By Ursula Sautter, Ode magazine
How can a new kind of home drastically reduce fuel bills, CO2 emissions, and produce more energy than it consumes? Rolf Disch, an architect and environmentalist in Freiburg, Germany, has been asking this question and seeking out answers.
“What if each house became a power plant, if it created even more energy than it used internally?” Disch, 65, first asked himself 15 years ago. To design that home, he built on the ideas of the “passive house” movement that started in Europe in the early 1990s. Instead of relying on the electricity grid for power, a passive house taps available energy sources–sunlight, the body heat of occupants, even the thermal gains created by ordinary domestic activities such as cooking, bathing and using electrical appliances. The building is well-insulated and airtight so it retains most of this energy and, through highly efficient heat-exchange ventilation technology, uses it to cool itself in summer and heat itself in winter. The houses are called “passive” because most of the power consumed is collected from ambient energy in the environment. When extra juice is needed, renewable power units supply it, like the solar array on the roof of the residential and commercial complex Disch built in Freiburg in 2004.
“I only ever had to switch on the heating once,” says Stefan Sattler, a 32-year-old lawyer who has rented a penthouse in the Disch-designed complex since October of 2007. Even then, Sattler only needed the extra heat–purchased from the local heating grid–for two or three hours. Since he and his fellow residents sell the surplus energy produced by the building’s solar panels back to the city’s utility provider at a profit, Sattler is one of the few people who opens his utility bills with real glee. He’s earning money from solar power rather than paying for oil or gas. The average unit in the Freiburg complex earns $5,075 a year this way instead of spending $4,625.
Passive homes can save consumers a bundle in fuel bills–and the planet even more in CO2 emissions. According to the German Passive House Institute (PHI), founded by physicist Wolfgang Feist, who co-created the passive house concept, energy consumption can be reduced by up to 90 percent compared to average homes, up to 75 percent compared to newer buildings. While an existing home uses some 160 kilowatt-hours in heating energy per square meter of living space (kwH/m2) annually, residences built to the passive house standard use a maximum 15 kwH/m2.
Insulation is crucial to making these houses work. The walls in Disch’s complex, which comprises a 50-unit housing estate as well as a five-story commercial center (with Sattler’s penthouse on top), have “extra-thick insulating layers and are almost free of ‘thermal bridges,’” he says, referring to poorly insulated areas where heat gets lost. “The windows have infra-red-reflecting, vacuum-sealed triple glazing that allows lots of solar rays to enter but like the walls, prevents the resulting warmth from escaping again.” Each roof has an awning constructed at such an angle that it shields the interior from the high summer sun but lets the low winter sun permeate the dwelling. The panels on the roof generate electricity. All this, says Disch, “enables the structure to produce energy, use it intelligently, and retain it.” Five other German towns and cities are planning similar complexes.
Some worry that living in one of these novel houses might be too much like living in a thermos. Yes, your fuel bills are lower, but what if you felt like leaving the front door open on a summer evening? According to Sattler, that’s not a problem: “There is a popular prejudice that these houses have to be kept tightly shut so that no energy is lost, but that’s not true. You can open the windows like in any normal building.”
Even with the doors and windows closed, the heat-exchange ventilation systems creates a pleasant, healthy indoor climate. Temperatures typically hover around 72 degrees Fahrenheit (22 degrees Celsius), whether it’s a December morning or a July afternoon. A 2005 report by the Austrian Ecology Institute found that the “more effective air exchange” in passive houses meant the concentration of pollutants “was markedly lower than in houses without ventilation systems where the same construction materials had been used.” The study also found that levels of dust, pollen, microbes and radon–an odorless, colorless gas associated with lung cancer–were all lower than in ordinary buildings.