26 March 2025
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Barocal’s latest TRL5 prototype is said to deliver cooling powers and temperature spans in line with vapour-compression systems while surpassing them in terms of energy efficiency
Solid refrigerants, or so-called ‘caloric materials’, have been proposed as a replacement for refrigerant gases for several decades. But so far, the underlying materials performance prohibited commercial applications. A research group from the University of Cambridge has now discovered a new class of materials which allow for ultra-efficient and low-cost use of solid materials called barocaloric materials. Florian Schabus, Chief Commercial Officer at Barocal, looks at why this is a potential game changer for the industry.
The first synthetic refrigerant gases were created in the 1920s and fundamentally changed cooling and refrigeration. The discovery of Freon allowed the industry to move away from toxic or flammable alternatives that would prevent widespread adoption. Refrigerant gases like CFCs or HFCs enabled the mainstreaming of comfort cooling and are the basis of our modern living standard. However, they cause severe environmental issues. Through the leakage of gases and low energy efficiency, the HVAC industry is contributing massively to climate change.
Given the size of the problem, numerous alternatives have been proposed, including the use of solid materials that undergo phase changes. The idea of using these so-called ‘caloric materials’ as a replacement for gaseous refrigerants to overcome their inherent challenges is not new. In fact, research into solid refrigerants has been going on for decades.
A history of unfulfilled promises
NASA first studied ‘magnetocaloric materials’ in the 70s and in the last decades many prototypes based on solid materials have been unveiled. Over the years scientists discovered different material classes that could be activated using e.g. magnetic fields, mechanical stress or electric fields. Contenders were numerous and the promise was usually the same: by replacing gases with solid refrigerants, one could eliminate the fugitive emissions associated with vapour-compression and increase energy efficiency. But none of this ever materialised.
The reason is simple: proposed systems were fundamentally limited by their core materials. The thermal performance of caloric materials at that time was by a factor of 100x lower than that of conventional refrigerant gases. A fight against intrinsic materials properties that even the best engineering cannot win. Plagued by low efficiency, low temperature lifts and high materials cost, the industry rightly saw this as largely an academic pursuit.
To have a realistic chance of competing against synthetic refrigerant gases, new refrigerants would have to fulfil several criteria: large entropy changes, low-cost base materials, simple activation mechanisms, long lifetimes - just to name a few. A seemingly impossible task for novel materials, keeping in mind that the vapour-compression industry had over 100 years to refine and optimise its technology.
The discovery of barocaloric materials
The University of Cambridge has been at the forefront of solid refrigerant research for the last 15 years and is the origin of seminal work in different areas of solid refrigerant research. Even the best existing solid materials only delivered temperature lifts of about 3°C under magnetic fields generated by permanent magnets, which is impractical for most real-world applications. The research group in Cambridge set out to change that.
A widely cited 2015 Nature Communications publication put so-called ‘barocaloric materials’ on the map. For the first time, Prof. Moya, who led the research group in Cambridge, found a solid material with the same thermal performance as conventional refrigerant gases. This was a huge scientific breakthrough.
Like refrigerant gases, these barocaloric materials go through a phase change when compressed and change their temperature based on changes in pressure. But it was not only their large entropy changes which triggered interest. Since these materials are organic, they are simple to produce and already available on a commercial scale. They don’t come with any environmental concerns and can be cycled almost infinitely while allowing for ultra-high efficiency operations. For the first time, there seemed to be a feasible pathway for new refrigerants to match conventional gases in terms of performance and cost while offering the potential of 2-3x higher energy efficiencies.
Pathway to commercial viability
However, it would take another few years for that materials promise to be proven in an actual system. Activating the materials takes high pressures and designing efficient heat transfer mechanisms proved to be difficult. The material can’t be pumped and the compressor and heat exchange design differ from existing systems. Barocal, a spin-out resulting from materials research at Cambridge, works on exactly that. Supported by the Global Cooling Prize, an initiative by the Rocky Mountain Institute and Breakthrough Energy, Bill Gates’ climate funding arm, it has been working on first functional prototypes based on these novel materials.
The Barocal team is working to develop systems around a new class of solid materials
With a team of 10 engineers and scientists, Barocal is working on new systems around these special materials. Their latest TRL5 prototype is said to deliver cooling powers and temperature spans in line with vapour-compression systems while surpassing them in terms of energy efficiency. The technology is modular and has a high energy density, making it suitable for most cooling, heating and refrigeration applications around ambient temperature.
This is a true paradigm shift for the scientific community, but to be a real contender to conventional cooling systems, the company will have to prove its ability to reduce the system cost to effectively compete with refrigerant gases on the market. Barocal plans to partner with OEMs and manufacturers to help achieve the scale and production volume necessary to reach cost parity, but a fundamental challenge remains: compressing a solid requires higher pressures than compressing a gas.
Outlook
The discovery of novel barocaloric materials may be foundational for an entirely new generation of refrigerants. The thermal performance of these materials matches that of refrigerant gases, and 1kg of materials can theoretically deliver over 121,000 joules. While research into new materials is ongoing, this performance already today is good enough for new cooling systems that have the same form factor and functional performance as conventional systems while offering 2x higher efficiency.
Amidst all the excitement, the real field proof is still out. The company plans to deliver the first field pilot systems later this year and will collect real deployment data together with OEMs. It remains to be seen whether this is the start of a real revolution or whether the market barriers are too big. After all, these systems would require different maintenance and are trying to change an industry that at times can be slow moving and largely cost-driven.
So 97 years after Thomas Midgley Jr. synthesized Freon, the first commercial chlorofluorocarbon, we may see another fundamental shift in refrigerants. And it is urgently needed. Without radical changes, refrigerant gas leakages will cause additional emissions of 57 Gt Co2e over the next 25 years. This is more than 1.5x the entire world’s annual emissions. Together with the energy efficiency savings, a switch to solid refrigerants could almost singlehandedly put us back on a 1.5°C pathway.
