Shape-memory alloy could replace HFCs

A small company in Ireland has developed a new type of air conditioning system that could negate the need for hydrofluorocarbons (HFCs).

Researchers at Exergyn, based in Dublin, worked in secret collaboration with another company – believed to be Carrier – for two years on the project. The system uses a shape-memory alloy (SMA) called nitinol, which is a blend of nickel and titanium. SMAs are alloys that can be deformed in low temperatures, but return to their original shape when heated.

In the original prototype, the company created plates of the alloy with holes to allow heat-carrying liquids or gases through. The plates are assembled into stacks, which are each compressed in sequence by hydraulic rams or electric actuators.

Exergyn’s Managing Director Dr Kevin O’Toole says the team has been operating a 60kW heat pump for the past two months at its test facility in Dublin without any issues. There are plans for the unit to be shipped to a HVAC&R partner facility for continued testing in a month or so.

“We are continuing to develop new blends of shape-memory alloy which offer further advantages – such as higher material efficiency or lower operational loading requirements,” says O’Toole.

“The 60kW unit comprises our α-blend, with a material coefficient of performance, COPmat – measured as the cooling capacity of the material divided by the work input required to drive the thermodynamic cycle at the material level – of just over 20. Our β blend is now almost ready to go, which is 20 per cent more efficient providing a COPmat of 25. Due to the inherent interchangeability of the SMA in the system, this is expected to translate directly into a 20 per cent increase in system efficiency compared to current performance. A COPmat of 25 is on par with R134a – the world’s most common refrigerant gas.”

Exergyn is exploring other options in the HVAC&R industry where nitinol can be used, including in refrigeration, air conditioning and district heating. O’Toole says there are areas in the sector where current systems are either very complex or come at high production costs, and has identified this as a market where the technology can be utilised.

It is estimated that using SMAs will be approximately 30–40 per cent cheaper to run than traditional systems. The materials are also cheaper to buy, lighter and smaller, and testing has indicated the units could last for more than 40 years.

Exergyn is looking into automotive cooling (specifically for electric vehicles), and has had some initial discussions about aerospace applications.

O’Toole has also seen possibilities in the system being used to recover energy from low-temperature heat sources. However, he says his interest initial interest in SMA was not environmentally driven, but rather interest-driven.

“My initial work with the material was in the field of robotics and smart prosthetics in the mid-2000s,” he says.

He and a colleague noticed that there seemed to be a range of potential applications in the energy space for which the properties of SMA would be ideal.

“The realisation that SMA could be the answer to the HFC issue arose over time as we started to see through our work just how effective it is in heat pump applications.”

Exergyn has been conducting early trials of the product, but O’Toole says there is more work to do before it can hit the market.

“Exergyn’s business model is to take the technology to a ‘field-trial ready’ state,” he explains. “Thereafter we depend on large manufacturing partners to work with us to ‘productionise’ the system.”

It is expected customer trials will occur in a couple of years, with early low-volume production to begin in three or four years.

Exergyn is supported by equity investment and grants from Enterprise Ireland, SEAI, EU Horizon 2020, Carbon Trust UK and the Irish Government’s Disruptive Technologies Innovation Fund.

Image courtesy of Exergyn.

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