Heat: What's the alternative to air conditioning?

Kuwaiti summers are oppressive. Baking heat radiates from every corner of the city, making even the lightest of exercise excruciating. That is, unless you are lucky enough to live in an air-conditioned bubble. 

"In Kuwait, you're in your air-conditioned apartment or your air-conditioned car to go to your air-conditioned place of work or the air-conditioned mall," said Alexander Nasir, who used to live in the Gulf nation. "Of course it was absolutely atrocious for the environment, but it was the only way to avoid the inferno outside."

Nasir moved to Berlin in 2014, but he hasn't been able to escape sweltering temperatures. Though the German capital has much milder summers, he has already experienced heat waves of up to 38 degrees Celsius (100 Fahrenheit) — temperatures that felt more intense because German homes are rarely air-conditioned.  

"I can't and don't want to resort to AC again," he said, speaking to DW in 2022. "But it's getting worse every year and we're not really adapting." 

Demand for space cooling is soaring 

The climate crisis has made heat waves more likely and more intense around the world. The summer of 2023 saw soaring temperatures worldwide, with NASA saying July was the hottest ever recorded.  

Even in 2018, the use of air conditioners and electric fans made up 10% of global electricity consumption, according to the International Energy Agency.

AC units are only widespread in a few countries like Japan and the United States — where more than 90% of households have them. They're only available to 8% of people in the hottest parts of the world.  

But as the summers get hotter demand for space cooling is soaring, especially in emerging economies. Electricity demand could more than triple by 2050.

In much of the world, air conditioners are powered by fossil fuels, which emit greenhouse gases and make the planet hotter.  

"It's a vicious loop. We cool the indoors, but we warm the outdoors, therefore generating the need for more cooling," said Sneha Sachar, Associate Director at Clean Cooling Collaborative, an initiative aimed at transforming the cooling sector. 

To break out of this loop, scientists point to passive cooling strategies that control temperature using little to no energy.  

"Passive cooling is so promising because it's less expensive, it averts intensification of urban heat island effects, it increases survivability by diminishing reliance on air conditioning," said Alexandra Rempel, assistant professor of environmental design at University of Oregon in the US.

"It also takes pressure off the electrical grid."

Simple solutions for increased cooling without electricity

Sometimes, cooling a home can be as simple as opening the windows at night to let in cool air and drawing the shades when the sun hits the window during the day.   

Rempel authored a study that found natural ventilation and shading alone can lower indoor temperatures by about 14 C and reduce the load on air conditioners by up to 80%. The study made these simulations using data from a 2021 heat wave that killed hundreds in the Pacific Northwest region, usually known for its mild weather.   

Old cooling tricks can make a significant difference if they are communicated properly and facilitated, according to Rempel. This shows the Pacific Northwest, one of the few US regions where air conditioners aren't yet ubiquitous, can avoid adopting air conditioning or at least minimize it even as extreme heat becomes more likely, she said. 
 

Designing more energy efficient buildings for warmer climates 

Passive cooling can also be integrated into a building's design. Some methods, such as wind catchers in North Africa and the Middle East, have been staving off heat for centuries. 

These towers with open windows are positioned on top of buildings and, as the name suggests, are made to "catch" the wind. They direct the fresh air indoors and push the warm air back out through the tower. Though traditional wind catchers are largely out of use, commercial models using the same technology can be used in modern buildings. 

Other features that help keep buildings bearable include louvered shading devices that block out the sun, insulation and double glazing that limits the amount of heat gained or lost through windows and water fountains that lower the air temperatures through evaporative cooling.   

India has found that even a simple fix like painting roofs with lime-based white-wash can reduce indoor temperatures by 2 C to 5 C.  

Designing with location in mind is also key, according to bioclimatic architects, whose designs take local climates into account. Studying the wind direction before building allows for openings that encourage cross ventilation, for example. 

"You have to pay attention to the sun orientation and make sure your facades are not exposed to the direct sun. And then we usually study carefully the wind direction," said Charles Gallavardin, cofounder of Kanopea Architecture & T3 Architects. 

These methods can reduce indoor temperatures by about 5 C, according to Gallavardin.  

Reducing heat in cities with more trees and green corridors

But passive cooling isn't only about directly lowering indoor temperatures — it's also about reducing surface temperatures on the buildings and surrounding areas. Because it's not easy to stay cool in concrete jungles with little shade.  

"When the streets and sidewalks are just basking in heat all day, those materials are perfect thermal storage mass and continue to radiate heat back to the environment all night," said Rempel. "So that takes away some of the night ventilation resources and makes air conditioners work harder." 

The solution to that is straightforward: more trees, more shade.

In Medellin, Colombia, authorities have planted "green corridors," vegetated passages keeping pedestrians and cyclists out of the direct sun. They have helped reduce the city's average temperatures by 2 C.   

In tropical Singapore, dense vegetation on some skyscraper facades keeps them from heating up as much. 

"By having at least 10 meters of greenery on the front of your buildings, you can reduce the surface temperature by 5 degrees Celsius," said Ayu Sukma Adelia, an architect from the Cooling Singapore Research Project. 

District-level cooling 

Another approach is to cool entire districts with massive cooling units. Singapore has what it claims to be the largest underground district cooling facility in the world, which brings temperatures down in residential buildings, banks, malls and an iconic hotel.  Water is chilled 25 meters below the ground before it is piped across a series of buildings. 

District cooling can save up to 50% on energy and emissions compared to regular air conditioners, and cities such as Toronto, Paris and Hong Kong are now using them. 

For Nasir, who was dealing with another particularly hot day in the sweltering Berlin 2022 summer, the idea of passive cooling sounded appealing. 

"I welcome any solution so I don't have to sweat anymore," he said as he sat in a dark room and sprayed himself with water.

Edited by: Tamsin Walker and Jennifer Collins 

This article was first published in July 2022 and was updated on August 21, 2023 with new information on passive cooling techniques.