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At first glance, the view could be confused with Hobbiton's rolling hummocks, up to perfectly circular gates opening onto a lush green hill. But the doors are glass and, inside, are not comfortable hobbit holes, but a set of heavy arms and mechanical steel levers retaining some of the half-open doors.
These hills are part of the roof of the California Academy of Sciences in San Francisco, United States. The green corrugated roof is part of a series of technical and conceptual features that make the academy one of the largest passive ventilation spaces in the country. This means that even at the height of summer, most of this building relies on cleverly handling the elements to stay cool without air conditioning.
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Architects, engineers and designers are rethinking buildings this way to find ways to keep them cool without air conditioning. The challenge becomes more and more urgent. The year that has just passed has been marked by the heat waves that swept through Australia, Southeast Asia, North America and the United States. Europe. To cope with heat waves, made more frequent by climate change, the number of air conditioning units is expected to more than triple in the world by 2050. Huge amounts of electricity, air conditioning units contain refrigerants that are powerful greenhouse gases. These refrigerants are in fact the fastest growing source of greenhouse gas emissions in any country in the world.
But there are alternatives and many of them. From 7,000-year-old building designs to state-of-the-art California Academy of Science technology, it's possible to create buildings that stay cool with virtually no energy demand.
At the academy, the grassy domes of the roof deflect the flow of natural air into the building. When the wind blows, one side of the hill is subjected to negative pressure, which helps to draw air through the automatically controlled roof windows and into the building. The fact that the roof is covered with vegetation also helps to reduce the temperature in the space below, while providing habitat for wildlife above.
What about much more ordinary everyday buildings in which most of us spend the majority of our time?
"We start by asking ourselves where we can go in designing the building on the premise that we will not have air conditioning," says Alisdair McGregor, world leader in mechanical engineering at Arup, who participated to the design of the building. . But it is rare to completely control the climate of the entire building by this approach, he adds. There may be constraints imposed by a noisy highway next to a building, making it impossible to open windows. Or, the building could have a lot of hot equipment or people with special needs, like in a hospital. But at least that means that the CA, as well as its costs and emissions, are kept to a minimum.
The California Academy of Sciences is a peak in passive design. But it was also a project worth nearly half a billion dollars to which the best engineers and architects of sustainable development have access. What about the much more ordinary everyday buildings in which most of us spend the most of our time – can passive cooling also make them heat-resistant?
L & # 39; water
One of the simplest forms of passive cooling uses the change in air temperature when the water evaporates. Water needs energy to move from the liquid state to the steam and the energy of the air as heat.
"Evaporative cooling is a natural phenomenon," says Ana Tejero González, an engineer at the University of Valladolid, in northern Spain. "We can see many examples in nature where this happens." It can cool a surface as well as an air body, such as your skin when you sweat, or the tongue of a dog when it kills.
In the Spanish region of González, a traditional boat called botijo uses the same principle. Botijo is a large, porous clay pot that is used to carry water or wine, which farm workers took to the fields. Small amounts of drink evaporate through the pores of the clay walls, keeping the liquid inside even under the hot Spanish sun.
In architecture, the use of evaporative cooling dates back to ancient Egypt and the Romans. But some of the most elaborate examples come from Arab architecture and a structure called mashrabiya. A mashrabiya is a network adorned with traditionally carved wood with intricate patterns, which are found on the outside or inside of a building. In addition to providing shade, the mashrabiya sheltered in summer porous earthen pots – like the botijo - filled with water. These would help cool the room while a breeze was crossing the mashrabiya and the pots.
Even in hot, dry, exposed climates, the coolest temperatures are never far away
But there are even simpler ways to control evaporative cooling in a building or outdoor space. A water plan in a yard – a pond, a fountain or runoff channels – does the same job. And indoors, placing a pot of terra-cotta water near a window or asphalt can help cool things down.
Earth
If the currently temperate northern regions of the world are going to be equipped to cope with the current extreme heat, there is much to learn from the old and modern buildings in the south of the world, says Manit Rastogi, founding partner of architecture firm. Morphogenesis company, based in India. "This part of the world has always been hot," says Rastogi. Passive cooling systems have been a necessity for thousands of years. "Most architectures that we have traditionally built here are phenomenal examples of obtaining cool conditions without mechanical means."
Even in hot, dry, exposed climates, the coolest temperatures are never far away. In Jaipur, the capital of Rajasthan State, in northern India, daytime temperatures regularly reach 40 ° C in summer. But a few meters below ground, the temperature of the earth in the region remains much softer, even in the most violent summer heat.
The solution is to dig, says Rastogi, who designed the Pearl Academy of Fashion in Jaipur according to this principle. Rastogi and his colleagues used a traditional Indian stepwell or baoli in a shady courtyard courtyard of the academy. Steps of gray stone steps descend transparently to the edge of a large pool of collected rainwater and treated wastewater from the building. The pool, cooled by underground temperatures, absorbs a substantial amount of heat from the yard and keeps the air fresh. "Digging in the ground is very, very effective," says Rastogi.
Although this is an attractive solution, it is not necessary to dig a huge well inside your property to use the same phenomenon. Commercial floor heating and cooling systems also use the more or less stable temperature of the planet throughout the year by pumping liquid into pipes buried outdoors. The temperature of the liquid reaches that of the earth and is then pumped inside, where it can pass through pipes under the floor to cool the house. These systems can be used both to heat buildings in winter and to cool them in the summer. Their overall use for heating has been slow, but they are becoming more popular for cooling, especially in the northern cities of China in the summer.
Many of these strategies involve staying in touch with nature and understanding how it works – Manit Rastogi
In addition to its basics, the Pearl Academy of Fashion in Jaipur uses a few other tips to control the temperature. From the outside, the building has a simple rectangular shape, which may not seem very elegant, but has the advantage of maximizing the interior space for the outer surface, each square foot exposed to the absorbing sun heat. The building is surrounded by a jaali, or perforated stone skin, located about four feet from the outer walls, which helps to shade the building and dampen the temperature. "Many of these strategies involve staying in touch with nature and understanding how it works," says Rastogi. "Understand the site and this particular typology, and the work will be much easier."
The result is that the interior of the academy is relatively lukewarm, even during the hottest months, when outside temperatures regularly exceed 40 ° C. This allows the air conditioning to be used very modestly, where appropriate.
Wind
The city of Yazd, Iran, is known as the "attractive city". Windcatchers are towers with arched windows without glass placed on top of flat-roofed buildings, facing the direction of the prevailing winds. For centuries, these towers caught the breeze and directed it toward homes, divided into canals by a series of blades inside the tower. The curved roof of the blower helps to promote air circulation, even in the absence of strong breezes. Sometimes the air flows over a basin of water, or even a deep tank in a dome-shaped chamber, to promote cooling.
According to the study of Mahnaz Mahmoudi Zarandi, an assistant professor of architecture at the Azad Qazvin Islamic University in Tehran, Yazd's wind turbines are among the most varied and creative in the Middle East. An analysis of the Yazd wind sensors revealed that the most efficient models lowered the temperature of the air within 40 ° C to 29.3 ° C.
According to Arup's McGregor, there are still options in ordinary buildings that are not fortunate enough to have an integrated windbreak. Having windows open on different sides of a building at different heights can help suck the air. "You sometimes see that effect too much and you almost make a screaming gust of wind," McGregor said. "For example, a large atrium with an opening at the top and a door at the bottom. But by changing the openings, you can control the flow of air through the building. "
Concrete jungle
Thinking about the scale of individual buildings, as ingenious as it may be, can only bring down the thermostat up to now. But understanding how buildings interact with the rest of the urban landscape can help reduce it further.
Even without the tall loupes of skyscrapers that burn the sidewalks, there remains the problem of the urban heat island effect
The London skyscraper, known as "walkie-talkie", offers a lesson on how not to do it. The building has a giant concave face. Although it may sound sophisticated, there is a reason that curved skyscrapers are not very common. Before the end of the work, it was discovered that the large, concave, bright surface acted as a magnifying glass, focusing the sun's rays on a small area. It was a few feet from the sidewalk in front of a Vietnamese hair salon and restaurant. The result was so hot temperatures that the paint had melted, blistered and distorted car parts, broken tiles and a burnt down mat.
The problem is now solved with the addition of a last minute sun breeze, or giant sunshade in aluminum slats. But it shows how much a design change can change the temperature of the cityscape. Even without the size of a skyscraper burning on sidewalks, there is the problem of the urban heat island: a dull, gray concrete absorbs the heat of the sun and sends it back to deafening pedestrians, like a bottle of water. hot water superfluous.
We could think of the heat island effect as a necessary evil of summer in the city. But urban spaces can be adapted to reduce it. One of the most effective ways is to bring in vegetation. We all know it intuitively – it's the difference between the shaded, tree-lined boulevards of a city like Palma, Mallorca, and the sidewalks exposed to the New York burn.
In Medellín, Colombia, city authorities have experimented with "green corridors" across the city. They built 30 green corridors in otherwise gray parts of the city, using 18 roads and 12 waterways. These green bands lowered temperatures by 2 ° C. A study by Monica Turner, an ecologist at the University of Wisconsin-Madison, showed that an even more extensive tree cover can reduce urban temperatures by up to 10%. At 5 ° C.
Even in a building that is passively cooled in a well-designed city, these design measures are sometimes not enough.
Many cities take similar measures. Milan's municipal authorities plan to plant three million trees in the city by 2030. Melbourne, Australia, has also launched a tree-planting program to keep the city liveable with future heat waves. And new cities, such as the forest city of Liuzhou in China, are able to weave vegetation cover from the beginning.
Exit strategy
Of course, even in a passively cooled building in a well-designed city, these design measures are sometimes not enough. In a hospital with equipment that generates heat and vulnerable people, the cooling requirements go beyond what passive systems can achieve. "Here we do not care much about energy, we just need to get the right thermal conditions inside," says Tejero González from the University of Valladolid.
But the end result is that conventional air conditioning should be a last resort, not a crutch. The most promising thing about passive cooling, says McGregor, is that it helps to break the vicious circle in which we are currently stuck with air conditioning: using technology that keeps the cold and helps warm the world. .
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