Solid-State Cooling Technologies Offer Alternatives to Traditional Air Conditioning
As global heat records continue to be set, the demand for air conditioning is projected to triple by 2050, raising environmental concerns despite its health benefits. Traditional AC units, while effective, contribute to global electricity use and greenhouse gas emissions. Scientists and startups are exploring solid-state cooling technologies, which move heat through conductive materials without refrigerants or complex moving parts. While these systems promise environmental advantages and durability, their efficiency compared to conventional AC remains a key question for researchers.
The International Energy Agency projects that the number of air conditioning (AC) units will triple by 2050. This surge in demand comes amid a period of record-breaking heat, with AC preventing an estimated 200,000 premature deaths in 2019, according to a Lancet study.
However, traditional AC units currently account for 7% of global electricity use and 3% of greenhouse gas emissions. Improper disposal can lead to refrigerant leaks, with some refrigerants like R410A having a global warming potential over 2,000 times that of carbon dioxide.
In response to these environmental challenges, researchers and startups are developing solid-state cooling technologies. Unlike traditional ACs, which use a compressor, a fan, and refrigerants to transfer heat, solid-state systems move heat through conductive materials such as gadolinium and bismuth telluride. These systems are currently used on a smaller scale in applications like mini-fridges, electric vehicle batteries, and high-end gaming computers.
Several pilot programs are underway. Brooklyn-based Mimic Systems is testing a room-scale thermoelectric cooling system, which passes a current through semiconductive materials, in a Vancouver apartment. The German company Magnotherm is trialing its magnetocaloric system, which transfers heat by magnetizing and demagnetizing materials, in supermarkets. A team in Hong Kong has developed an elastocaloric device that can achieve temperatures below 0 °C by expanding and contracting its material. The UK's Barocal is focusing on barocaloric systems that change temperature in response to pressure shifts.
Despite the promise, experts raise questions about efficiency. Pramod Reddy, a professor of mechanical engineering at the University of Michigan, highlights the challenge of matching the efficiency of typical thermodynamic cycles. Jeff Snyder, a professor at Northwestern University, notes that most modern HVAC systems have a coefficient of performance (COP) of 3, meaning they move three units of heat for every unit of energy. Thermoelectrics, in particular, tend to have lower performance for significant temperature changes, making them more suitable for niche applications.
Conversely, Lindsay Rasmussen, a manager at the Rocky Mountain Institute’s climate tech accelerator Third Derivative, suggests that efficiency is not the only factor. She points to the high global warming potential of refrigerants like R410A and the increased durability of mechanically simpler solid-state models. Mimic Systems claims its room-scale model could match the annual energy consumption of a typical AC unit. Room-scale prototypes for elastocaloric and barocaloric systems are anticipated within two to three years.
According to MIT Technology Review, more long-term energy consumption data is needed to fully compare the performance of solid-state alternatives with conventional models.
