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How to cool homes without heating the climate

As global temperatures rise, so does the demand for air-conditioning, which guzzles energy and emits greenhouse gases. The race is on to find alternatives – which could be refreshingly low-tech

Author: Clare Dowdy

06 January 2021

Illustration: Masha Krasnova-Shabaevaon

Climate change means more heatwaves, which in turn means more air-conditioning units. Or, at least, that is the prediction. The energy demand by AC units around the world is expected to triple by 2050, reports the IEA (International Energy Agency). In India alone, only 8% of the country’s 249 million households currently have AC, according to the Bureau of Energy Efficiency in New Delhi, but this figure is expected to rise to 50% by 2050.

As well as guzzling huge amounts of electricity, older AC units contain refrigerants such as hydrochlorofluorocarbons (HCFCs), which are potent greenhouse gases. These are the fastest-growing source of greenhouse gas emissions in every country on Earth, and have a global warming potency 2,000 times that of CO2, according to the UN Environment Programme.

Under the 1987 Montreal Protocol, developed countries agreed to phase out HCFCs by 2030, with developing countries agreeing to following suit. But hydrofluorocarbons (HFCs), which were introduced as non-ozone-depleting alternatives to HCFCs, are straining efforts to stall the rise in global temperature because of their own high CO2 emissions. In 2016, the signatories of the Montreal Protocol agreed to gradually reduce HFCs by 80-85% by the late 2040s.

What’s the alternative?

These measures mean that around the world, the pressure is on to seek ways to wean households off AC units. The solutions on offer loosely fall into two categories: first, passive options reduce solar gain by stopping the heat getting indoors in the first place; second, active cooling strategies or mechanical ventilation cool the air once it’s in.

Many passive solutions seem refreshingly low-tech, cheap and simple. And many of them involve apertures – their positioning, size, number, glazing, dressing and design.

Windows can let in about 25% of summer heat. “Closing the blinds or curtains during the sunniest hours can help block this heat,” says Abdullatif N Albitawi, independent consultant and honorary vice-chairman of the Energy Institute Middle East (EI-ME).

Meanwhile, semi-permanent window films tint the glazing and let less heat in. However, in northern countries, that lessens the amount of useful daylight, which can detrimentally affect residents’ moods and can increase energy consumption in winter. “It’s not [a solution] I really recommend,” says Tariq Abbas, associate director in the energy and sustainability division at HurleyPalmerFlatt.

External shading, such as metal louvres or vertical fins, are common on blocks of flats in continental Europe. This is expensive and permanent – meaning, again, that the heating will need to be turned up in chillier winter months.

 

Retractable shading in Barcelona, Spain

Alternatively, there’s the retractable external shading system. “Think of Barcelona,” says Charles Blaschke IV, director of development and innovation at Taka Solutions in Dubai. Awnings allow energy gains in winter and can work well on low-rise homes, but on high rises, the fabric can rip in the winds that blow up and down the sides of buildings, Abbas cautions. “We need to find better ways to apply them to towers. I’d like to see the industry have a step change in the type of technology used here,” he adds.

Abbas points out that: “If you’ve got punched windows, and if they’re recessed, you don’t need shading.” But it’s very expensive to retrofit recessed windows, and would involve gutting the building.

Windows aren’t the only answer to the problem; artificial lighting has a role to play, too. Albitawi suggests ditching incandescent lamps in favour of LED or fluorescent lamps. This “not only reduces the electricity used in lighting but also reduces the amount of heat generated”.

Ceilings also have potential. Exposing the soffits reveals the concrete above, which, with its high thermal mass, takes longer to heat up than other surfaces. But, while that might work in an industrial-chic co-working space, it poses aesthetic challenges in a home. On a practical note, however: “The height increase is beneficial because heat wants to rise,” Abbas explains. What’s more, “if you have a window that’s hinged in the middle, the heat will go out through the top, and will draw cool air through the bottom".

Another easy and effective measure is to weather-strip the areas around doors. “It keeps cool air from escaping,” says Waddah S Ghanem Al Hashmi, director (ENOC) and honorary vice-chairman of the EI-ME. “However, it is important to have a balance between keeping the home cool and good ventilation.”

Old-school cooling

Some of these solutions are born of traditional building techniques. “Interestingly, the further back you go in the building stock, the better the buildings are [at keeping themselves cool],” says Blaschke. That’s because of “deep windows, small windows, external shading and siting with less southern exposure”.

 

Windcatchers in Yazd, Iran... and a modern prototype designed for Dubai Design Week in 2019. Image courtesy of MAS

Other historic, regional-specific, techniques are now also being reconsidered. Blaschke points to the barjeel (windcatcher), popular in medieval Persia, with Yazd in Iran still known today as “windcatcher city”. They combine wind towers and rain-filled cisterns to cool buildings in hot weather. Wind comes through the towers’ windows, and that air is directed over the cistern and out through the downward cooling tower. As the cistern water evaporates, the air in the building is cooled. 

Albitawi points out that just a few wind towers have continued to be used, “more, we believe, influenced by the passion of some of the architects in the region. Some work has been done by a few very passionate architects such as Peter Jackson, Anne Coles and Rashad Bukash.” Some of these architects have attempted to reintroduce windcatchers in residential housing projects in the UAE and abroad. “The reintroduction has been slow, and it is more from an aesthetics drive than an energy saving design,” Albitawi adds.

“Interestingly, the further back you go in the building stock, the better the buildings are” Charles Blaschke IV, Taka Solutions
The cooling effect of plants

As well as interventions in existing housing stock, Al Hashmi recommends vegetation as one of the most effective ways to reduce heat-island effects. “Planting trees or vines near exterior walls reduces the temperature by blocking the sunlight that heats them up.” Likewise, rooftop planting reduces the amount of heat absorbed by the roof. By reducing heat-island effects, the building needs less cooling, as residents of the verdant Chinese city of Chengdu know. Milan and Melbourne are following suit, with vast tree-planting schemes planned.

Away from passive cooling, current mechanical solutions – fans, pumps, compressors – all need fuel, although, as our use of renewable electricity increases and our carbon emissions fall, these options will do less damage to the planet. And mechanical cooling has advantages in noisy or polluted areas, where opening a window generates its own problems.

While all these solutions come with advantages and disadvantages for existing homes, it’s worth remembering that AC units are popular among residents because of their high cooling capacities and fast temperature regulation. Their downsides include the disturbing draft that convection creates, their visibility and noise and, of course, their high operating costs.

 

Rooftop planting in Chengdu, China

Adopting smart technologies

Rather than replacing air conditioning units’ greenhouse gas emissions with another problematic substance, the Montreal Protocol talks of reducing our dependency on high-GWP (global warming potential) alternatives, and increasing the adoption of low-GWP, energy efficient technologies. “Such a ‘smart approach’ can achieve the protocol’s objective of eliminating HCFCs while at the same time achieving energy efficiency gains and CO2 emissions reduction — a ‘climate co-benefit’,” reads the protocol.

Technology and smart design are increasingly stepping in to offer their own solutions. Al Hashmi cites active solar cooling, which uses solar thermal collectors (such as solar panels) to provide solar energy to thermally driven chillers. The collector converts solar radiation into mechanical work, a refrigeration or air-conditioning plant produces the cooling, and a heat sink collects any rejected heat and radiates it away from the system. Small cooling units for houses have become more available, which has increased interest in regions including Central Europe, Australia, the Mediterranean islands and the Middle East.

Surface cooling systems

Alternatively, surface cooling “is not only more effective than conventional cooling, but also offers more elegant and contemporary design possibilities”, Al Hashmi adds. In this system, cold water is circulated through pipes embedded into the walls, floors or ceilings. Increasingly popular in new-builds in Europe, there are now versions (such as thin film systems) that can be retrofitted without massive interventions. This gets around the problem of increasing floor levels, which in turn can cause problems for the door height or power outlet, and the load-bearing capacity of ceilings may not be up to it.

Either way, the surface-cooling infrastructure is unobtrusive, and switches to become the heating system when the weather turns, by pumping not cold but hot water through the pipes. And because they are installed over a large area, the cooling effect is evenly distributed around the room. That means they can achieve a perceived reduction in heat at a lower temperature, thereby offering energy savings.

Meanwhile, if smart monitoring and control technologies can be introduced, they more accurately monitor temperature and humidity “and thus allow for more efficient operations to cool buildings”, says Albitawi. Blaschke agrees about the benefits of a data-driven control of systems, adding that they allow for “automated, demand-based cooling where it is needed and when it is needed, no more”.

For many in the industry, the AC alternative will be a combination of a number of techniques rather than a silver bullet, because, as Abbas says: “It’s a trade-off [between factors including] useful daylight, economics and planning.”

“Surface cooling is not only more effective than conventional cooling but also offers more elegant design possibilities” Waddah S Ghanem Al Hashmi, EI-ME

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