The overall contribution of the refrigeration sector to climate change is frequently overlooked and according to the IEA in 2018 “Growing demand for air conditioners is one of the most critical blind spots in today’s energy debate”. Looking at the identified nine selected key technologies (EU commission, 2020), cooling again is not listed. The trajectory of cooling is changing dramatically BUT is not on the agenda. Approximately 10% of total greenhouse gas emissions stem from cooling alone, 20% of the global electricity is used. Roughly 3 billion cooling devices are used for household, commercial and transport refrigeration, air conditioning and heat pumping and the amount in increasing rapidly. Facing this development, it becomes clear that our current cooling technology based on vapour compression cycles needs to be changed.
New solid-state based cooling technologies provide higher energy efficiencies using materials with a phase transition, for which a driving stimulus such as magnetic field, electric field or pressure is applied. During this process the material can heat up or cool down, when exposed by a magnetic field, this is called the magnetocaloric effect (MCE).
Solid refrigerants are non-explosive, non-toxic and easier to recycle. However, the problem of today's magnetocaloric refrigerants is that the largest effects are shown by materials with first-order phase transitions. While they exhibit significant changes in temperature, their inherent hysteresis gives rise to irreversibility and energy losses during cyclic operation hindering full exploitation of the material’s caloric potential.
Magnetocaloric refrigeration has struggled to break into mass markets because it is a relatively expensive technology resulting from the large volume of high-performance permanent magnets required for this technology. Cool Innov rethinks the whole concept of the conventional caloric cooling. Instead of trying to squeeze the best out of magnetocaloric materials in relatively low magnetic fields, we introduce a second stimulus in the form of mechanical load. This allows a significantly improved exploitation of the material’s caloric potential and a reduction of the permanent magnet volume at the same time. A comparison between the conventional and multi-stimuli solid-state cooling cycle is shown in Fig. 1.
One important objective of Cool Innov is the development of existing and discovery of new refrigerant materials that show caloric effects both under the magnetic field and under mechanical load, requiring high magneto- AND elastocaloric response under ideally small stimuli. Consequently, the material needs to be mechanically and chemically stable and composed of non-resource-critical elements.
The next objective is the shaping of the materials into geometry that will allow the most efficient heat exchange during the operation of the thermodynamic cooling cycle, which we tackled by using the concept of additive manufacturing.
Finally, combining our breakthroughs in material physics & science with advanced engineering and processing, we built a worldwide unique testbed that allows the validation of multi-caloric materials in a multi-stimuli cooling cycle.
