The world is getting hotter, and the most common technologies to cool down our homes are making things worse. In a new special issue of the journal Science, researchers have identified key ways to get us out of that catch-22. They include cutting-edge technologies and materials that could fundamentally change air conditioning for the better.
One of the most commonly used cooling technologies on Earth is vapor compression refrigeration, which essentially uses a heat engine but runs it backwards. Normally, heat flows from hot places to cold places, but this method uses a heated refrigerant liquid which is able to pull heat from a warm place instead. Another version of the process can be used to heat homes, too.
In one study published in the new issue, scientists explain that though this refrigeration is highly effective and has even been called one of the most important engineering feats of the 20th century, it’s extremely energy intensive. That’s an issue for our fossil fueled world. In addition, cooling technologies that rely on it traditionally use harmful, ozone-depleting chemicals including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and more recently, their relative, hydrofluorocarbons (HFCs). The latter are potent greenhouse gases, creating another avenue for cooling technologies to heat the planet.
Concern about the planet-damaging potential of these compounds has sparked international treaties and research into alternatives. In the study, the scientists explain that more climate-friendly and efficient refrigerants are being developed to use in vapor compression.
“The development of new fluids has focused on fluorinated olefins, known as hydrofluoroolefins (HFOs), and blends that contain HFOs,” the study says.
Unlike CFCs and HFCs, the new refrigerants have no ozone depletion potential and a far lower global warming potential, making them relatively environmentally safe. But they don’t come without risks to human safety. HFOs create a compound called trifluoroacetic acid when they break down that could cause environmental damage, and many HFOs and HFO blends are flammable. So are some naturally occurring chemicals like ammonia and propane, which are also sometimes used in vapor compression refrigeration. And these natural chemicals can be toxic when they leak, too.
Of course, vapor compression technology isn’t the only way to keep cool in our warming world. Another study in the new issue of Science explores how caloric materials—solids that generate heat when they’re electrically, magnetically, or mechanically manipulated—can be used for cooling or heating homes.
“In a way, caloric materials are analogous to traditional gas refrigerants, where an applied pressure drives a transition from gas to liquid phase, and this leads to changes in temperature in the refrigerant,” Xavier Moya, a materials scientist at the University of Cambridge and an author of the study, said in an email. But unlike traditional cooling, the materials used in this process always remain solid, rather than turning into a polluting gas.
In the study, Moya and his coauthor wrote that there have been massive strides in this field in the past five years, including developing infrared imaging alongside the caloric cooling materials to get an image of the way the technology is changing temperatures in real time. Researchers have also discovered new caloric materials, including a kind of plastic crystal made of a compound called neopenenyl glycol and commonly used in paints and lubricants, which for the first time has produced the same degree of temperature change that traditional cooling does.
But these new technologies are no panacea. The production and disposal of neopenenyl glycol, for instance, can lead to environmental damage. Another commonly used material in the caloric process, neodymium magnets, require using a rare earth mineral which can be environmentally damaging to extract. And there’s also the issue of money. Moya said caloric materials for this process are currently “relatively costly because components are not manufactured at scale.”
Not all cooling technology works by actively heating up chemical compounds. In a third study, scientists describe how passive radiative cooling materials can be used to release heat into space. These materials, sometimes called super-cool materials, can be pointed at the sky to reflect back infrared rays from the sun, keeping them up to 18 degrees Fahrenheit (10 degrees Celsius) cooler than the air around them. The authors detail how researchers are developing these technologies to be used on roofs.
These technologies are promising, but they don’t work in all climates. The materials’ cool best when there’s not much humidity in the air or clouds in the sky. Scientists are also still looking to develop roofs made of these materials that won’t degrade quickly.
These new technologies all show potential for the future of keeping buildings cool, which will become increasingly important in the face of increasingly frequent heatwaves and rising average temperatures. But of course, there are lower-tech ways to cool homes, too, like planting trees to provide shade, strategically placing chimneys atop homes to draw in the cooler breezes that swoosh around above buildings, and even fans. Relying on these may not be as exciting as the pining for breakthrough technology. But just because they’re not as cool—or super-cool—doesn’t mean they shouldn’t have a place in our increasingly sweaty world.