DARMSTADT, Germany — From the outside, there is nothing unusual about the stylish new gray and orange row houses in the Kranichstein District, with wreaths on the doors and Christmas lights twinkling through a freezing drizzle. But these houses are part of a revolution in building design: There are no drafts, no cold tile floors, no snuggling under blankets until the furnace kicks in. There is, in fact, no furnace.
The Energy Challenge
Articles in this series are examining the ways in which the world is, and is not, moving toward a more energy efficient, environmentally benign future.
In Berthold Kaufmann’s home, there is, to be fair, one radiator for emergency backup in the living room — but it is not in use. Even on the coldest nights in central Germany, Mr. Kaufmann’s new “passive house” and others of this design get all the heat and hot water they need from the amount of energy that would be needed to run a hair dryer.
“You don’t think about temperature — the house just adjusts,” said Mr. Kaufmann, watching his 2-year-old daughter, dressed in a T-shirt, tuck into her sausage in the spacious living room, whose glass doors open to a patio. His new home uses about one-twentieth the heating energy of his parents’ home of roughly the same size, he said.
Architects in many countries, in attempts to meet new energy efficiency standards like the Leadership in Energy and Environmental Design standard in the United States, are designing homes with better insulation and high-efficiency appliances, as well as tapping into alternative sources of power, like solar panels and wind turbines.
The concept of the passive house, pioneered in this city of 140,000 outside Frankfurt, approaches the challenge from a different angle. Using ultrathick insulation and complex doors and windows, the architect engineers a home encased in an airtight shell, so that barely any heat escapes and barely any cold seeps in. That means a passive house can be warmed not only by the sun, but also by the heat from appliances and even from occupants’ bodies.
And in Germany, passive houses cost only about 5 to 7 percent more to build than conventional houses.
Decades ago, attempts at creating sealed solar-heated homes failed, because of stagnant air and mold. But new passive houses use an ingenious central ventilation system. The warm air going out passes side by side with clean, cold air coming in, exchanging heat with 90 percent efficiency.
“The myth before was that to be warm you had to have heating. Our goal is to create a warm house without energy demand,” said Wolfgang Hasper, an engineer at the Passivhaus Institut in Darmstadt. “This is not about wearing thick pullovers, turning the thermostat down and putting up with drafts. It’s about being comfortable with less energy input, and we do this by recycling heating.”
There are now an estimated 15,000 passive houses around the world, the vast majority built in the past few years in German-speaking countries or Scandinavia.
The first passive home was built here in 1991 by Wolfgang Feist, a local physicist, but diffusion of the idea was slowed by language. The courses and literature were mostly in German, and even now the components are mass-produced only in this part of the world.
The industry is thriving in Germany, however — for example, schools in Frankfurt are built with the technique.
The United States Army, long a presence in this part of Germany, is considering passive-house barracks.
“Awareness is skyrocketing; it’s hard for us to keep up with requests,” Mr. Hasper said.
Nabih Tahan, a California architect who worked in Austria for 11 years, is completing one of the first passive houses in the United States for his family in Berkeley. He heads a group of 70 Bay Area architects and engineers working to encourage wider acceptance of the standards. “This is a recipe for energy that makes sense to people,” Mr. Tahan said. “Why not reuse this heat you get for free?”
Ironically, however, when California inspectors were examining the Berkeley home to determine whether it met “green” building codes (it did), he could not get credit for the heat exchanger, a device that is still uncommon in the United States. “When you think about passive-house standards, you start looking at buildings in a different way,” he said.