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CLIMATE CONTROL SYSTEMS OF THE FUTURE

| 2013 |

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Harnessing the potential of thermoelastic technologyOngoing studies by a team at the University of Maryland are aiming to reduce greenhouse gas emissions and the production of CO2 via the use of novel thermoelastic technologies in cooling systems

OVER THE LAST 100 years or more, vapour-compression refrigeration technology has established itself as the most widespread and popular of the cooling methods available. Used extensively throughout public, domestic and industrial settings, the application of vapour-compression systems ranges from large public buildings to oil refineries, hospitals to the food industry and from hotels to natural gas processing plants. Whilst relatively cost-effective and efficient in its operations, the technology relies on a number of environmentally destructive substances. As governments and industries worldwide face growing pressure to make their operations more environmentally friendly, alternatives are being sought for the increasingly outdated vapour-compression based approaches to cooling.

Working towards a novel alternative to traditional methods, research within the Department of Materials Science and Engineering at the University of Maryland (UMD) is exploring the potential of groundbreaking thermoelastic cooling systems. Led by Dr Ichiro Takeuchi, previously a Fellow by Special Appointment of the Japan Science and Technology Agency, and currently Professor within the Department at UMD, the studies are expected to herald the advent of a more efficient, cost-effective and ecologically sound solution to current industrial and domestic cooling technologies.

A 1 TON AIR-CONDITIONING SYSTEM

Building on both the successes and problems experienced during previous collaborative projects, the team at UMD is currently pursuing the development of a 1 ton air-conditioning unit. “The platform for this research,” Takeuchi explains, “was laid through our recent work with Jun Cui at the Pacific Northwest National Laboratory (PNNL), one of the world’s foremost experts in shape memory alloys; Yiming Wu at UMD, whose hard work and insight have led us to successful prototype construction; and Reinhard Radermacher, the Director of the Center for Environmental Energy Engineering at UMD, whose decades of experience have always steered us in the right direction.” Following this work, Takeuchi has now shifted his attention to creating a larger cooling system, which will be the equivalent of a window unit air conditioner for residential use.

In pursuit of this aim, Takeuchi has assembled an exceptional team of collaborators, each of whom will be responsible for a distinct aspect of the project. The research staff at UMD will lead the work, focused on developing a new thermoelastic compression drive mechanism and heat exchangers, both of which are crucial to the technology’s success, whilst staff at the PNNL will look into materials optimisation and possible fatigue issues. At the same time, researchers at the United Technology Research Center (UTRC) in East Hartford, Connecticut, will focus their efforts on the systems end of the project.

Takeuchi and his collaborators are currently undertaking the construction of a demonstration unit for the 1 ton system, after which they will work together to carry out extensive testing of the prototype. Takeuchi has established an environment in which all involved parties offer critical feedback from a manufacturing point of view, with biweekly conference calls to maintain contact and productive communication between the researchers. “In developing this technology,” he summarises, “we will be able to achieve a clearer understanding both of the scalability of the technology and its ultimate commercialisation aspects.”

TENSION VERSUS COMPRESSION

In order for thermoelastic cooling to take place, it is necessary for some form of stress to be applied to the material, and Takeuchi’s previous experiments have explored the potential of subjecting the material involved to tension in order for this stress to be achieved. His studies in this direction were successful in confirming that the basic principle behind thermoelastic cooling is viable. However, they presented a number of challenges relating to the long-term durability of the materials involved, suggesting that fatigue may be a factor in limiting the technique’s potential applications. In order to alleviate this issue, the research team at UMD and PNNL are now working on a different method of stress application, in the form of compression. “Despite the fact that we are only four months into our new project we have already produced a number of ideas for implementing compression drives into the technologies we are developing,” Takeuchi enthuses. If the early signs that the administration of compression to a material does not cause fatigue prove valid, the group may well have opened up an exciting array of previously undiscovered avenues for future research, and

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potential applications for thermoelastic cooling techniques.

IMPROVING THE COEFFICIENT OF PERFORMANCE

Both traditional vapour-compression and novel thermoelastic technologies rely on the use of stress to induce phase transformation and the latent heat. Thermoelastic cooling systems such as those being pioneered by Takeuchi’s lab, however, use the latent heat absorbed or released during the solid-to-solid martensitic phase of transformation in order to pump heat. “Because of the high density of the refrigerant in thermoelastic cooling technologies,” Takeuchi elucidates, “a larger amount of thermal energy is stored in a given volume, giving our approach a higher efficiency than vapour-compression based methods.”

Indeed, the coefficient of performance of thermoelastic materials can be as high as 12.5 and because the refrigerant is stored in a solid state the technique is better for the environment than the use of vapour. This removes the need for chlorofluorocarbons, hydrofluorocarbons and hydrochlorofluorocarbons, all of which hold a high global warming potential (GWP). The researchers estimate that, given a full market penetration of thermoelastic cooling across the US, primary electricity consumption would be cut by 4.77 quads per year, reducing equivalent CO2 emissions by as much as 431 million metric tons by 2030.

MARYLAND ENERGY AND SENSOR TECHNOLOGIES

In order to exploit the full potential of the technologies they are developing, Takeuchi and his collaborators made the decision in 2009 to found a start-up company in order to lead the way for commercialisation of thermoelastic devices. Established as a Limited Liability Company (LLC), Mayland Energy and Sensor Technologies (MEST) is the sole licensee of thermoelastic technology within UMD and is based at the university’s Technology Advancement Building. “MEST is currently looking at several specific applications which

can be launched into the market in a relatively short period of time and has many exciting industrial contacts,” Takeuchi explains. Close collaboration is being developed between MEST and a number of potential partners, and the work is also complementary to the Department of Energy’s funded efforts within the university campus.

MEST is forming an invaluable bridge between the research underway at the university and the needs and requirements of current industry trends. In this way, the venture could prove to be the pivotal factor in thermoelastic technologies becoming sufficiently widespread to have a meaningful impact on global warming and the reduction of CO2 emissions.

THE BIGGER PICTURE

Thermoelectric technologies are not the only option for the inevitable replacement of vapour-compressing systems. There are several alternatives which are also based on solid state refrigerants, such as magnetocaloric cooling and electrocaloric cooling techniques. However, the researchers are confident that thermoelastic cooling will prove to be both the most cost-effective and efficient of the new generation of cooling systems available and that the technology can go on to achieve significant economic, environmental and social benefits via a huge array of eventual applications.

THERMOELASTIC COOLING

OBJECTIVES

To develop an energy efficient cooling system that eliminates the need for synthetic refrigerants that harm the environment. Thermoelastic cooling systems use a solid-state material – an elastic shape memory metal alloy – as a refrigerant and a solid-to-solid phase transformation to absorb or release heat. The aim of this research is to develop and test shape memory alloys, and a cooling device that alternately absorbs or creates heat in much the same way as a vapour compression system, but with significantly less energy and a smaller operational footprint.

KEY COLLABORATORS

Yiming Wu; Manfred Wuttig; Reinhard Radermacher; Yunho Hwang, University of Maryland, USA

Jun Cui, Pacific Northwest National Laboratory, USA

Thomas Radcliff, United Technologies Research Center, USA

FUNDING

Advanced Research Projects Agency-Energy (ARPA-E)

CONTACT

Professor Ichiro Takeuchi Principal Investigator

Department of Materials Science & Engineering Building 90 College Park Maryland 20742-2115 USA

T +1 301 405 6809 E takeuchi@umd.edu

www.takeuchi.umd.edu

www.energysensortech.com

http://link.aip.org/link/doi/10.1063/1.4746257

ICHIRO TAKEUCHI is Professor of Materials Science and Engineering and Affiliate Professor of Physics at the University of Maryland. Prior to joining the Maryland faculty, he was a postdoctoral researcher at Lawrence Berkeley National Laboratory. Takeuchi has also worked as a technical staff member at NEC Corporation’s Fundamental Research Laboratory in Japan. He obtained his BSc in Physics from California Institute of Technology and PhD in Physics from the University of Maryland. Takeuchi is a Fellow of the American Physical Society.

Takeuchi and colleagues have previously discovered fatigue-free thermoelastic materials using

combinatorial synthesis.

INTELLIGENCE

The group may well have opened

up an exciting array of previously

undiscovered avenues for future

research, and potential applications

for thermoelastic cooling

techniques

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Professor Ichiro Takeuchi is working to replace traditional vapour-compression cooling systems with more efficient alternatives. Here, he talks about the origins of this work and where it could eventually lead

What is thermoelastic cooling and how does it work? From where did this new technology emerge?

Themoleastic cooling is a novel solid state alternative cooling technology. We are working to eventually replace the ubiquitous vapour-compression based cooling systems. Vapour-compression systems have been around for a very long time and are efficient, but they use refrigerants which are harmful to the environment and have high global warming potentials (GWPs). Alternative solid state cooling technologies remove such refrigerants and make use of special solid materials to pump heat. We have been working with a class of materials called shape memory alloys which change their shapes upon application of heat. One day, we realised that the opposite effect must exist where, upon application of force to the alloy, it releases and absorbs heat. It turns out the effect is very strong and had not been explored for real applications, so we started carrying out demonstration experiments.

How does thermoelastic cooling differ from traditional methods? What are the main advantages/disadvantages?

Vapour-compression technology uses environmentally harmful chemicals which can leak into the air. Our thermoelastic cooling mechanism is entirely based on applying stress to solid alloys and thus does not affect the environment at all. Thermoelastic cooling devices would have long shelf lives and, according to our experiments, could be more efficient than vapour-compression devices. They can also be engineered to operate at any temperature, and are gravity independent, with no fluid leakage issues. One disadvantage is the material might have a limited number of cycles before we have to replace it; there are ways to mitigate the potential short fatigue life of the materials, and we are currently addressing them.

Thermoelastic cooling is mainly being designed for use in air conditioning and chillers. Are there any other potential applications?

Air conditioning alone can cover a wide range of applications. We are particularly interested in climate control systems for electric vehicles, where current systems substantially drain the overall electric capacity of cars. Refrigeration is another major application category and humidity control systems are another. We are also thinking about many simple consumer products: wine coolers, hand-cranked beverage coolers, small-scale refrigerators. On a lighter note, why not an exercise bike, where you crank the pedals to exercise and the bike, in turn, drives the stress-applying mechanical drive to cool you at the same time! Of course, because cooling is only half the operation cycle of this mechanism, we can also make a variety of heating systems using the latent heat.

Your team has already witnessed many achievements, including the development of a 35 W water-cooling system in 2011 and a 1 kW thermoelastic air-conditioner prototype in 2012. Could you reflect on these past accomplishments and discuss their impact?

Our seed project, funded by the Advanced Research Projects Agency-Energy (ARPA-E), was very successful. Because this technology was entirely new, we didn’t know what to expect or how it would turn out when we started making the prototypes. After the initial 35 W water cooler, we realised the heat loss in our prototype was largely undermining its performance and it was suggested that, in order to test the real viability of this technology, we should build a much larger scale system. This led us to the construction of the 1 kW air conditioner. A common residential window unit air conditioner is roughly 3.5 kW, so this gave us a good feel for what is involved in

upscaling our technology for real commercial applications. We encountered many little problems, but through identifying them we can piggyback on what we learned for our latest project, the 1 ton system.

Finally, do you have any plans to extend this research? What is the next step?

For now, we plan to closely follow the milestones chart we have set for the three-year ARPA-E project. Working with the ARPA-E Program Directors, we have laid out clear pathways to design, construct and test the 1 ton air-conditioning systems. With the new compression mode-based systems, we will first build smaller scale prototypes to see if the design ideas are sound and, once the problems are identified and solved, we can tackle the design and construction of the 1 ton system. Along the way, we also plan to draw up concrete plans for other applications and are in the process of filing new invention disclosures to add to our originally filed patent application.

The next generation of cooling systems

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