Our reliance on air conditioning is set to increase dramatically, driven by climate change, higher living standards and rises in populations.
By 2050, World Bank forecasts show, the number of air-conditioning units around the globe is set to triple to five billion.
“The demand for cooling will go up, not just because of increasing temperature, but because we haven’t built to house all the projected population growth and economic activities in the developing world,” says Monjur Mourshed, professor of sustainable engineering at Cardiff University in the UK.
“And the way we have been building in the developing world, I don’t necessarily think they are very sustainable.”
Cardiff University
There is concern that buildings in warmer countries rely too much on air conditioning instead of natural cooling, and may have features, such as glass-covered facades, that cause them to heat up.
Characteristics that reduce energy consumption may be “engineered out” of buildings to lower costs.
Because of the extreme climate, few countries need air conditioning more than the UAE, where the technology has been estimated to account for as much as 70 per cent of electricity consumption.
In other nations the cooling or heating of buildings also takes up a significant share of power consumption, such as about 40 per cent in the US.
Yet there are ways to reduce temperatures without switching up the air-con.
Here The National looks at the options and asks experts how present-day architects and building engineers can use them.
Limiting temperature fluctuations
In very hot climates, it is beneficial to have buildings that do not change temperature easily, as this limits daytime temperature increases.
Buildings in Greece, for example, are designed, painted and furnished in ways that reduce temperature swings, says Prof Malcolm Cook, professor of building performance analysis at Loughborough University in the UK.
“They’re white, they’re concrete and they’ve got no soft furnishings,” he says. “That’s because they want to use the stone to absorb the heat.”
Also, thicker walls giving the buildings a higher thermal mass, which evens out temperature fluctuations.
Traditionally this has also been employed in the Gulf, as well as in many other hot regions of the world, but modern buildings often fail to make use of this effect.
An exception is Qatar’s Msheireb Downtown Doha, which is currently under construction. This development includes a focus on high thermal mass buildings.
Phase-change materials
While some approaches to passive cooling rely on traditional techniques, others like phase-change materials are based on the latest technology.
These materials move from one physical state to another, following the principle that, when substances melt or evaporate they absorb heat, while when they condense or solidify they release heat.
“These help to maintain a steady temperature,” says Prof Mourshed.
“In the desert the night temperature goes down significantly. If there might be a way to take that into account, there might be a way to lower the demand on mechanical cooling.”
Phase-change materials from the chemical company BASF have been trialled in plasterboard at an “eco house” at the University of Nottingham in the UK.
The plasterboard contains Micronal, a material of microscopic wax particles enclosed in a polymer shell. Rising temperatures melt the wax, which draws in heat and cools the air.
As temperatures cool, the wax solidifies and releases this heat.
Ventilation
Traditionally, buildings in the Gulf have been cooled using wind towers, or barjeel, which draw air up from inside the building, and funnel down outside air. Dubai’s Al Fahidi or Al Bastakiya neighbourhood is known for its wind towers.
If a room has two openings to the outside, only one of which need be a window, a similar effect can be achieved: cooler air comes in through the lower opening, while warmer air leaves from the upper opening.
Cross-ventilation, in which windows are lined up so that air flows in through one and out through the other, is another strategy.
However, it is difficult to use the cooling effect of natural ventilation in high-rise buildings, because increased wind speeds at height can make opening windows hazardous.
As well as employing various passive cooling approaches, designers can focus on the indoor “micro-environment”, of cooling the occupant rather than the building, says Dr Anna Mavrogianni, associate professor in sustainable building and urban design at University College London.
“This could be achieved by introducing personal comfort system (PCS) technologies, such as small-scale fans, small-scale evaporative systems, cooled chairs or desks, and encouraging flexible dress codes in the workplace,” she says.
Smart systems in buildings are another way of cutting energy use.
Heat exchangers
Another approach is ground-coupled ventilation, which does more than create airflow.
By making use of the fact that the temperature below ground stays relatively constant, in warmer climates it cools air brought in from outside.
“If you could bring air through [the ground], then air cools down to the [ground] temperature, which is very close to thermal comfort level. You reduce the reliance on mechanical means to cool the building,” says Prof Mourshed.
Broadmeadows Primary School, built about ten years ago near Melbourne in Australia, offers a good example, with air being drawn in from intakes outside the building before it travels through pipes laid inside water-filled trenches within the foundations.
The water takes heat from the air and can reduce its temperature by more than 20°C.
This has parallels with a traditional method of cooling in the Middle East. Qanats are underground water channels that cool air as it is drawn in. The air then leaves via a wind tower.
Reflection and shading
Light colours reflect sunlight, so some roads in Los Angeles have been painted white to reduce the urban heat island effect, which causes cities and towns to be hotter than surrounding countryside.
Photochromic glazing – a form of tinted glass – can be used in buildings to reduce the heating effect of the sun.
“It reduces the penetration of direct sun gain, but enables daylight to come,” says Prof Cook.
Matthew Tribe, Dubai-based principal at CallisonRTKL, an architecture, planning and design firm, says orienting the facade of a building to reduce sunlight can cut heat gain.
Inward-facing courtyards can maximise shading, as do mashrabiya, windows with wooden latticework.
“External shading mechanisms, such as external shutters, horizontal overhangs and awnings, are particularly effective in reducing indoor temperatures, especially for south-facing spaces,” says Dr Mavrogianni.
“Their main advantage is that they block solar heat gains before they penetrate the building fabric and are, thus, more effective than internal shading systems.”
In modern buildings, shading can alter according to the time of day, with the more than 1,000 hexagonal shades on Al Bahr Towers in Abu Dhabi closing when the sun is overhead.
Narrow streets and short distances
Towns in the Gulf have traditionally had narrow streets, as their heavy shading reduces temperatures and makes it easier for people to reach their destination by foot.
Mr Tribe said Callison RTKL was not involved with Msheireb Downtown Doha but that it takes a similar approach.
“It set out very early on with the ambition to create a contemporary interpretation of a traditional district,” says Mr Tribe.
Buildings at Msheireb Downtown Doha are low-rise but close together to maximise shade and have a high thermal mass to limit temperature changes.
Shops, offices and homes are within walking distance of one another to reduce car journeys, also echoing the traditional town.
