Current ACs aren’t going to cut it
Over the next few decades, the global demand for air conditioning is expected to skyrocket. According to the International Energy Agency, the number of AC units in buildings across the world should reach 5.6 billion by 2050, up from only around 2 billion units today. But unless air conditioning gets an efficiency revamp, all those ACs are going to put unprecedented strain on the electricity grid. Air conditioners and electric fans already account for approximately 10 percent of electricity consumption worldwide. On extremely hot days, AC efficiency drops, as the units have to work harder to move heat from indoors to outdoors. During a heat wave, millions of people come home and turn on their ACs at the same time, somewhere between the hours of 4 p.m. and 9 p.m. When that happens, air conditioning can account for a whopping 60 to 70 percent of electricity demand, and shake grids like California’s. Meanwhile, the key component of modern air conditioners — chemicals known as refrigerants — have been the bane of the atmosphere for decades. ACs work by exposing a liquid refrigerant, a chemical with a low boiling point, to hot indoor air. That heat causes the refrigerant to evaporate into gas, cooling the air. A compressor then turns the refrigerant back into liquid and repeats the process.
The problem is that refrigerants can leak out of air conditioners, both during use and, more commonly, when the ACs are discarded. Early ACs were largely made with chlorofluorocarbons, or CFCs, which were responsible for one of the first truly global climate anxieties: the hole in the ozone layer. CFCs were phased out by the 1987 Montreal Protocol, an international treaty to counteract ozone hole depletion, and eventually replaced by hydrofluorocarbons, or HFCs. But HFCs have their own problem — they are greenhouse gases that, in the short term, are thousands of times more potent than carbon dioxide. An amendment to the Montreal Protocol has HFCs set to phase down dramatically by the mid-2040s; in the meantime, however, they’re still contributing to global warming.
The next generation
There are a lot of ways to make existing AC technology more efficient.Some newer AC units use different refrigerants, such as one known as R-32, which has less planet-warming potential than other hydrofluorocarbons and also takes less energy to compress, thus saving electricity. Other units use technology known as “variable speed compressors,” that allow the unit to run on different settings. The compressor can speed up if it’s 100 degrees Fahrenheit and sweltering, or slow down if it’s only 85 degrees. That can help save on electricity and utility bills. And more advanced models are just around the corner. Kalanki was one of the leaders of an initiative at RMI known as the Global Cooling Prize, which rewarded manufacturers who could produce affordable AC prototypes that would be at least five times better for the climate than existing models. Two companies received the prize in tandem: Gree Electric Appliances and Daikin Industries. Both used traditional vapor compression technology but with improved refrigerants and clever designs that could change settings in response to outdoor temperatures.
Other companies, start-ups, and researchers are investigating whether they can ditch vapor compression entirely. A start-up called Blue Frontier uses a liquid that sucks moisture from the air and stores it in a tank to control the temperature. According to the company, this approach could save up to 60 percent of the electricity required to run an AC year-round. And a group of researchers at Harvard University has developed an air conditioning prototype that they call coldSNAP. The prototype doesn’t use a refrigerant, but uses a special coating on a ceramic frame to evaporate water to cool the indoor space without adding moisture to the air. “Because we don’t have the vapor compression system and the energy of trying to release and compress the refrigerants, the energy consumption of these systems is far, far lower,” said Jonathan Grinham, one of the researchers on the project.