How residential buildings can stay cool in the future

The heat is already hammering homes – and it will get even hotter in the next few years. How do we manage to keep living spaces cool enough?

She could not have put it more drastically: Renate Hammer spoke of “life-threatening situations” that the threat of global warming will soon bring us in the cities. “No one will be able to stay outside in summer,” said the managing partner of Building Research & Innovation a few weeks ago at the association’s conference.

Airing out at night in Vienna is no longer much use

The talk was about the so-called RCP 8.5 scenario: the rise in outdoor temperature that we are threatened with if not enough is done to combat climate change, but instead everything remains grosso modo as it is (“business-as-usual scenario”). Then neither the east nor the west of the country will be “liveable” in a heat wave, because then it will be over 45 degrees for several days in the dense city; in Innsbruck, where it is already warmer on average than in Vienna, it will be even worse than in the federal capital.

At the same time, anything above 35 degrees already means a “strong thermophysiological stress”, said Hammer. In Vienna, it will probably be so hot in summer in 2050 that it will no longer be possible to ventilate sufficiently at night. Recreation is only possible up to 23 degrees, “but then we will often have 24 to 26 degrees at night,” Hammer explains. And that can no longer be prevented. Interestingly, there is a relevant difference between Vienna and Innsbruck. Hammer compared the two cities in her lecture. Innsbruck is already warmer than Vienna during the day. “In the narrow valley location, the heat catches”; thus, by 2080 at the latest, “many places will no longer be liveable” in the Tyrolean capital during a heat wave at 3 p.m., the hottest period of a day. At temperatures above 40 degrees “you can’t do tourism any more, nobody can stay outside, the children can’t play, the old people can’t shop. It’s a life-threatening situation.” At night, however, it will continue to cool down so much in Innsbruck that it will still be possible to ventilate.

Air conditioning beats sun protection

And yet: If the RCP 8.5 scenario occurs, “we will soon have to cool all the buildings,” says Lutz Dorsch. He is head of the Climate, Environment, Buildings department at the Salzburg University of Applied Sciences and heads the “Cool Buildings” research project, in which the Danube University Krems is also involved. The best way to counter the impending heat waves is with passive cooling, he says. “But there is no one solution,” he hastens to add.

On the one hand, sun protection is, of course, excellent for keeping the heat out of the house in the first place. On the other hand, this is – at least at the moment – only necessary for a few weeks in summer, which is why property developers often still try to save on these costs. Air conditioning, on the other hand, is quite common in new buildings, at least in the upmarket segment. In Dorsch’s experience, it is precisely these systems that often ensure that existing sun protection is not even lowered during the day. “You switch on the cooling in the evening anyway, so why shade during the day?” But of course this is an energy-guzzling variant: first the heat comes into the house, then you need a lot of energy to get it out again.

Keeping energy consumption low

In fact, the goal is to create as little energy demand as possible “so that we can create what we need with renewables”. Dorsch is convinced that there will not be an oversupply of solar power in the future; “we want to charge all our cars with it soon. Electricity, namely for a circulating pump, is also needed if, for example, cooling is used via component activation. In principle, this is also a good idea, but it is not yet as widespread in the west of Austria as it is in the east, says Dorsch. “In itself, of course, this is also a form of active cooling,” especially when heat is introduced into the ground in summer so that it can be extracted again in winter.

Daylight is important

But how hot can it actually get in a living space, and how long can a person be exposed to it? According to Dorsch’s observation, these questions of health protection are treated stepmotherly. “We lack target values there.” These questions need to be discussed together with medical professionals, but that is completely lacking at the moment, Dorsch tells the STANDARD. And just as important is the question of how much daylight humans need.

Johann Gerstmann, spokesman for the Federal Association of Sun Protection Technology, also finds that this topic is not given much importance in comparison with fire, sound and noise protection measures. Yet it became very important in the pandemic with the much-practised home office: in summer, the blinds are down to keep the heat out. But because it is often too dark in the room, the light is turned up, which eats up energy. At the same time, at least 15 percent of the sun’s energy could or should enter the building, says Gerstmann. And he therefore recommends never closing the sun protection completely during the day. The best way to do this is with so-called markisolettes, i.e. folding awnings that provide shade at the top but let daylight in at the bottom.

Cold rooms in residential buildings

In order to be able to keep to the maximum, sun protection is indispensable for Renate Hammer. “We also have to do ambitious thermal refurbishment, which makes sense in winter as well as in summer.” And high-temperature processes, such as gas firing, have to be taken out of the houses. As for façade greening, there is no real clarity yet on its effectiveness in terms of cooling buildings, he said. “There is still a lot of research to be done there.”

Source: Standard.at, 23.06.2022

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