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.

 
 
 
 

What Citymapper’s business plan tells us about the future of Smart Cities

Some buses. Image: David Howard/Wikimedia Commons.

In late September, transport planning app Citymapper announced that it had accumulated £22m in losses, nearly doubling its total loss since the start of 2019. 

Like Uber and Lyft, Citymapper survives on investment funding rounds, hoping to stay around long enough to secure a monopoly. Since the start of 2019, the firm’s main tool for establishing that monopoly has been the “Citymapper Pass”, an attempt to undercut Transport for London’s Oyster Card. 

The Pass was teased early in the year and then rolled out in the spring, promising unlimited travel in zones 1-2 for £31 a week – cheaper than the TfL rate of £35.10. In effect, that means Citymapper itself is paying the difference for users to ride in zones 1-2. The firm is basically subsidising its customers’ travel on TfL in the hopes of getting people hooked on its app. 

So what's the company’s gameplan? After a painful, two-year long attempt at a joint minibus and taxi service – known variously as Smartbus, SmartRide, and Ride – Citymapper killed off its plans at a bus fleet in July. Instead of brick and mortar, it’s taken a gamble on their mobile mapping service with Pass. It operates as a subscription-based prepaid mobile wallet, which is used in the app (or as a contactless card) and operates as a financial service through MasterCard. Crucially, the service offers fully integrated, unlimited travel, which gives the company vital information about how people are actually moving and travelling in the city.

“What Citymapper is doing is offering a door-to-door view of commuter journeys,” says King’s College London lecturer Jonathan Reades, who researches smart cities and the Oyster card. 

TfL can only glean so much data from your taps in and out, a fact which has been frustrating for smart city researchers studying transit data, as well as companies trying to make use of that data. “Neither Uber nor TfL know what you do once you leave their system. But Citymapper does, because it’s not tied to any one system and – because of geolocation and your search – it knows your real origin and destination.” 

In other words, linking ticketing directly with a mapping service means the company can get data not only about where riders hop on and off the tube, but also how they're planning their route, whether they follow that plan, and what their final destination is. The app is paying to discount users’ fares in order to gain more data.

Door-to-door destinations gives a lot more detailed information about a rider’s profile as well: “Citymapper can see that you’re also looking at high-profile restaurant as destinations, live in an address on a swanky street in Hammersmith, and regularly travel to the City.” Citymapper can gain insights into what kind of people are travelling, where they hang out, and how they cluster in transit systems. 

And on top of finding out data about how users move in a city, Citymapper is also gaining financial data about users through ticketing, which reflects a wider trend of tech companies entering into the financial services market – like Apple’s recent foray into the credit card business with Apple Card. Citymapper is willing to take a massive hit because the data related to how people actually travel, and how they spend their money, can do a lot more for them than help the company run a minibus service: by financialising its mapping service, it’s getting actual ticketing data that Google Maps doesn’t have, while simultaneously helping to build a routing platform that users never really have to leave


The integrated transit app, complete with ticket data, lets Citymapper get a sense of flows and transit corridors. As the Guardian points out, this gives Citymapper a lot of leverage to negotiate with smaller transit providers – scooter services, for example – who want to partner with it down the line. 

“You can start to look at ‘up-sell’ and ‘cross-sell’ opportunities,” explain Reades. “If they see that a particular journey or modal mix is attractive then they are in a position to act on that with their various mobility offerings or to sell that knowledge to others. 

“They might sell locational insights to retailers or network operators,” he goes on. “If you put a scooter bay here then we think that will be well-used since our data indicates X; or if you put a store here then you’ll be capturing more of that desirable scooter demographic.” With the rise of electric rideables, Citymapper can position itself as a platform operator that holds the key to user data – acting a lot like TfL, but for startup scooter companies and car-sharing companies.

The app’s origins tell us a lot about the direction of its monetisation strategy. Originally conceived as “Busmapper”, the app used publicly available transit data as the base for its own datasets, privileging transit data over Google Maps’ focus on walking and driving.  From there it was able to hone in on user data and extract that information to build a more efficient picture of the transit system. By collecting more data, it has better grounds for selling that for urban planning purposes, whether to government or elsewhere.

This kind of data-centred planning is what makes smart cities possible. It’s only become appealing to civic governments, Reades explains, since civic government has become more constrained by funding. “The reason its gaining traction with policy-makers is because the constraints of austerity mean that they’re trying to do more with less. They use data to measure more efficient services.”  

The question now is whether Citymapper’s plan to lure riders away from the Oyster card will be successful in the long term. Consolidated routing and ticketing data is likely only the first step. It may be too early to tell how it will affect public agencies like TfL – but right now Citymapper is establishing itself as a ticketing service - gaining valuable urban data, financialising its app, and running up those losses in the process.

When approached for comment, Citymapper claimed that Pass is not losing money but that it is a “growth startup which is developing its revenue streams”. The company stated that they have never sold data, but “regularly engage with transport authorities around the world to help improve open data and their systems”

Josh Gabert-Doyon tweets as @JoshGD.