Science to the rescue: Environmentally friendly refrigerants and safe ways to dispose of the harmful ones

Researchers are developing new, environmentally friendly refrigerants and finding more ways to recycle or break down harmful ones as the need to mitigate the potential of ecological harm from rapidly growing global demand for air-conditioning and refrigeration technologies becomes increasingly urgent.

HKUST: Engineers Set New Benchmarks in Eco-Friendly Cooling Technology

Engineers at the Hong Kong University of Science and Technology (HKUST) have developed an innovative elastocaloric device that boasts a temperature lift of 75K but also enhances efficiency by an impressive 48 per cent, all while utilising sustainable materials.

In contrast to refrigerant-based systems, elastocaloric cooling technology leverages the latent heat from shape memory alloys (SMAs), offering a promising and eco-friendly alternative.

These SMA refrigerants are greenhouse gas-free, completely recyclable, and energy-efficient, presenting a clear advantage over conventional cooling methods.

Previous elastocaloric devices faced limitations due to their modest temperature lifts, ranging from 20K to 50K. This performance metric is crucial for the device’s ability to transfer heat effectively from a lower temperature area to a higher one, which is vital for broader commercialisation. 

To tackle these challenges, Professors Sun Qingping and Yao Shuhuai from HKUST’s Department of Mechanical and Aerospace Engineering led a research team to create a multi-material cascading elastocaloric cooling device using nickel-titanium (NiTi) shape memory alloys.

By selecting three different NiTi alloys that operate at varying phase transition temperatures, the team effectively matched the operating conditions of each unit with its optimal temperature range.

This approach expanded the cooling device’s superelastic temperature window to over 100K, leading to a significant increase in cooling efficiency. The device achieved a temperature lift of 75K on the water side, breaking the previous world record of 50.6K.

The research team’s achievements in elastocaloric cooling technology have generated significant interest. Next, they aim to further refine their high-performance shape memory alloys and develop devices tailored for sub-zero cooling and high-temperature heat pump applications.

“With the continuous advancement of materials science and mechanical engineering, we are confident that elastocaloric refrigeration can provide next-generation green and energy-efficient cooling and heating solutions to feed the huge worldwide refrigeration market, addressing the urgent task of decarbonisation and global warming mitigation,” said Professor Sun.

With space heating and cooling predicted to account for 20 per cent of the world’s electricity consumption, and expected to become the second-largest contributor to global electricity demand by 2050, the implications of this research are profound. 

Red Mud: A Green Catalyst for R134a Decomposition

A team at the Korea Institute of Energy Research (KIER) has developed a revolutionary catalyst made from ‘red mud’, a byproduct of aluminium production. This catalyst effectively decomposes R134a – one of the world’s most-used refrigerants – turning a major industrial waste product into a powerful tool for fighting climate change.

Research leader Shin-Kun Ryi described red mud as “a strongly alkaline substance that can cause severe environmental pollution if it enters the surrounding environment” and explained that until now “there have been no suitable technologies to process and recycle it”. 

“The developed catalyst manufacturing technology not only recycles waste to reduce environmental pollution but also effectively decomposes refrigerants, which have a strong greenhouse gas effect, with excellent performance.” 

The production of 1 tonne of aluminium yields 1.5 tonnes of red mud, a reddish-brown residue containing oxides of iron, aluminium, silicon, and other elements. This waste material, generated at a rate of more than 180,000 tonnes annually, often ends up in landfills or is dumped into lakes, leading to soil and water contamination. 

R134a is most commonly destroyed through combustion and plasma methods, both of which have their drawbacks. 

Combustion generates secondary pollutants, while plasma decomposition requires significant energy and high equipment costs.

KIER’s innovation lies in repurposing red mud, a material composed of more than 50 per cent iron and aluminium, making it an effective catalyst for decomposing R134a because its porous structure and thermal stability allow for efficient reactions and prevent catalyst degradation.

The team also enhanced the decomposition process by employing a simple heat treatment that induced interactions among calcium, silicon, and aluminium components within the catalyst, resulting in the formation of a composite material composed of tricalcium aluminate and gehlenite, which strengthens the catalyst particles and increased their surface area, improving their overall efficiency.

Hydrogen fluoride produced during the decomposition of R134a reacts with calcium oxide present in the catalyst, forming calcium fluoride, a stable compound that coats the catalyst surface, preventing its deactivation.

By achieving a 99 per cent decomposition rate and suitability for mass production, KIER’s red mud discovery looks promisingly effective for reducing greenhouse gas emissions while promoting a circular economy and providing a solution to the environmental challenges posed by red mud and R134a.

EARTH: $26m to Reclaim, Reuse, Replace Refrigerants

The University of Kansas (KU) has been awarded a $26 million grant from the National Science Foundation to establish the Environmentally Applied Refrigerant Technology Hub (EARTH), which will tackle environmental challenges posed by heating, ventilation and air-conditioning. 

After five years, EARTH could become even bigger if the renewal option is successful, meaning this ambitious initiative could last up to 10 years with a $52m budget.

EARTH director Mark Shiflett said the program will “develop sustainable, accessible, and equitable refrigerant technologies and practices through research, education, and innovation that will improve quality of life and combat climate change”.

As HFCs leak from systems over time, they contribute 7.8 per cent of total greenhouse gas emissions. The American Innovation and Manufacturing (AIM) Act, passed in 2020, aims to phase out HFC production and use in the United States over the next two decades, which is a critical step in climate change mitigation.

However, significant challenges remain, including the lack of readily available, environmentally friendly alternatives for some applications and a shortage of skilled workers to implement new technologies. 

“There is a tremendous need to develop cooling and heating technologies that use less energy and new refrigerants that are safe for the environment,” said Mary Rezac, dean of the KU School of Engineering.

“EARTH will be a critical national resource to address these challenges.”

Through a multidisciplinary approach, EARTH brings together researchers from 80 institutions nationwide, including the University of Notre Dame, Maryland, Hawaii, South Dakota, and Lehigh University.

The project focuses on three key research areas: developing efficient methods to reclaim and reuse refrigerants, minimising waste and reducing reliance on new production; creating new, safe, and environmentally friendly refrigerants with low global warming potential (GWP), offering viable replacements for current high-GWP options; and improving the energy efficiency of HVACR systems, leading to further emissions reduction and a decrease in overall energy consumption.

“Working closely with industry partners, EARTH will have the resources and expertise to solve the technical, environmental, and economic challenges required to create a sustainable refrigerant lifecycle that will benefit Kansans, the nation, and the world,” said KU chancellor Douglas Girod.