A cooling system with no moving parts or environmentally damaging refrigerant liquids or gases can work almost twice as efficiently as a standard air-conditioning system, which could slash electricity use.
Most air conditioners and fridges rely on compressing and expanding a fluid to either absorb or release large quantities of heat. While these systems are relatively cheap and simple to produce, they aren’t very efficient and so require lots of energy – about a fifth of the electricity used in buildings globally – and many of the coolants used are environmentally harmful.
Now, Emmanuel Defay at the Luxembourg Institute of Science and Technology and his colleagues have developed a coolant-free refrigeration device made from the metals lead, scandium and tantalum. It can reach maximum efficiencies of more than 60 per cent, almost double that of typical single-room air conditioning units.
The technology relies on a principle called electrocaloric cooling, which is when an electric field applied across a material changes the direction of electric charges, causing a temporary increase in temperature and a subsequent decrease when the electric field is removed.
To make their cooling system, Defay and his colleagues stacked eight strips of the material known as lead scandium tantalate, which is electrocaloric, on top of one another and immersed them in a heat-carrying fluid, silicone oil. When an electric field is switched on and the strips heat up, the fluid moves to the right, and when it cools down, it moves to the left, creating permanent regions of hot and cold of about 20°C difference.
These regions can be used as hot and cold reservoirs from which the oil can be circulated through pipes to cool or heat rooms or objects as desired.
Although the efficiency of the device is theoretically 67 per cent, the current design is around 12 per cent efficient. This could be improved if a better conductor of heat than the lead scandium tantalate were found, says Defay.
“A superlative performance has been achieved by combining known elements,” says Neil Mathur at the University of Cambridge. Using thin strips of electrocaloric material instead of one lump of material means that high electric fields can be applied without the material breaking down, giving a better cooling performance, he says. However, he adds, the team only looked at the cooling power of the stack of metal strips themselves, whereas it would be interesting to see how the entire device performs together.
- energy and fuels/
- materials science