COOLING | SHAPE MEMORY ALLOYS A moving core rather than a stationary heat exchanger avoids scaling The alloy core comprises stacks of SMA plates that are, typically, nickel and titanium of its modular nature the alloy stacks and balance of plant can be retrofitted into where the typical vapour compression loop would be in an HVAC system OToole says it can be scaled up to large-scale applications without loss of performance. Compressing the material rather than subjecting it to tension has allowed the team to run 70 million cycles, which is equivalent to 40 years of operation in a heat pump. Materials and efficiencies One of the technologys benefits is that there is a high commonality of components between systems, says OToole. The interchangeability of stacks means that, if I wanted to make a refrigeration or district heating system, I can take out the stack optimised for refrigeration and put in the heating stack. Of course, in refrigeration, well be running a slightly different heat transfer fluid, so its not as simple as just slotting things around. But the principle is that we can design something that looks very similar across the board, says OToole. The components, he says, are readily available; the company uses off-the-shelf hydraulic pumps, valves, steel and heat treatments. The materials for the alloys nickel and titanium are ubiquitous, adds OToole. Every electric vehicle in the world has nickel in the battery, and every golf club in the world has titanium its common stuff. Because the SMAs are not for medical purposes such as braces and prosthetics which is the technologys origins (see panel Origins) low-grade materials can be used, says OToole. And it doesnt matter if there are some surface nicks or inconsistent finishes because were not inducing a crack on the material, so its not going to fail, he says. A moving core rather than a stationary heat exchanger avoids scaling, and any build-up is blown off as the core moves and expands and contracts, says OToole. Because theyre non-reactive you could, in theory, put an additive into the fluids and flush it out as part of regular maintenance. We havent run our systems for five or 10 years in non-accelerated mode yet but, to date, we havent noticed any scaling because performance stays the same, he says. The perfect blend of the alloy core is a constant work in progress. As well as its Dublin-based large-scale test facility, Exergyn has a research laboratory in Prague, Czech Republic, where Dr Jan Pilch is tasked with researching the most effective element blends, stabilising them and making them operate at high performance for millions of cycles. Without this, OToole warns the performance starts to drop off after around 40,000 cycles, as gradual degradation destabilises the material into something commercially unviable. With the process weve developed between Jans work on the microstructure, and our work on the heat transfer and operation we can maintain less than 10-12% loss over millions of cycles. Its improving all the time; we have a ORIGINS SMA technology has its origins in biomedicine SMAs have been used for decades for dental braces and heart stents. into research because thats where the money was. 68 September 2021 www.cibsejournal.com CIBSE Sep 21 pp67-68, 70 Exergyn.indd 68 27/08/2021 13:43