Five tricks to keep buildings cool without air conditioning

Brrrrr. Image: Matt Hinsta/Flickr/creative commons.

The warmer it gets, the more people crank up the air conditioning (AC). In fact, AC is booming in nations across the world: it’s predicted that around two thirds of the world’s households could have an air conditioner by 2050, and the demand for energy to cool buildings will triple.

But unless the energy comes from renewable sources, all that added demand will generate more greenhouse gas emissions, which contribute to global warming – and of course, to hotter summers. It’s a vicious cycle – but buildings can be designed to keep the heat out, without contributing to climate change.

1. Windows and shading

Opening windows is a common way people try to cool buildings – but air inside will be just as hot as outside. In fact, the simplest way to keep the heat out is with good insulation and well-positioned windows. Since the sun is high in summer, external horizontal shading such as overhangs and louvres are really effective.

East and west facing windows are more difficult to shade. Blinds and curtains are not great as they block the view and daylight, and if they are positioned inside the window, the heat actually enters the building. For this reason, external shutters – like those often seen on old buildings in France and Italy – are preferable.

2. Paints and glazes

It’s now common for roofs to be painted with special pigments that are designed to reflect solar radiation – not just in the visible range of light, but also the infrared spectrum. These can reduce surface temperatures by more than 10°C, compared to conventional paint. High performance solar glazing on windows also help, with coatings that are “spectrally selective”, which means they keep the sun’s heat outside but let daylight in.

There’s also photochromic glazing, that changes transparency depending on the intensity of the light (like some sunglasses) and thermochromic glazing, that becomes darker when it is hot, which can also help. Even thermochromic paints, which absorb light and heat when it’s cold, and reflect it when it’s hot, are being developed.

3. Building materials

Buildings which are made of stone, bricks or concrete, or embedded into the ground, can feel cooler thanks to the high “thermal mass” of these materials – that is, their ability to absorb and release heat slowly, thereby smoothing temperatures over time, making daytime cooler and night time warmer. If you have ever visited a stone church in the middle of the Italian summer, you will probably have felt this cooling effect in action.

Cooler inside than out. Image: Blaster/Flickr/creative commons.

Unfortunately, modern buildings often have little thermal mass, or materials with high thermal mass are covered with plasterboard and carpets. Timber is also increasingly used in construction, and while making buildings out of timber generally has lower environmental impacts, its thermal mass is horrendous.

4. Hybrid and phase change materials

While concrete has a high thermal mass, it’s extremely energy intensive to produce: 8 per cent to 10 per cent of the world’s carbon dioxide (CO₂) emissions come from cement. Alternatives such as hybrid systems, composed of timber together with concrete, are increasingly being used in construction, and can help reduce environmental impacts, while also providing the desired thermal mass.

Another, more exciting solution is phase change materials (PCMs). These remarkable materials are able to store or release energy in the form of latent heat, as the material changes phase. So when it’s cold, the substance changes to solid phase (it freezes), and releases heat. When it becomes liquid again, the material absorbs heat, providing a cooling effect.

PCMs can have even greater thermal mass than stones or concrete – research has found that these materials can reduce the internal temperatures by up to 5°C. If added to a building with AC, they can reduce electricity consumption from cooling by 30 per cent.

PCMs have been hailed as a very promising technology by researchers, and are available commercially – often in ceiling tiles and wall panels. Alas, the manufacture of PCMs is still energy intensive. But some PCMs can cause a quarter of the CO₂ emissions that others do, so choosing the correct product is key. And manufacturing processes should become more efficient over time, making PCMs increasingly worthwhile.


5. Water evaporation

Water absorbs heat and evaporates, and as it rises, it pushes cooler air downwards. This simple phenomenon has led to the development of cooling systems, which make use of water and natural ventilation to reduce the temperature indoors. Techniques used to evaporate water include using sprayers, atomizing nozzles (to create a mist), wet pads or porous materials, such as ceramic evaporators filled with water.

The water can be evaporated in towers, wind catchers or double skin walls – any feature which creates a channel where hot air and water vapour can rise, while cool air sinks. Such systems can be really effective, as long as the weather is relatively dry and the system is controlled carefully – temperatures as low as 14°C to 16°C have been reported in several buildings.

But before we get too enthusiastic about all these new technologies, let’s go back to basics. A simple way to ensure AC doesn’t contribute to global warming is to power it with renewables – in the hot weather, solar energy seems the obvious choice, but it takes money and space. The fact remains, buildings can no longer be designed without considering how they respond to heat – glass skyscrapers, for example, should become obsolete. Instead, well insulated roofs and walls are crucial in very hot weather.

Everything that uses electricity in buildings should be as energy efficient as possible. Lighting, computers, dishwashers and televisions all use electricity, and inevitably produce some heat – these should be switched off when not in use. That way, we can all keep as cool as possible, all summer long.

The Conversation

Aurore Julien, Senior Lecturer in Environmental Design, University of East London.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 
 
 
 

How can cities become more bike friendly? The Netherlands offers useful lessons

(Aurore Belot/AFP via Getty Images)

It might seem like cycling is in the DNA of the Netherlands, a country where even the prime minister takes his bicycle to work. But the Dutch haven’t always lived as one with their bikes. In the Amsterdam of the early 1970s, cars were considered the wave of the future. They can be seen filling up squares and streets in historical photographs, and killed an average of over two Amsterdammers per week, including many children.

It is nothing more than an “accident of history” that the Netherlands embraced cycling, says Marco te Brömmelstoet, the director of the Urban Cycling Institute in Amsterdam and a man better known as the city’s cycling professor. Today’s bike rider’s paradise was created after parents and activists took to the streets to protest “child murder” by car. A Saudi oil embargo, rising gas prices, concerns about pollution and anger about the destruction of entire neighbourhoods to build motorways did the rest. 


Amsterdam, 1958. Not a cyclist's paradise. (Keystone/Getty Images)

What’s important about this history is that it can be replicated in other cities, too. Of course, the Netherlands has certain advantages – it’s flat as a pancake, for example. But in the eyes of traffic reformers, the rise of e-bikes (and even cargo bikes) means there’s no excuse for prioritising cars everywhere. 

So how can cities, flat or not, follow Amsterdam’s path to creating places where cycling is a pleasant, safe and common way to get around? The Dutch have some tips. 

Separate bikes from car traffic

Any city could start painting dedicated bike lanes on the streets. But in the Netherlands, those white marks indicating space for cyclists are considered just a minor first step. 

“A line on the road is not enough. Motorists will ignore it,” says Frans Jan van Rossem, a civil servant specialising in cycling policy in Utrecht. If other cities want their residents to choose bikes instead of cars when dodging pandemic-era public transport, protecting them from fast-moving car traffic must be the priority, Van Rossem says. 

The Dutch research institute CROW developed a widely praised design manual for bicycle infrastructure, full of tips for creating these protected lanes: A row of vertical white posts or a curb can serve as a physical separator, for example. Still, cyclists tend to feel safest in a "solitary" path, separated from the road by grass, trees, or an elevated concrete island. 

“The main bottleneck, the main reason why people don’t cycle, is that they don’t feel safe,” Van Rossem notes. “To start, construct separate paths.”

Turn those bike paths into a network

Many cities may have some bike lanes on some streets, but leave cyclists to roll the dice everywhere else. Will conditions still be safe when they turn left or right? Often they have to continue their way without any protected facilities for cyclists. 

“In many cases, cities take fast action, without thinking it through very well,” says Lucas Harms. He leads the Dutch Cycling Embassy, a partnership between the Dutch government and several companies, which promotes Dutch bike knowhow globally. “Don’t build small pieces of bike lane from nothing to nowhere. Think about a network of cycling infrastructure.” 

Utrecht aims to have cyclists within 200 to 300 metres of a connected path anywhere in the city, Van Rossem says. Avoid constructing those paths in sketchy industrial areas, he warns. “A connection through an unattractive area may be fast, but won’t be used a lot.”

Embrace the ‘fietsstraat’, a street where bikes come first


On some streets, drivers have to give up their privileges. (Rick Nederstigt/AFP via Getty Images)

A peculiar Dutch invention called "fietsstraat" (cycling street) holds strong potential for the rest of the world, Kevin Krizek says. He’s a transportation professor from Colorado who spent three years at Radboud University in Nijmegen. 

On cycling streets, cars are “guests”, restricted by a speed limit of 30 kilometres per hour. Drivers are not allowed to pass, so cyclists comfortably dominate the road. In the Netherlands the fietsstraat is usually paved with red asphalt, to resemble a bike path and notify drivers of their secondary status. But creating a cycling street can be easy. “All you need to do is put signs at intersections,” Krizek says. The effect is revolutionary in his view. Drivers have to give up their privileges, and cyclists can take the lead. 

Some Dutch traffic experts worry the cycling street won’t work if a city doesn’t also have a robust cycling culture. In the Netherlands, drivers are aware of the perils of urban cycling because they too use bicycles. Moreover, Dutch cities use sophisticated “circulation plans” to direct cars away from city centres and residential areas, onto a few main routes. 

Without “calming” traffic this way, the cycling street could be a step too far, Harms says. “In a city like New York, where all roads are equally accessible and full, it’s better to separate bicycles and cars,” he says.

Redesign intersections for cyclists' safety

If cyclists have to cross intersections “at the mercy of the Gods”, you’re not there yet, says Harms. When he travels abroad, he often finds clumsily designed crossings. As soon as cars turn, cyclists may fear for their lives. 

Harms recommends placing physical barriers between cars and bikes in places where they must cross. The Dutch build elevated islands to direct traffic into separate sections. The golden rule: cars wait behind bicycles. That way, drivers can see cyclists clearly at all times. Barriers also force Dutch cyclists to turn left in the safest way possible. They cross the street first and wait for their turn again before making their way left.

“You can create that with simple temporary measures,” Harms says. Planters work fine, for example. “They must be forgiving, though. When someone makes a mistake, you don’t want them to get seriously injured by a flower box’s sharp edge.”

Professor Krizek points out how the Dutch integrated cycling routes into roundabouts. Some are small; some are big and glorious, like the Hovenring between Eindhoven and Veldhoven, where cyclists take a futuristic-looking roundabout lifted above the highway. Most of those traffic circles move high volumes of cars and cyclists through intersections efficiently and safely. For a simpler solution, the Dutch manual suggests guiding cyclists to quieter streets – crossing a block up or down may be safer. “Nobody knows how to do intersections better than the Dutch,” says Krizek. 

Ban cars, or at least discourage them


A man rides down from a three-level bicycle parking garage near Amsterdam's main train station. (Timothy Clary/AFP via Getty Images)

The quickest, most affordable way to make a city more bikeable is to ban cars, says Ria Hilhorst, cycling policy advisor for the City of Amsterdam. It will make streets remarkably safe – and will most likely enrage a significant amount of people. 

Amsterdam doesn’t outlaw cars, but it does deliberately make their owners feel unwelcome in the historic city’s cramped streets. Paid parking is hugely effective, for example. Many car owners decide to avoid paying and use bicycles or public transportation for trips into the city. Utrecht, meanwhile, boasts the world’s largest bicycle parking garage, which provides a dizzying 12,500 parking spots.

To further discourage drivers from entering the city’s heart, Amsterdam will soon remove more than 10,000 car-parking spaces. Strategically placed barriers already make it impossible to cross Amsterdam efficiently by car. “In Amsterdam, it is faster to cross the city on a bike than by car,” Harms says. “That is the result of very conscious policy decisions.”

Communicate the benefits clearly

Shopkeepers always fear they will lose clients when their businesses won’t be directly accessible by car, but that’s a myth, says Harms. “A lot of research concludes that better access for pedestrians and cyclists, making a street more attractive, is an economic boost.”

Try replacing one parking space with a small park, he recommends, and residents will see how it improves their community. Home values will eventually rise in calmer, bike-friendlier neighbourhoods without through traffic, Van Rossem says. Fewer cars mean more room for green spaces, for example.

“I often miss the notion that cycling and walking can contribute a lot to the city. One of the greatest threats to public health is lack of exercise. A more walkable and bikeable city can be part of the solution,” says Ria Hilhorst. “But in many countries, cycling is seen as something for losers. I made it, so I have a car and I’m going to use it, is the idea. 

“Changing this requires political courage. Keep your back straight, and present a vision. What do you gain? Tranquility, fewer emissions, health benefits, traffic safety, less space occupied by vehicles.” 

Again, she points to Amsterdam’s history. “It is possible; we were a car city too.”

Karlijn van Houwelingen is a journalist based in New York City.