To address global climate and energy challenges, more efficient and environmentally friendly alternatives to current cooling and heating systems in air conditioning need to be explored. The emerging technology of "elastocalorics" has been recognized by both the EU Commission and the U.S. Department of Energy as the most promising alternative to today's typical vapor compression processes, such as those used in refrigerators, air conditioners or heat pumps. Current methods have many drawbacks, including the use of environmentally harmful refrigerants that contribute to global warming. Even carbon-based refrigerants have undesirable properties such as flammability. At the same time, such systems are very energy-intensive to operate. The most efficient systems achieve a coefficient of performance (COP) of 5-6, which means that 1 kW of electrical energy produces only 5-6 kW of thermal energy. It is therefore crucial that research and development in the field of elastocalorics is promoted in order to realize sustainable and energy-efficient solutions.

These efficiencies can be increased many times over by using elastocaloric systems. New elastocaloric materials have COPs in excess of 30 (i.e., 1 W of input power produces 30 W of heating or cooling power), and current technology demonstrators achieve efficiencies in excess of 9. Depending on the application, elastocaloric systems can be used as heat pumps or cooling units - or both. There is no need to use harmful refrigerants and the contribution to global warming is estimated to be zero.

Top row of images: When the superelastic shape memory element changes length, it undergoes a significant temperature change that can be used to transport heat.

Principle of elastocalorics

Similar to a camshaft, the SMA bundles are stretched as they move up a ramp and relieved as they move down, absorbing and releasing heat as they rotate.

Nickel-titanium alloys, commonly referred to as shape memory alloys (SMAs) and belonging to the class of smart materials, are used in a wide variety of industries. More and more examples of applications of so-called shape memory actuators are being presented and introduced to the market. These smart materials are also becoming increasingly important for elastocaloric applications. Originally developed for medical applications (e.g. stents, braces and "indestructible" glasses), the superelastic variant of the alloy undergoes a phase transformation under mechanical stress. This transformation causes a change in the energy content of the material, resulting in the release or absorption of heat. The so-called latent heat generated or required during these transformations is a crucial material parameter for the development of elastocaloric systems.

Recent research in the field of materials has shown promising results for elastocaloric applications. With optimized materials, temperature changes of up to +/- 30 degrees and material COPs of up to 30 have been achieved on a laboratory scale. The next step is to translate these results into suitable concepts and to develop energy-efficient elastocaloric units. Further progress in systems research is aimed at maximizing the COP and exploring the potential for practical applications.

Machine concepts

The Smart Materials Systems group at Saarland University has developed the world's first continuous air-to-air demonstrator for elastocalorics. In the realized concept, wire bundles are used to generate temperature changes and cooling power. This design provides 20 degrees of temperature change and 250 W of cooling power with only 50 g of nickel-titanium material. The specific power of the system is 5 kW/kg, which can be significantly increased by future scaling and cascading.

The first system demonstrators have shown the potential and feasibility of elastocaloric technology.

Prof. Dr.-Ing. Paul Motzki

The design of elastocaloric systems offers advantages such as the direct use of air as a coolant, which eliminates the need for heat exchangers and simplifies the system. In addition, both air and water cooled systems are possible, and the thermal performance of the systems can be adapted to the requirements of the application through appropriate heat transfer. The inherent sensor technology based on super-elastic shape memory alloys also provides the ability to monitor the condition of the system, enabling predictive maintenance and making the control system intelligent.

Elastocalorics can be used in a wide range of applications, such as air conditioning in buildings, household appliances, industry, data centers and automobiles. In the field of life sciences, there are already industrial projects for the use of elastocaloric units in analytical devices. In addition, the technology is being further developed and adapted along the entire value chain, with a focus on materials research and the development of intelligent overall systems with low energy requirements. The modular and scalable design of the elastocaloric systems allows them to be adapted to different applications, from wine coolers to storage climate control.

Although elastocaloric technology is still in its infancy, interest in environmentally friendly air conditioning alternatives is growing. Ongoing projects continue to develop the technology and find new applications. Due to their energy efficiency and adaptability, elastocaloric systems have the potential to revolutionize air conditioning in several areas.