Barocaloric solid-state cooling: from materials to devices

The world is currently trapped in a vicious heating cycle, whereby global warming increases the need for cooling technologies, but these technologies themselves exacerbate global warming. Vapour-compression refrigeration, the method that currently dominates, relies on gaseous refrigerants that contribute significantly to global warming and accumulative “forever chemicals”. For this reason, there is a widely acknowledged, urgent need to find a successor technology. Among the most promising such technologies are heat pumps based on barocaloric materials. Like vapour-compression refrigerants, these materials can be converted between high- and low-entropy phases by applying external pressure; the crucial distinction is that here both phases are solid, so that they cannot leak to the atmosphere. This enables clean, compact, and efficient refrigeration. In our previous EPSRC-funded work, we have developed an unprecedented understanding of the atomic structure and dynamics that give rise to barocaloric effects. As a result, we have developed several novel, highly promising materials. However, there is a limit to what can be learned from laboratory measurements on the materials alone. For instance, the thermal conductivity, which limits the cooling power, depends not just on the barocaloric material but on the whole device architecture, while the device efficiency is crucial to real-world competitiveness; both of these require a full working model to determine accurately. To progress further, we therefore need to build and test a working prototype, which will bridge the gap between academic materials research and future commercial development. This is precisely what we propose here. We will produce a working demonstrator model whose design and components can easily be tuned, and use our expertise in the physics and chemistry of barocaloric materials and heat transfer engineering to optimise its properties. In particular, we will use experience from other caloric materials to incorporate active regeneration, which will allow this device to operate over a larger, and hence more useful, temperature drop. At the conclusion of this project, the prototype will be sufficiently competitive with existing cooling systems to achieve early-stage financing towards further development. Achieving barocaloric refrigeration on a commercial and industrial scale will remove our dependence on fluorinated refrigerant gases, thus reducing their contribution to global warming (typical global warming potentials are over 1000 times that of CO2 by mass) and environmental accumulation. Because of this technology’s high efficiency, it will also reduce the power consumption associated with heating and cooling. Widespread use in the UK and worldwide (global market size US$233B; projected annual growth 6–7%) will have a very substantial economic impact.