Wanted: New ways to chill air conditioners, fridges

The hunt is on for chemicals to keep both you and the planet cool.

A new agreement will soon begin phasing out the powerful greenhouse gases currently used in air conditioners, refrigerators and insulating foams. These gases, called hydrofluorocarbons, or HFCs, can cause hundreds of times more global warming per molecule than carbon dioxide. The phaseout, announced by world leaders on October 15 in Kigali, Rwanda, has scientists and chemical companies investigating new molecules to chill things with less harm to the planet. Some of these molecules are already in use, while others require more tinkering.

Hunting for eco-friendly alternatives to planet-warming HFCs requires careful chemistry, says Rajiv Banavali, a chief technology officer at Honeywell International, which develops chemicals for air conditioners and refrigerators. A replacement chemical has to serve the same purpose without necessitating a major — and costly — redesign of the rest of the product, he says.

Many of the new chemicals are designed to quickly break apart through chemical reactions once in the atmosphere, but function properly when contained. That short lifetime means that any molecular escapees cause warming for only a few days, rather than years or decades like many current refrigerants.

The current generation of coolants arose after the 1987 Montreal Protocol banned chlorofluorocarbons, or CFCs, which were destroying the ozone layer. Retiring those chemicals has helped heal the ozone hole (SN: 7/23/16, p. 6). But many of their replacements, including certain HFCs, are potent greenhouse gases. Right now, those replacement chemicals make up about two percent of greenhouse gas emissions in terms of global warming potential, but that share could increase as air conditioners become more prevalent in developing countries such as India.

The Rwanda deal’s ultimate goal is to reduce usage of HFCs by 80 to 85 percent by 2047, preventing as much as 0.5 degrees Celsius of global warming by 2100.

Several new replacements are in development, including hydrocarbons that trap less heat. Some prototype systems even forgo chemical refrigerants altogether and instead use sound waves to pump heat, though the technology is currently energy inefficient and takes up too much space, says Stephen Yurek, president of the Air-Conditioning, Heating and Refrigeration Institute in Arlington, Va. “There’s a lot of opportunity for new and creative ideas on how to do this,” he says.

One approach already in use is HFO-1234yf, a refrigerant used in car air conditioners. Each molecule contains a double bond between two carbon atoms that serves as an intentional fatal flaw, breaking the molecule apart once it leaks into the atmosphere. The result of a joint venture between Honeywell and chemical company DuPont, HFO-1234yf’s design results in a global warming potential just a few thousandths that of its predecessor.

Even with a short lifetime, a chemical can still contribute to global warming. R-134a was considered as a replacement refrigerant in freezers because it has a small global warming impact once in the atmosphere. The chemical makes the freezer more energy-hungry, though, says chemical engineer Paul Blowers of the University of Arizona in Tucson. In a 2010 paper in Environmental Science & Technology, he calculated that using R-134a would actually increase a freezer’s total climate impact due to the increased energy use.

Some potential downsides, such as reduced energy efficiency, can be tested before implementation, but others can’t, Blowers says. CFCs were invented decades before their link to ozone depletion was established. “Will we make some bad decisions along the way? Yes. Will we fix them? Hopefully faster than we have before,” he says. “This regulation is good because it moves us forward.”

While some hurdles remain, “people see solutions to this problem,” says A.R. Ravishankara, an atmospheric chemist at Colorado State University in Fort Collins. “We don’t usually talk about solutions that are economically viable and that can be instituted quickly when it comes to climate change.” The hunt for climate-friendly refrigerants, he says, “shows that it can be done.”

---

Editor’s note: This story was updated December 6, 2016, to correct the description of the arrangement of the atoms in HFO-1234yf molecules.