Conventional cooling technology relies on gas compression, which involves a phase transition of the refrigerant from a liquid to a gas and back again, driven by changes in the pressure applied. Travelling through a series of coils and tubes that make up the condenser and evaporator, the liquid absorbs the heat inside the fridge, effectively cooling it down. It then turns into a gas again, and the cycle starts anew.

The problem: conventional fridges use hydrofluorocarbons (HFCs) as refrigerants, which are known greenhouse gases and could account for up to 45% of projected CO₂ equivalent emissions by 2050. In addition, gas compressor systems are not particularly efficient – at least compared to magnetic cooling, which has the potential to reduce the electricity consumption of a domestic fridge by 50%, says the academia-industry team that worked on the SSEEC project.

Cool... as a magnet

“We were looking at phase transition materials that remain in a solid state,” explains project coordinator Karl Sandeman of Imperial College London. “By applying a magnetic field, we change their magnetic property and they release or take in heat, depending on whether the field is being applied or removed. So, the magnetic cooling cycle is analogous to the conventional gas-compression cycle, only that instead of pressurising and de-pressurising, you magnetise and de-magnetise.”

Looking at the temperature range and power requirements, this technology works particularly well for a system the size of a domestic fridge, but is not as well suited to a heat pump in a heating, ventilating, and air conditioning system, for instance, SSEEC found.

Substantial CO₂ savings

Currently the total electricity consumption of the domestic fridge is about 5-6% of Europe's total electricity production. This translates into significant CO₂ savings. In addition, the adoption of magnetic cooling would significantly cut greenhouse gas emissions because of the solid nature of the refrigerant.

But before this will be possible, a lot of work is needed to further refine the technology. The SSEEC project has already made some headway. Among the greatest challenges were the refrigerants, their synthesis and shaping.

Previously, refrigerants for magnetic cooling had almost always used gadolinium, a relatively rare and thus expensive metal. The SSEEC team developed low cost refrigerants, which nonetheless provide substantial cooling power. The next step was to find a way to shape and cut thin plates of these refrigerants without compromising their structure – not an easy feat, since they go through a phase transformation at room temperature.

DRREAM of magnetic cooling

Building on these and many other SSEEC achievements, many of the project partners went on to a new EU-funded project called DRREAM, which continues to press ahead with magnetic cooling technology.

“Your fridge typically lasts 10 to 15 years, so for appliance manufacturers, reliability is a key element,” says Neil Wilson of Camfridge, one of the SME partners from SSEEC and now in DRREAM. “Tied to that are of course your manufacturing processes, which also drive your costs. If you can start to use standard processes that are automated, you are going to get standardised parts, so you can improve reliability. At the same time, by developing those processes, we can also demonstrate that our costs are in line with what the manufacturers are looking for.”

According to Wilson, initial appliances could become available within two to three years, followed by mass market availability in the subsequent two or three years.