As climate change pushes temperatures higher around the world, demand for air conditioning is rising rapidly.
The International Energy Agency (IEA) estimates that energy demand for space cooling could more than triple by 2050, driven largely by the rapid spread of air conditioning.
But these cooling systems are a significant climate problem of their own.
Cooling’s climate cost
Most cooling technology in use relies on vapor-compression technology, which circulates chemical refrigerants through a compressor. “The cooling sector has historically been very risk-averse,” said Berardo Matalucci, co-founder and CEO of MIMiC Systems, a Brooklyn-based company building alternative cooling technology that replaces bulky compressor units for hotels, offices and homes. “Almost every air conditioner is on 19th-century innovations.”
Jarad Mason, an associate professor of chemistry and chemical biology at Harvard University, who studies solid refrigerants for cooling systems, explained that “pretty much every air conditioner, refrigerator and heat pump that you use in the US has a vapor compression system that uses a fluorocarbon-based refrigerant.”
Those refrigerants, also known as hydrofluorocarbons, are potent greenhouse gases, “orders of magnitude (stronger) than carbon dioxide,” Mason said.
Greenhouse gases warm the planet by trapping heat that would otherwise escape into space, and even small leaks of refrigerants from air conditioners can have an outsized climate impact.
Even though these cooling systems are designed as closed loops, refrigerant leakage is widespread.
“It’s not practical at scale to make these systems leak-free, and still cheap enough to be commercially viable,” Mason said.
According to Mason, refrigerant gases, including fluorocarbon gases used in refrigerators and heat pumps, contribute around 2% to 3% of global greenhouse gas emissions, approaching the climate impact of the entire aviation industry.
Matalucci adds that, “as refrigerant escapes into the atmosphere, it also causes a lack of efficiency. So (appliances) draw more and more electricity.”
Bringing new technology into homes
According to Mason, solid-state cooling systems were developed in the middle of the 20th century but have historically been confined to niche applications like portable coolers, spacecrafts and submarines, where reliability and safety are leading priorities.
“One would be hard-pressed to find a solid-state device that’s being used at scale for air conditioning,” Mason said. Not only are solid-state devices more expensive, “one of the biggest challenges is reaching an energy efficiency, or coefficient of performance, that is comparable to existing systems,” he said.
According to data from the nonprofit, global energy systems think tank Rocky Mountain Institute, conventional air conditioners typically operate at an average coefficient of performance (COP) between two and four, with the most efficient systems reaching around five or six under optimal conditions. By contrast, solid-state cooling devices have demonstrated a wide range of COPs from below one to well above 10. Matalucci and Mason agree that most solid-state systems have yet to match the efficiencies of conventional air conditioners.
