Temperature exchange

A number of techniques have been used to increase this exchange, including active magnetic regenerative refrigeration (AMRR). The principle of this cycle uses a heat-transfer fluid – in contact with the magnetocaloric materials (MMC) – flowing from the cold side to the hot side when the MMC is heated (magnetised), and from the hot side to the cold side when the MMC is cooled down (demagnetised). This progressively increases the temperature difference between the cold and hot source to about 20K, making the system potentially suitable for commercial applications.

There are various potential applications. Initial developments have been orientated towards the commercial and domestic refrigeration markets, and include display cases, beverage coolers, and commercial or domestic fridges.

However, magnetic cooling can also be adapted to other refrigeration applications, such as air conditioning (including automotive), cryogenics or in heating systems – for example, heat pumps.

The demand is likely to be driven by environmental regulations, because magnetic heating or cooling does not use a refrigerant but, instead, a heating or cooling fluid, which could be water-based. As a result, there is no possibility of refrigerant leakage and no direct CO₂ emissions, so it fully complies with all regulations, including F-Gas in Europe and Environmental Protection Agency regulations in the US.

In addition, the magnetocaloric cycle frequency is typically between 1Hz and 3Hz, so the rotation speed of the machine is slow and, therefore, very quiet compared to traditional compression systems. According to recent research, MCE is predicted to have a significantly higher efficiency (coefficient of performance) than the present conventional methods, with the potential for a 30% energy saving.

Even though some products have come to market, there are still challenges that need to be addressed before there is large-scale deployment of the technology. The main issue is the supply of magnetocaloric materials, which are scarce. Reducing the material content, or identifying new materials, would increase viability.

According to magnetic refrigeration engineers Cooltech Applications, the fabrication process is not yet optimised and production costs are still high. Interface optimisations (for example, heat exchangers) between the devices and the equipment to be refrigerated also need to be modified for maximum efficiency. Finally, development of prototypes for various specific applications needs to take place.

Although there is a lot of academic work by scientists and engineers at universities and research institutions worldwide, the current market development is not fully mature. Some of the companies pushing the boundaries of this technology include Cooltech Applications and Nextpac, which is working on heat-pump applications.

In 2015, Cooltech Applications said it had produced a 150-700W product as part of a refrigeration system, and the first tests will be carried out at end users’ sites, such as supermarkets, this year.