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BBC – Future – Are there alternatives to air conditioning?

At first glance, the view can be confused with the rolling hummocks of Hobbiton, right down to the perfectly circular doors that open from the lush green hillside. But the doors are made of glass, and inside them are not cozy hobbies, but a number of large mechanical steel arms and levers that hold some of the doors in place.

These hills are part of the roof of the California Academy of Sciences in San Francisco, USA. The rolling green roof is one of a series of engineering and design features that make the academy one of the largest passively ventilated areas in the United States. This means that even at the peak of summer, most of this building relies on clever manipulation of the elements to stay cool, with almost no air conditioning.

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Ceilings like these are a way architects, engineers and designers re-evaluate buildings to find ways to keep them cool without air conditioning. The challenge is becoming increasingly urgent; It's been another fiery year, with heat waves rolling Australia, South Asia, North America and Europe. In order to cope with heat waves, which are more frequently caused by climate change, the number of AC units is expected to be more than tripled worldwide by 2050. In addition to venting huge amounts of electricity, AC units contain refrigerants that are strong greenhouse gases. Indeed, these refrigerants are the fastest growing source of greenhouse gas emissions in all countries of the world.

But there are alternatives, and many of them. From old building designs that have been tried and tested over 7,000 years, to the innovative technology of the California Academy of Sciences, it is possible to create buildings that stay cool with virtually no energy requirements at all.

At the academy, the roof's grassy domes divert the natural flow of air inside the building. When the wind blows over, one side of the hills is suppressed, which helps to suck air through the automatically controlled skylights and into the building. The fact that the roof is covered with vegetation also helps to bring the temperature down into the room below, as well as providing a wildlife habitat above.

What about the much more ordinary, everyday buildings that most of us spend most of our time in?

"We start with the attitude about how far we can go in designing the building on the assumption that we will not have AC power," said Alisdair McGregor, global manager of mechanical engineering at Arup, who was involved in the building's design. But it is rare to climate-control the entire building with that approach, he adds. There may be restrictions from a noisy freeway next to a building, making it impossible to open the windows. Or the building may have a lot of hot equipment or people with special needs, such as in a hospital. But at least it means that AC, along with the costs and emissions, is reduced to the bare minimum.

The California Academy of Sciences is a highlight of passive design. But it was also a nearly half billion project with access to some of the best engineers and architects in sustainable development. What about the much more common, everyday buildings that most of us spend most of our time in ̵

1; can passive cooling also make them heat-proof?


One of the simplest forms of passive cooling uses the temperature change in the air as the water evaporates. Water requires energy to go from liquid state to steam, and it takes the energy from the air in the form of heat.

"Evaporative cooling is a natural phenomenon," says Ana Tejero González, an engineer at Valladolid University in northern Spain. "We can see many examples in nature of this happening." It can cool a surface as well as a mass of air, such as your skin when you sweat, or a dog's tongue when it pants.

In the González region of Spain, a traditional vessel called a botijo ​​uses the same principle. Botijo ​​is a large pot made of porous clay and used to transport water or wine, which farm workers would take out in the fields. Small amounts of the drink evaporate through the pores of the clay walls, keeping the liquid inside cool even under the hot Spanish sun.

In architecture, the use of evaporative cooling goes back to ancient Egypt and the Romans. But some of the more elaborate examples are from Arabic architecture and a structure called mashrabiya. A mashrabiya is an ornate, traditional woodcarving carved with intricate designs, found on the outside or inside of a building. In addition to providing shade, mashrabiya would be the summer home to porous ceramic pots – like botijo ​​- filled with water. These would help cool the room while a wind broke through the mashrabiya and over the pots.

Even in exposed, hot and dry climates, cooler temperatures are never too far away

But there are even easier ways to utilize evaporative cooling in a building or outside the room. A body of water in a courtyard – a pond, fountain or stream that runs all over the place – does the same job. And inside, placing a clay pot of water near a window or a draughty place can help cool the place.


If temperate regions of the northern north will now be equipped to deal with routine extreme heat, there is much to be learned from buildings, both ancient and modern, in the global south, says Manit Rastogi, a founding partner of the architectural firm Morphogenesis, is based in India. "This part of the world has always been warm," says Rastogi. Passive cooling systems have been a matter of necessity for thousands of years. "Most of the architecture we've done traditionally here is phenomenal examples of achieving cool conditions without mechanical means."

Even in exposed, hot and dry climates, cooler temperatures are never too far away. In Jaipur, the capital of Rajasthan state of Northern India, daytime temperatures regularly reach above 40C in the summer months. But just a few meters below ground, the temperature of the earth in the region is still a much milder 25C, even through the most intense summer heat.

The solution is to dig down, says Rastogi, who designed the Pearl Academy of Fashion in Jaipur using this principle. Rastogi and colleagues used a traditional Indian step, or baoli, in an inner shaded courtyard at the academy. Tombstones banks seamlessly lead down to the edge of a large, still pool of collected rainwater and treated wastewater from the building. The pool, cooled by the underground temperatures, absorbs a significant amount of heat from the courtyard and keeps the air fresh. "Digging in the soil is very, very effective," says Rastogi.

While it may be an attractive solution, it is not necessary to dig a huge well inside your property to make use of the same phenomenon. Commercial ground heating and cooling systems also use the earth's more or less stable year-round temperature by pumping a liquid through buried pipes outside. The temperature of the liquid falls to the temperature of the soil and is then pumped in again, where it can run through floor pipes to cool the house. These systems can be used to both heat buildings in winter and to cool them in summer. The global uptake of them for heating has been slow, but they are becoming increasingly popular for cooling, especially in northern Chinese cities in the summer.

Many of these strategies are about being in touch with nature and understanding how it works – Manit Rastogi

Besides baoli, the Pearl Academy of Fashion in Jaipur uses a few other tricks to keep the temperature down. From the outside, the building is a simple rectangular shape, which may not look very elegant, but has the advantage of maximizing the amount of interior space for the outer surface, as each square foot exposed to the sun absorbs heat. The building is shrouded in a Jaali or perforated stone skin about four meters from the exterior walls, which helps to shade the building and buffer the temperature. "Many of these strategies are about being in touch with nature and understanding how it works," says Rastogi. "Understanding the site and the particular typology, and the job will be much easier."

The result is that the interior of the academy is a fairly warm 29C even in the hottest months, when the outside temperature regularly exceeds 40C. This makes it possible to use the air conditioner very modestly when it is needed at all.


The city of Yazd in Iran is known as a "banger city". The windscreens are towers with curved glass-free windows set on flat roof buildings, in the direction of the prevailing winds. For centuries, these towers have captured the breeze and channeled it down to the homes, divided into channels by a series of knives in the tower. The curved roof of the windscreen helps to encourage air circulation, even when the wind is not blowing. Sometimes the air flows over a pool of water, or even a deep reservoir in a dome chamber, to encourage further cooling.

The prisoners in Yazd are among the most diverse and creative in the Middle East, according to research from Mahnaz Mahmoudi Zarandi, assistant professor of architecture at Qazvin Islamic Azad University in Tehran. An analysis of Yazd's windscreens found that the most efficient models reduced indoor air temperature from 40C to 29.3C.

In ordinary buildings that are not lucky enough to have a windscreen built-in, there are still alternatives, says Arup & # 39; s McGregor. Having windows open on different sides of a building at different heights can help draw air through. "Sometimes you see that effect too much and you almost get a howling breeze through," McGregor says. “For example, a high atrium with an opening at the top and a door at the bottom. But by varying the openings, you can control the airflow through the building. ”

Concrete jungle

Thinking about the scale of individual buildings, no matter how cleverly designed, can only get the thermostat down so far. But understanding the way buildings interact with the rest of the urban landscape can help bring it a notch further.

Even without the magnifying glass magnifier burning the sidewalks, the question of the urban heat island effect

London's skyscraper, known as "walkie-talkie", provides a lesson in how not to do this. The building has a gigantic concave face. Although it may look fancy, there is a reason that curves inside are not very common. Before the building was finished, it was discovered that the huge shiny concave surface served as a magnifying glass, focusing the sun's rays on one small area. This focus happened to be a few feet of pavement outside a hairdresser and a Vietnamese restaurant. The result was temperatures so hot that paint melted, car parts blistered and cracked, tiles shattered and a doormat set on fire.

The problem is now solved thanks to the addition of a last-minute breeze solil, or huge sun visor made of aluminum slats. But it shows how profound a design adjustment can change the temperature of the urban landscape. Even without the magnifying glass size that reinforces the sidewalks, there is the question of the urban heat island effect – where dull, gray concrete absorbs the heat of the sun and radiates it out onto sweltering pedestrians, like a very unnecessary hot water bottle. [19659002] We can think of the heat island effect as a necessary evil in the summer in the city. But city space can be customized to reduce it. One of the most effective ways is to get some vegetation. We all know this intuitively – it's the difference between the shady tree-lined boulevards of a city like Palma, Mallorca and the windy exposed sidewalks of New York.

In Medellín, Colombia, city authorities have been experimenting with "green corridors" through the city, developing 30 green corridors in otherwise gray parts of the city, using the edges of 18 roads and 12 waterways, which lowered the temperatures by 2C A study by Monica Turner, an ecologist at the University of Wisconsin-Madison, showed that even wider woods can reduce urban temperatures by up to 5 C.

Even in a passively cooled building in a well-designed city, sometimes these designs measures will not be enough

Many cities are taking similar steps: 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 level through future heat waves. cities, such as China's Liuzhou Forest City, are able to weave vegetation cover from the start.

Departure Strategy

Of course, even in a passively cooled building in a well-designed city, sometimes these design measures won't be enough. In a hospital full of heat-generating equipment and vulnerable people, there will be cooling requirements that go beyond what passive systems can achieve. "Here, we don't care about energy so much – we just need to achieve the right thermal conditions indoors," says Tejero González, Valladolid University.

But the point is that conventional air conditioning should be a last resort, not a crutch. Perhaps most promising with passive cooling, McGregor adds, is that it provides a way out of the vicious cycle we're currently stuck with with air conditioning: to use a technology to keep cool that actually helps warm the world.

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