Elastocaloric Heating and Cooling
A Sustainable Approach to Energy Efficiency
In the quest for environmentally friendly heating and cooling systems, universities and research laboratories are working on new, practical alternatives to traditional vapor compression systems. In this context, the use of caloric effects is gaining significance.
In most industrialized countries, the building sector is the largest energy consumer. In Europe, it accounts for 40 percent of total energy demand. In regions with cold winters, 75 percent of a building’s energy needs are for space heating. Due to global warming, increasing purchasing power, and improved indoor thermal comfort standards, the demand for cooling is also booming worldwide. The International Energy Agency (IEA) estimates that air conditioners currently account for almost 20 percent of total electricity consumption in buildings. By 2050, this share could triple.
The global demand for sustainable and energy-efficient heating and cooling systems is increasing, particularly with an eye on reducing CO2 emissions. Heat pumps are more environmentally friendly than many conventional heating systems. These efficient heating systems utilize environmental heat (e.g., from the air, water, or ground) to heat buildings.
Heat pumps operate on the principle of the thermodynamic cycle and can be used for both heating and cooling. They work similarly to a refrigerator, but in reverse.
The thermodynamic cycle process
- Evaporation: The liquid refrigerant absorbs heat from the surroundings and evaporates.
- Compression: The vapor is compressed in the compressor, increasing its temperature.
- Condensation: The hot vapor is passed through a heat exchanger, where it releases its heat to the heating system and condenses.
- Expansion: The refrigerant is directed through an expansion valve, reducing its pressure and temperature, and the cycle begins anew.
This technology is currently one of the best options for cost-effectively heating and cooling buildings. However, more efficient alternatives are being developed, especially since the refrigerants used in vapor compression heat pumps pose environmental problems. They are often flammable, explosive, toxic, or still significantly contribute to the greenhouse effect.
The elastocaloric heating and cooling process is based on a similarly simple principle as vapor compression heat pumps but does not require refrigerants. Instead, a shape memory alloy, usually a nickel-titanium alloy in the form of wires or sheets, is used. The elastocaloric material is stretched, causing a change in its internal structure and resulting in heating. This heat is transferred to the surrounding medium (e.g., air or water), warming it. When the material is subsequently unloaded, its temperature drops, allowing it to absorb heat from the surrounding medium. This absorbed heat can then be used for cooling. The heat pump employs a cyclic mechanism where the elastocaloric material is repeatedly stretched and relaxed.
Through these cyclic processes, heat is continuously absorbed from a cold reservoir and released to a warm reservoir, similar to the conventional refrigerant cycle in heat pumps. The generated heat is transferred to the heating system via a heat exchanger, while the extracted heat is transferred to the cooling medium using the same mechanism. The temperature difference is approximately 20 degrees Celsius.
Why are elastocaloric heating and cooling systems a better concept?
- The energy efficiency of elastocaloric systems is a key aspect. They can achieve high COP (Coefficient of Performance) values, which are 20 to 30 percent higher than those of conventional cooling and heat pump systems. The elastocaloric effect allows for the direct conversion of mechanical energy into thermal energy without the need for intermediate media such as gases or liquids used in conventional systems. This reduces energy losses and increases efficiency.
- Elastocaloric systems do not require refrigerants, eliminating the risk of emitting climate-damaging gases. There is no danger of leaks that could lead to health or safety issues.
- The materials used in elastocaloric systems, such as nickel-titanium alloys, are required in small quantities and have a long lifespan. They are highly recyclable, further reducing the ecological footprint.
- Elastocaloric air conditioning units could be used in both residential and commercial buildings.
Thanks to the smaller size and lighter weight of elastocaloric modules, more compact and lighter devices could be developed. - Household appliances could benefit from this technology by providing consistent cooling
without the use of chemical refrigerants. In industry, elastocaloric systems could be used for cooling processes and machinery, reducing energy consumption and increasing sustainability.
The World Economic Forum (WEF) has included elastocaloric heating and cooling technology in its “Top Ten Technologies 2024.” Research and development in this area are advancing rapidly, with the number of scientific publications doubling every 22 months. The increase in patent applications underscores the growing commercial interest in this technology.
On the technological side, materials and device design have been continuously improved; new prototypes demonstrate the capabilities of elastocaloric heat pumps. Universities and companies have developed several functional prototypes, experimenting with the use of complementary materials and innovative production techniques. As a layperson, one might hope that production could begin soon.
Recently, the research project “SMACool” at Saarland University made headlines. The new elastocaloric heat pump technology allows buildings to be heated and cooled through ventilation slots alone. The project’s goal is to develop a decentralized air conditioning system within three years, capable of individually heating and cooling separate rooms.
Professor Paul Motzki, who leads the SMACool project consortium, explains: “We aim to heat and cool houses not with a central system, but in a decentralized and individualized manner for each room. We are developing a compact unit that contains our technology and can be integrated directly with the required ventilation system in new houses.”
Innovative ideas like these can provide alternatives to conventional heating and cooling methods, significantly reducing energy consumption and having less impact on the climate and environment. Unfortunately, Viessmann has sold its heat pump division, but Bosch is now seeking to better position itself globally in the field of heat pumps and air conditioning devices through acquisitions. It is not only about leading in research; such innovative systems must also be brought into production.
Doris Höflich, Market Intelligence Senior Expert
Sources:
- Universität des Saarlandes, 02.04.2024
- Clean Technika, 22.07.2024
- Fraunhofer IPM
- World Economic Forum
- Bild-Quelle: Fraunhofer IPM: Elastocaloric Systems
