How to cool homes without heating the climate

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.

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.”

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.

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

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.

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.”