colo.
"I don't think most people imagine that they'll have a solar-powered car in their lifetime, but there are lots of people who imagine they might live in a solar-powered home," added Warner, a photovoltaics researcher.
A summer's worth of work
The Carnegie Mellon entry, dubbed "Resolution," is now rising on campus in the green area known as Donner Ditch, where the students have been hammering and sawing five days a week since mid-June.
Each team received $5,000 from DOE to begin its house. The actual cost of the CMU house will be about $150,000, with additional donations obtained through the help of Susan Tolmer, assistant director of development for the College of Fine Arts.
Unlike the other entries, which are all ranch-style houses, Resolution is designed with a loft bedroom so it will better fit on a city lot. "They're the only ones approaching this from the perspective of an urban townhouse," said the DOE's King. "I find that refreshing and nice."
Andrew Lee, a fifth-year architecture student (and no relation to Stephen Lee) who is serving as Resolution's chief architect, said the team felt so strongly that solar homes must be compatible with city living that they decided to build the loft even though they will exceed the contest's 18-foot height limit.
They'll lose a few points in the judging, he acknowledged, but that will be better than blindly accepting the rules. "You really can't have houses that sprawl out," he added.
In addition to the extra-thick walls, the windows are triple-paned to increase their insulation rating. A heat-recovery ventilator will allow fresh air to enter and stale air to exit the house, while recapturing the heat from exhaust air during heating season and precooling the fresh air during cooling season.
The roof will support 42 photovoltaic panels, which convert sunlight directly to electrical current, producing a total of 7 kilowatts. Unlike a standard home installation, where electrical grid connections allow excess power to be sold to electric utilities when the sun is shining and supplemental power to be purchased when the sun isn't shining, the contest homes will store power in batteries for night use.
To produce hot water, water will circulate through tubing attached to two-inch-wide metal solar heat collectors encased in 120 glass vacuum tubes, each almost 6 feet long. The vacuum in the glass tubes insulates the heat collectors, preventing loss of the solar energy back to the atmosphere.
A flat portion of the roof not occupied by solar collectors will be a "green roof," with earth and plant materials to provide a visual amenity and to dissipate summer heat.
The house will be heated and cooled using an electric heat pump. Normally, a ground-source heat pump uses a 150-foot-deep well; the earth at that depth is about 52 to 55 degrees year-round and can be a source of heat when temperatures dip below that and a means for cooling during the summer.
The National Park Service, however, won't allow drilling on the National Mall, Stephen Lee said. So the team will use a large water tank that will be linked to both the heat pump and the solar hot water system. In this solar-assisted heat pump, the hot water system will help the heat pump warm the house in winter, while heat removed from the house in summer can be used to produce hot water.
"If it works," Stephen Lee said, "it will revolutionize heat pumps," eliminating the $5,000 to $8,000 cost of drilling a well for a heat pump.
The students were excited about using a composting toilet, but that would have required digging a six-foot hole, another no-no for the park service. None of the entries will have working toilets on the mall.
The raised, bamboo plywood floor will be built with interchangeable tiles. Some of the tiles will include electrical and computer connections that can be moved anywhere they are needed. Rather than traditional plumbing, with water service lines snaking off from each other, the house will employ a manifold system, with each faucet served by its own flexible water line connected to a central manifold. The manifold is better able to stabilize pressure, Stephen Lee said, minimizing the risk of a shower losing pressure when somebody flushes a toilet.
With the exception of a kitchen-bathroom-laundry room module, sized to fit underneath bridges and in highway tunnels when transported to Washington, the house is built in four-foot-wide, eight-foot-high sections for easy assembly, disassembly and transportation.
The construction pace has lagged, however; the team didn't expect to finish enclosing the house until today. By contrast, the University of Puerto Rico finished its house and this weekend began shipping its pieces to Washington. The University of Virginia entry is being tested, King said, and Virginia Tech has already built its house and has tested disassembling it.
Consequently, Stephen Lee said, the CMU team won't have as much time to test the house as they would like. So, once the competition is over, the team is tentatively planning to bring the house back to campus, re-erect it on a permanent foundation, and have students live in it for a year or two to see how it works.
Eventually, they hope to add another story to the house and place it in a neighborhood such as East Liberty or Garfield for permanent occupancy.
Whether solar houses are the answer to sustainable housing is not yet known, said Andrew Lee, but the team members have been excited that the Solar Decathlon at least is addressing some issues that are growing in importance.
"At some point," he explained, "society is going to wake up and say, 'We're out of land and we're out of energy.'"
Byron Spice can be reached at bspice@post-gazette.com or 412-263-1578.
