Crystal-based cooling could make fridges more sustainable

A new type of crystal could enable refrigerators and air conditioners to keep us cool without warming the planet.

Refrigerators and air conditioners get their cooling power by circulating a liquid through the device, which absorbs heat and causes chilling through a cycle of evaporation and condensation. But many such liquids contribute to the greenhouse effect, causing further warming when they leak. Now, Jenny Pringle at Deakin University in Australia and her colleagues have made a climate-friendly alternative to these liquids using “plastic crystals” – crystals with molecules that can move just enough to make them pliable.

Under enough pressure, these plastic crystals can transform. Their molecules go from being randomly oriented to aligning themselves into a neat grid. Then, when pressure is removed, they become disordered again. As part of this disordering process, the crystals absorb heat, effectively cooling their surroundings.

Such pressure-based cooling has been investigated before, but most materials capable of this transition could only do so at balmy temperatures, limiting their cooling power, says Pringle. In contrast, the heat-sucking ability of her team’s crystals kicks in at temperatures from -37°C (-34.6°F) to 10°C (50°F), a suitable range for household refrigerators and freezers.

However, the new crystals are not ready to leave the lab yet. That’s because the pressures needed to make them work are very high – hundreds of times greater than atmospheric pressure and equivalent to being thousands of metres underwater, says Pringle.

David Boldrin at the University of Glasgow, UK, says materials like those in the new study have “the potential to almost completely decarbonise this huge [cooling] industry”, but he shares the concern about the high pressures required.

There may be another practical issue with this approach, says Bing Li at the Chinese Academy of Sciences. With every repeated use, each crystal may absorb less heat, as the grid the molecules form becomes more strained. Still, Li is optimistic and says he is confident the technology could be applied in the “near future”.