BERLIN — Worldwide researchers are experimenting increasingly with moss, algae and potted plants as a way to turn houses into multifunctional buildings. The question is "how a facade in a city neighborhood can generate additional value," says Steffen Braun of the Stuttgart Fraunhofer Institute's Urban System Engineering. Behind that lies "a whole new approach to engineering."
Buildings should clean the air, cool the surroundings, keep out noise, and capture energy. Here are 10 working ideas to help achieve that end.
1. Moss cleans the air
Like Braun, the Fraunhofer Institute's Holger Wack is among the researchers who believe that houses should offer an additional purpose. He wants to see large expanses of house walls covered with moss.
"Tests show how air behaves in high-rise street canyons and that it often comes into contact with facades," Wack says. "Moss-covered surfaces clean the air."
Because moss doesn't have roots, it has to get its nourishment from the air. It takes in pollutants too that integrate with the plant mass.
2. Color fights pollutants
To clean the air, scientists also use chemical substances — for example, nano titanium dioxide, which is found in food additives and is also mixed with paints to degrade air pollutants.
The material, which some researchers say is carcinogenic, already figures in the first commercially available coatings such as Eco Clean made by the French company Alcoa.
If the sun's ultraviolet rays hit a facade painted with a coating containing nano titanium dioxide, the chemical compound becomes a catalyst. It frees oxygen radicals, and they break up the nitrogen compounds in the contaminated air into water and nitrate. In this way the immediate surroundings of the building have markedly less industry and car exhaust than the rest of city air.
As the surface attracts moisture from the air, a thin film of water forms on the outside that makes pollutants slide off. Street pollution disappears too, thus keeping the facade clean. The coating also acts as ultraviolet protection so that it keeps rooms cool during the summer.
3. Roof gardens provide fresh air
Large green roof surfaces can also help with cooling and pollution.
Some 45 tons of fresh vegetables and fruit can be grown on 1,000 square meters of roof space, and the plants also help reduce carbon dioxide.
Rooftop farming could theoretically eliminate up to 10% of industry-generated carbon emissions from the air.
4. White roofs against climate change
Another idea for improving the climate is to use white tiles instead of red or dark ones for roofing.
By reflecting the sun's rays, they are supposed to slow down warming of the atmosphere close to the earth's surface. Whether the effect could really impact global warming is questionable, but the light-colored tiles would mean using less air conditioning, in turn decreasing carbon emissions.
5. Rainwater cools surroundings
Still-new technology helps to cool a home's environment, which is particularly important in cities where temperatures are often a few degrees higher than they are in the country.
To achieve this, small tubes are mounted in the outer wall. Through evaporation, the rainwater that flows through them reduces the temperatures of surrounding areas.
Facades covered with moss work in a similar way, says Wack.
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More moss, please. Photo: Liquen
6. Buildings protect from noise
Giving building facades more than one function was a development that started 40 years ago when houses began to be used as noise protectors. A well-known example is a Berlin housing complex for 4,000 people that stretches for a good 400 meters over a section of highway and protects the direct surroundings from traffic noise.
In the last couple of decades, the idea of using buildings for noise protection was put on the back burner as large living complexes lost attractiveness. But now we're seeing more and more of it to protect "higher value" properties from noise, says Andreas Timmermann of the Noise Protection Planning Bureau in Altenberge.
"In the inner city, such concepts will win out for space and cost reasons," says Timmermann.
The Hülpert Center is the first car park in Germany also conceived as a noise preventer. The building and other elements are meant to protect the houses behind it from too much traffic noise.
7. Algae facades produce biomasses
Houses can be retrofitted to provide at least enough energy for themselves. The Bio Intelligence Quotient House, which has been operational in Hamburg for a year, demonstrates how this can work.
It is the first building in the world with a bioreactor for a facade. On two sides of the building there are glass walls filled with micro-algae and water. The micro-algae produce usable warmth and biomass from the photosynthesis of sunlight.
Even more is possible with the algae house. Researchers want to use hydrothermal conversion to generate natural gas and hydrogen from the algae biomass. Fuel cells make it possible to gain electricity, heat, and the carbon dioxide the algae need. The result would be fully energy-independent houses.
Between the heat protection glass outside and the layer of algae, solar cells could also be incorporated. They would let the red light that algae need through and turn the energy into electricity.
8. Window panes deliver solar energy
Manufacturers can now integrate solar cells into window panes. Largely transparent modules are necessary for this to let in enough daylight.
Scientists at Michigan State University in East Lansing are now developing special foil that concentrates light coming through the panes on a solar cell. The foil contains organic salts that transform ultraviolet and infrared light into invisible light on another wavelength that the solar cells then transform into electricity.
Effectiveness is only around 1%, but up to 7% should eventually be possible.
9. Energy from scattered drops
Energy is being produced by a very special wind turbine developed by researchers at Delft University of Technology in the Netherlands.
The turbine is comprised of a frame on which numerous thin tubes have been mounted horizontally. Nozzles produce a continuous supply of positively charged drops of water.
If the wind blows, electrons in the frame produce electricity that feeds into the general power grid.
10. Wind turbines make use of drafts
The installation on the Bahrain World Trade Center is particularly spectacular as far as wind turbines mounted on buildings go. Three turbines 29 meters in diameter have been mounted between the building's two high-rise towers.
The towers are elliptical, which increases the speed of the coastal winds that pass between them.
The three turbines produce 225 kilowatt hours of energy and should cover about a third of the building complex's electricity needs.