Does opening windows at night keep buildings cool during heat waves? Here's what study says
Washington, Jun 28: Opening the windows at night and pulling down shades during the sunniest part of the afternoon can keep homes from becoming dangerously hot during extreme heat waves, according to a study conducted in the US.
Researchers from the University of Oregon in the US employed simulations using weather data from a 2021 severe heat wave especially in the Pacific Northwest. They found that a combination of shading and natural ventillation kept apartment temperatures out of the danger zone during the entirety of the three-day event, even without air conditioning. It also reduced the load on air conditioning by up to 80 per cent.
The findings, published in the journal Applied Energy, could inform building codes to protect renters from the effects of severe heat. Cities could mandate that apartments have operable windows that can be safely left open overnight, as well as working shades, the researchers said.
"In the Pacific Northwest, where we get such cool night air, we have an amazing climate for passive cooling," said Alexandra Rempel, a building scientist at the University of Oregon who led the study. "And we should take advantage of it,” Rempel said. In June 2021, an extreme heat wave roasted Oregon and Washington.
Temperatures hit 46.7 degrees Celsius in Portland and 143.9 degrees in Eugene, breaking previous records. The prolonged heat was deadly, and the impact was especially great on people living in apartments in dense urban areas, the researchers said. Such extreme heat events are only expected to become more frequent thanks to climate change, they said.
However, buildings in the Pacific Northwest are usually designed to keep heat in. Many homes don't have air conditioning, given the typically mild summer weather, or only have window units. While strategies like drawing the blinds and opening the windows are time-tested ways to cool down homes, there wasn't much solid evidence showing whether they could make a meaningful difference in the face of triple-digit temperatures, Rempel said.
Armed with weather data collected from cities like Eugene, Portland and Seattle during the 2021 heat wave, the researchers used a computer programme to simulate conditions inside a hypothetical west-facing, two-bedroom apartment with different cooling strategies. "Without any shades or ventilation, you'll quickly be in danger zone," said undergraduate student Jackson Danis, a co-author of the study. But even opening windows a little bit lessened the amount of time the apartment was dangerously hot, the researchers said.
Strategically using a combination of passive cooling techniques could make the apartment surprisingly livable, even in the face of triple-digit outdoor temperatures, they said. Opening the windows made the biggest difference at night and in the early morning, when the outside air is the coolest, researchers found.
Meanwhile, using blinds or window shades helped the most during the late afternoon, when the sun was directly shining on the windows, they said. Thick outdoor shades were most effective, but standard indoor pull-down shades or blinds, which renters are more likely to have, still made a difference, especially if their edges were sealed with side tracks.
The impact was even greater with a fan in the window to help circulate air, according to the study. While the advice seems intuitive, "the magnitude of the improvement is something that we didn't expect," said Alan Rempel, an applied mathematician and a co-author of the study. Passive cooling strategies can be a lifeline for people without air conditioning, the researchers said.
However, even people with AC could use the techniques to lower their summer energy bills, added Michael Fowler, a building scientist at the Seattle firm Mithun Inc. who co-directed the study.