Why do windows open inwards in Germany?

Long considered to be a key measure for good respiratory hygiene, Germans often crack open windows to let nasty, stale air out and fresh, but cold, air in, even in the dead of winter.

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Germans are obsessed with lüften, the act, or art, of ventilating their homes — but it is undermining efforts to make buildings more energy efficient. Long considered to be a key measure for good respiratory hygiene, Germans often crack open windows to let nasty, stale air out and fresh, but cold, air in, even in the dead of winter. But for all the enthusiasm for crisp air circulation, researchers suggest that the national devotion to lüften may be actively undermining buildings' energy efficiency — and Berlin's emissions reduction goals. Buildings are responsible for approximately 40 percent of the EU's energy consumption and 36 percent of the bloc's CO2 emissions. As part of its drive to achieve climate neutrality by 2050, Brussels is pushing to make member countries' building stock emissions-free. Initiatives like its Renovation Wave strategy aim to improve the quality of the roughly three-quarters of EU buildings that aren't energy efficient. Germany has tackled the issue through its wider Energiewende green energy scheme, which set the goal of slashing primary energy consumption in residential and non-residential buildings by 80 percent by 2050. It also introduced tougher rules in its energy savings directive, which regulates heating technology and thermal insulation. But despite those efforts, CO2 savings in the building sector since 2010 have been very moderate. One reason the impact may have been less than expected is that while Berlin's guidelines have resulted in buildings that are technically very well insulated, costly energy efficiency elements have been largely undercut by residents' lüften practices, according to an article in the journal Energy and Social Science. "The buildings we looked at were well insulated, but residents didn't fully understand the heating features, or the air recovery systems incorporated into the home," said Amelie Bauer, a researcher at Munich's Ludwig Maximilian University and one of the study's authors. "They stuck to their habits and kept opening windows to ventilate in accordance with their preferences." In the study, Bauer and her colleagues highlighted the different ventilation and temperature preferences of two residents of the same apartment building. One was a German woman who kept her windows open so that her living room was a brisk 19 degrees. The other was a Greek man, who preferred his home to be a balmy 27 degrees.

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"Those different preferences and habits place big demands on a single building when it is equipped with smart technology to keep air circulating and conserve heat, " Bauer said. "There's a tendency to create passive housing that is designed to be energy efficient without residents doing anything, but that ignores the fact that people are stubborn and do things anyway, and not in the standard way that's been recorded in engineers' labs."

Shock ventilation

An added problem is that German ventilation habits may themselves be very inefficient. "The correct way to ventilate a home is to employ the Stoßlüften, or shock ventilation method. You open your windows completely for three minutes if it's windy, five to 10 minutes if it's not," said Raymond Galvin, a researcher at the University of Aachen and Cambridge, who has written extensively about energy efficiency in Germany. "The problem is that, although most Germans swear that they only practice Stoßlüften, my research has found that hardly anyone actually does," he said, adding that the shock ventilation method was likely little used because of a fundamental design flaw in German homes. "In a country like Germany, windowsills are prime real estate for potted plants that need light, and framed pictures of your favorite grandmother," Galvin said. "But in Germany, the windows open inward, and nobody has time to clear that all out twice a day to fully open the window, so instead, people just open their window to a slightly tilted position." According to the researcher, it can take up to two hours to ventilate a room with windows that aren't fully open, and in that time, the walls cool fully, meaning more energy in needed to warm the room up again. Galvin conceded that it was unlikely Germany would change such a fundamental element of its housing design, but said it was a shame that a country that was "generally very good at moderately high-tech design is bad at basic stuff like noticing that there's a socio-technical mismatch between residents' needs and what windows are designed to do."

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The answer, Bauer said, might be to simply insulate less.

"The key may be to have less insulation, because the current system seems to be too airtight to accomodate for residents' differing preferences," she said. "There are around 90 million buildings in Germany and about half will need to be renovated in the next 20 years, so less intense and less costly renovations would let us make more of them energy efficient faster." She added that the government would do well to expand its focus beyond just energy efficiency and look into how Germans really live. "People are living in increasingly big homes, so even though the energy costs per square meter have declined, the gains we've made through energy efficiency have been eaten up by the increase in living space per capita," she said, adding that Berlin might be well-served by teaching people to "live better with less." This article is part of POLITICO’s premium policy service: Pro Energy and Climate. From climate change, emissions targets, alternative fuels and more, our specialized journalists keep you on top of the topics driving the Energy and Climate policy agenda. Email [email protected] for a complimentary trial.

politico.eu - Germany's inefficient love affair with open windows - POLITICO