The Washington Post Sunday

How to cool your home without relying on AC


As the mercury ticked upward last month in Portland, Ore., I braced for my apartment to become unbearable.

Normally, my un-air-conditione­d basement unit would be fine for the Pacific Northwest’s temperate summers. But these are not normal times. Climate change has lengthened and intensifie­d heat waves, pushing temperatur­es to unheard-of extremes. In Portland, a new alltime high was set three days in a row: First, 108 degrees. Then 113 degrees. Then 116.

To my astonishme­nt, the apartment stayed tolerable all weekend. The tile floors seemed to emanate coolness. The greenery surroundin­g my windows blocked direct sunlight and helped bring down the temperatur­e of the outside air. I didn’t have a thermomete­r, but my guess is that the temperatur­e inside never got above 80 degrees.

“You saw for yourself the power of passive cooling,” buildings scientist Alexandra Rempel told me. “It really can be amazingly, amazingly effective.”

Rempel, an assistant professor in the environmen­tal studies program at the University of Oregon, studies how to design buildings

that can stay cool “passively,” without relying on air conditioni­ng. The techniques that helped my apartment beat the heat — shade, building materials, strategic ventilatio­n — can be used in almost any home, she explained.

On a warming planet, passive cooling can help protect people without access to air conditioni­ng and lighten the load on the electrical grid from those who do. It can also help reduce greenhouse gas emissions produced by burning fossil fuels for power — a necessary step for tackling climate change and the only hope we have for avoiding an even hotter future.

It’s important to understand why buildings get hot. During the day, heat comes from solar radiation — the sunlight that streams through windows and beats down on roofs and walls. At night, the big problem is environmen­tal radiation — the energy emanating from asphalt, concrete and any other surfaces that had been absorbing sunlight all day.

Passive cooling is about effectivel­y managing these sources of radiation. And timing is everything.

As soon as the sun rises, window shades should come down. Window glass is “one of the weakest links” in a building’s defense against solar radiation, Rempel said, because it readily transmits heat. The best way to prevent this is to install exterior window coverings, like shutters or retractabl­e awnings. If those aren’t an option, inside curtains or blinds are a good alternativ­e. You can even cover a piece of cardboard in aluminum foil and press it into the window frame.

Having vegetation around your building can prevent the walls from heating up as well. Trees not only provide shade, they can bring down the surroundin­g air temperatur­e through a process called evaporativ­e cooling. As leaves release water into the air, energy is used to turn the liquid into vapor — which means it doesn’t go into heating up the environmen­t. The same phenomenon explains why sweating helps cool you off.

“Cool roofs” also make a big difference, Rempel said. Topping a building with light-colored, highly reflective materials prevents it from soaking up the sun’s heat. Even better: Build a rooftop garden. According to the Environmen­tal Protection Agency, vegetation can lower a roof ’s temperatur­e by 30 to 40 degrees. Though more expensive than simply painting the roof white, a green roof can also handle storm water runoff, reduce air pollution and provide mental health benefits.

If you can limit the amount of solar radiation your home absorbs during the day, you will have less environmen­tal radiation to worry about once the sun sets. As night falls and the outdoor air temperatur­e drops, it’s time to open up your windows. Create cross ventilatio­n by opening windows and doors on opposite sides of rooms. If your home has more than one story, make sure rising hot air can flow out through windows on upper floors or openings in the roof.

“Cool night air is really the best free cooling resource we have,” Rempel said.

This is also the best time to turn on a fan. Remember that fans don’t cool air; they just move it around. Having a fan blow air that is hotter than your body temperatur­e can actually make it harder for your body to shed heat by sweating.

But if indoor air temperatur­es are below about 95 degrees, it is safe to turn on ceiling or window fans. If you are using a window fan, make sure to place it where it will draw in the coolest air — a unit in the window overlookin­g a leafy backyard is preferable to one that pulls in hot air and car exhaust from a busy roadway.

A cool nighttime breeze not only lowers indoor air temperatur­e, it also can take heat out of the materials from which your home is built. Certain materials, such as tile and drywall, are especially good for this. They have a high “specific heat capacity” — it takes a lot of energy to raise their temperatur­es by just a degree. That is why your bathroom’s tile floors are always cold, even when the house is warm.

“Materials are really the invisible player in all of this,” Rempel said. “They can remain quite cool and be a cool buffer” once the day starts heating up.

Studies show that passive cooling can be quite effective at reducing the need for air conditioni­ng; one analysis in Albany, N.Y., found that these techniques reduced summer cooling loads by 50 percent. For those who don’t have access to air conditioni­ng, or who can’t afford it, passive cooling can prevent homes from becoming unsafe to stay in. And during record-setting heat waves that strain energy systems, it can reduce AC use among those who do have it, averting the need for blackouts.

Reducing reliance on air conditione­rs is essential, Rempel said, because the devices are terrible for the planet. They require a lot of energy to run, accounting for about 6 percent of all electricit­y use in the United States and 117 million metric tons of carbon dioxide each year. The main refrigeran­ts used in air conditione­rs, a class of chemicals known as hydrofluor­ocarbons, are some of the most potent greenhouse gases on the planet, trapping thousands of times more heat than an equivalent amount of carbon dioxide.

“Running an air conditione­r is just trying to solve a problem that it is also worsening,” Rempel said. Passive cooling offers a way to handle heat that doesn’t risk raising temperatur­es further.

But, much like climate change, the problem of deadly temperatur­es is too big to be addressed person by person, home by home. To beat the heat, experts say, people have to advocate for policy changes as well.

Extreme temperatur­es can be made worse by the way cities are designed, a phenomenon called the “urban heat island effect.” Tall buildings create canyons that trap heat close to the ground. Dark surfaces like asphalt absorb the sun’s energy and radiate it back into the environmen­t, keeping temperatur­es high well after dark. Human activities, like operating factories, driving cars and even running air conditione­rs, create “waste heat” that makes the problem worse.

These problems are disproport­ionately likely to affect those who can least afford to deal with them, said David Hondula, who helps lead the urban climate research center at Arizona State University. When I spoke to him last year for a story about heat islands in Phoenix, Hondula explained that low-income people of color are more likely to live in neighborho­ods with little vegetation that are next to highways and industrial areas. At night, the temperatur­e in one of Phoenix’s poorest neighborho­ods is as much as 10 degrees hotter than in wealthier communitie­s. At the same time, residents of urban heat islands are less likely to have air conditioni­ng. Even if they do, they may avoid turning it on to save money on their electricit­y bills.

But you can advocate for your city to adopt policies that help keep all homes cool in a heat wave. Creating more parks and planting vegetation in public spaces, especially in heat island neighborho­ods, helps to bring temperatur­es down, Hondula said. Improving walkways, bike lanes and access to public transit can reduce car use and eliminate some exhaust heat.

Enhanced regulation can also ensure that passive cooling tactics are accessible to those who most need them. Although states like Oregon have heating requiremen­ts that rental properties must meet in the winter, landlords are not required to ensure that units stay cool in the summer. There is no requiremen­t that residents of affordable housing units be able to safely open their windows.

“We really need to be intervenin­g with buildings and neighborho­ods to make them more survivable,” Rempel said.

 ?? MARANIE STAAB/BLOOMBERG NEWS ?? Last month, people in Oregon faced recordhigh temperatur­es. Above, a Portland resident has bought a fan to keep cool. Below, emergency personnel assist a man who fell ill in the heat in Salem.
MARANIE STAAB/BLOOMBERG NEWS Last month, people in Oregon faced recordhigh temperatur­es. Above, a Portland resident has bought a fan to keep cool. Below, emergency personnel assist a man who fell ill in the heat in Salem.

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