How to cool your home without relying on air conditioning
When the mercury was ticking up in Portland, Oregon last month, I was preparing for my apartment to become unbearable.
Ordinarily, my non-air-conditioned basement unit would be suitable for the temperate summers of the Pacific Northwest. But these are not normal times. Climate change has prolonged and intensified heat waves and driven temperatures to unexpected extremes. Portland hit a new all-time high for three days in a row: 108 degrees Fahrenheit first. Then 113 degrees. Then 116.
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To my amazement, the apartment remained bearable all weekend. The tile floors seemed cool. The green that surrounded my windows blocked out direct sunlight and helped lower the temperature of the outside air. I didn't have a thermometer, but I suspect the temperature inside never exceeded 80 degrees.
"You have convinced yourself of the efficiency of passive cooling," said building scientist Alexandra Rempel. "It can be really amazing, amazingly effective."
Rempel, an assistant professor in the University of Oregon's environmental studies program, is studying how to design buildings that can "passively" stay cool without relying on air conditioning. The techniques that helped my home 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 relieve the grid of those who do. It can also help reduce the greenhouse gas emissions from burning fossil fuels to generate electricity - a necessary step in combating climate change and the only hope we have to avoid an even hotter future.
It is important to understand why buildings get hot. During the day, heat is generated by solar radiation - the sunlight that flows through windows and hits roofs and walls. At night, the big problem is environmental radiation - the energy that comes from asphalt, concrete and other surfaces that have absorbed sunlight all day.
Passive cooling is about the effective use of these radiation sources. And timing is everything.
As soon as the sun comes up, the blinds should go down. Window glass is "one of the weakest links" in protecting a building against solar radiation, said Rempel, because it transfers heat easily. The best way to prevent this from happening is to install exterior window coverings such as roller shutters or retractable awnings. If that's not an option, interior curtains or blinds are a good alternative. You can even cover a piece of cardboard with aluminum foil and press it into the window frame.
Planting around your building can also keep the walls from heating up. Not only do trees provide shade, they can also lower the ambient temperature through a process called evaporative cooling. As the leaves release water into the air, energy is used to turn the liquid into vapor - which means it doesn't heat up the surrounding area. The same phenomenon explains why sweating contributes to cooling down.
"Cool roofs" also make a big difference, says Rempel. Covering a building with bright, highly reflective materials prevents it from absorbing the heat of the sun. Even better: build a roof garden. According to the Environmental Protection Agency, vegetation can lower the temperature of a roof by 30 to 40 degrees Fahrenheit. While it's more expensive than simply painting the roof white, a green roof can also handle rainwater runoff, reduce air pollution, and improve mental health.
If you can limit the amount of solar radiation your house absorbs during the day, you will have to worry less about environmental radiation after sunset. When night falls and the outside air temperature drops, it's time to open the windows. Create cross ventilation by opening windows and doors on opposite sides of the rooms. If your house is multi-story, make sure that the rising warm air can escape through windows on the upper floors or openings in the roof.
"Cool night air is really the best free cooling source we have," said Rempel.
This is also the best time to turn on a fan. Remember, fans don't cool air; they just move it around. In fact, if a fan is blowing air that is hotter than your body temperature, it can make it difficult for your body to dissipate heat through sweating.
But if the indoor air temperature is below about 95 degrees, it is safe to turn on ceiling or window fans. If you use a window vent, make sure it is placed where it draws in the coolest air - a device in the window overlooking a leafy backyard is preferable to a device that draws in hot air and car exhaust from a busy road.
A cool night breeze not only lowers the indoor air temperature, but it can also draw heat away from the materials your home is built from. Certain materials such as tiles and drywall are particularly suitable for this. They have a high “specific heat capacity” - it takes a lot of energy to raise their temperature by just one degree. This is why the tile floors in your bathroom are always cold, even when the house is warm.
"Materials are really the invisible actor in all of this," said Rempel. "You can stay cool and be a cool buffer" when the day starts to heat up.
Studies show that passive cooling can be very effective in reducing the need for air conditioning; Analysis in Albany, N.Y., found that these techniques reduced cooling loads by 50% in the summer. For those who do not have access to or cannot afford air conditioning, passive cooling can keep their homes from becoming unsafe for those who have it to avert the need for blackouts.
Reducing reliance on air conditioning is imperative, Rempel said, because the devices are terrible for the planet. They use a lot of energy to run and make up about 6 percent of all electricity consumption in the United States and 117 million tons of carbon dioxide each year. The main refrigerants used in air conditioning, a class of chemicals known as fluorocarbons, are some of the most powerful greenhouse gases in the world and bind a thousand times more heat than an equivalent amount of carbon dioxide.
"Operating an air conditioner is only trying to solve a problem that is also getting worse," said Rempel. Passive cooling offers a way to deal with heat without raising the temperature any further.
But similar to climate change, the problem of lethal temperatures is too big to be addressed person-to-person, door-to-door. To beat the heat, people must also advocate political change, experts say.
Extreme temperatures can be made worse by the design of cities, a phenomenon known as the "urban heat island effect". Tall buildings form ravines that trap heat near the ground. Dark surfaces such as asphalt absorb solar energy and radiate it back into the environment, which means that temperatures remain high even after dark. Human activities, such as running factories, driving cars, and even running air conditioning, generate "waste heat" which makes the problem worse.
These issues are disproportionately likely to hit those who can least afford to deal with them, said David Hondula, who heads the urban climate research center at Arizona State University. When I talked to him about a story about heat islands in Phoenix last year, Hondula explained that low-income people are more likely to live in areas with little vegetation that are adjacent to highways and industrial areas. At night, one of Phoenix's poorest neighborhoods is up to 10 degrees warmer than wealthier communities. At the same time, residents of urban heat islands are less likely to have air conditioning. Even if you do, you can avoid turning it on to save money on your electric bill.
However, you can campaign for your city to have policies in place that will help keep all homes cool during a heatwave. Creating more parks and planting vegetation in public spaces, especially in neighborhoods with heat islands, will help lower temperatures, Hondula said. Improving sidewalks, cycle paths and access to public transport can reduce car use and eliminate some of the waste heat.
Improved regulation can also ensure that passive cooling tactics are accessible to those who need them most. Although states like Oregon have heating requirements that rental properties must meet during the winter, landlords are not required to ensure that units stay cool during the summer. There is no requirement that residents of affordable housing units can safely open their windows.
"We really have to intervene in buildings and neighborhoods to make them more viable," said Rempel.
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