'Electrocaloric' material could lead to more efficient refrigerators

A team at the National Physical Laboratory (NPL) is trying to develop the first practical ‘electrocaloric’ cooler, providing much greater efficiencies than conventional gas-based refrigeration systems and without the high costs of using large magnets to generate low temperatures.

The NPL engineers are hoping to take advantage of a breakthrough made in 2006 when scientists showed the electrocaloric effect, which causes materials to change temperature under an applied electric field, was much larger in thin film substances than in bulk solids and big enough for its use in cooling applications.

‘It is has taken us until now to develop the understanding to take this to a stage where we can develop a real cooler, but we believe we are now at that stage,’ lead researcher Tatiana Correia told The Engineer by email.

Typical domestic fridges use a continuous cycle of vapour compression and expansion of chemicals such as Freon that condense into liquid and absorb heat from the surroundings. These chemicals can be harmful to the environment and such systems have fairly low efficiencies of around 30 per cent.

Other cooling systems apply magnetic fields to provoke a cooling effect in materials but these require large, expensive equipment. Applying a voltage to a material creates a temperature difference across it but this has a very low inherent efficiency of around 10 per cent.

By contrast, theoretical predictions put the efficiency of electrocaloric at 60 to 70 per cent – comparable with magnetic cooling but potentially achievable with much smaller and cheaper equipment.

‘An electrocaloric cooler could potentially deliver higher efficiency than vapour compression as the creation of an electric field requires less energy than the compression process to create the same level of cooling,’ said Maciej Rokosz, a PhD student at NPL and Imperial College London.

Correia declined to say what methods or materials NPL planned to use to develop the cooler but that the team would be assessing a range of designs.

‘We are confident that our design ideas, combined with the expertise we have at NPL and Imperial, will be able to develop a viable cooler,’ she said. ‘However we are still very keen to hear from industry who can work with us to look at the different applications this could be applied to.’

NPL is also developing and leading a new multimillion pound project funded by European Metrology Research Programme entitled METCO (Metrology of Electro-Thermal Coupling), bringing together academia and industry to develop capabilities for the traceable and accurate measurements of electrocaloric effect in materials.