Thermoelastic Active Regenerators with Giant DeltaT

Lead Performer: University of Maryland – College Park, MD
Partner: Maryland Energy & Sensor Technologies, LLC (MEST) - College Park, MD
DOE Total Funding: $1,800,000
Cost Share: $450,000
Project Term: April 1, 2020 – March 31, 2023
Funding Type: Buildings Energy Efficiency Frontiers & Innovation Technologies (BENEFIT) 2019

Project Objective

Thermoelastic (also called elastocaloric) cooling is one of the most promising alternative cooling technologies. It employs latent heat of martensitic transformation in metal to pump heat. Owing to the high latent heat to the input work ratio, the coefficient of performance (COP) of a thermoelastic material can be as high as 80% of the Carnot limit. This high materials COP is only rivaled by magnetocaloric materials. The University of Maryland, in partnership with Maryland Energy & Sensor Technologies, LLC (MEST), will demonstrate for the first time thermoelastic active regenerators with hitherto unattainable system deltaT using active regeneration schemes implemented to increase temperature gradient across thermoelastic refrigerants. Based on our previous experience in integrating fatigue-free compression-based mechanism with heat exchanger/recovery subsystems, there is now a clear pathway toward substantially boosting the capacity and deltaT of thermoelastic cooling systems using active regeneration. Unlike other classes of caloric materials, thermoelastic materials have intrinsically high adiabatic deltaT (> 20 K) and the operation temperature range exceeding 100 K. We have recently showed that with our compression geometry, the metallic refrigerant can maintain its full cooling capacity without degradation for at least up to 1 million cycles. Since our system operates at 20-50 mHz, 1 million cycles are sufficient for a 10-year life of a residential cooling appliance.

In analogy to magnetocaloric cooling, which exploits active regeneration to go from the limited adiabatic deltaT of 3-5 K to a system deltaT of 20 K, we expect the thermoelastic counterpart to be able to achieve system deltaT > 50 K by properly implementing cascade active regeneration schemes. The starting materials will be NiTi tube bundles. A preliminary run of a single-stage regenerator has led to water-to-water deltaT of 22.5 K starting with the material deltaT of 8 K with the designed capacity of 50 W. We will also incorporate Cu-based thermoelastic materials into systems which can substantially reduce the required critical force required for the cooling mechanism as well as the overall refrigerant materials cost per system.  

Project Impact

The proposed concept is unique and practical as it will result in significant energy savings by utilizing non-flammable and environmentally safe metallic refrigerants to replace the vapor compression cycle to reduce its power consumption. The proposed project directly addresses remaining outstanding technological issues associated with thermoelastic cooling, so that the technology can be smoothly transitioned from its current state to higher TRL levels. Namely, we will address the problem of the high manufacturing cost and the high critical stress required for available thermoelastic materials by demonstrating prototypes based on Cu-based thermoelastic materials.

We propose to demonstrate deltaT approaching 100 K. Such a large deltaT can only be rivaled by the highest-performing vapor-compression devices, and if it can be realized, it has the potential to singlehandedly transform the HVAC industry and can lead to an entirely new generation of green cooling (as well as heating) devices with far-reaching energy saving potentials. Assuming the thermoelastic technology can make 40% energy savings, the overall saving will be 477 TBtu of primary electricity. Moreover, according to a report by the U.S. Energy Information Administration, the emission of greenhouse gases (HCFCs/HFCs refrigerants) is equivalent to 146 MMT of CO₂. If 50% of the vapor compressors using these GWP refrigerants are eliminated, the saving of CO₂ emission will be an additional 73 MMT.

Contacts

DOE Technology Manager: Antonio Bouza
Lead Performer: Ichiro Takeuchi, University of Maryland

Related Publications

Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cisse, Drew Stasak, Naila  Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle, Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi, “Fatigue-resistant high-performance elastocaloric materials by additive manufacturing,” Science 366, 1116 (2019).

Suxin Qian, Yunlong Geng, Yi Wang, Jiazhen Ling, Yunho Hwang, Reinhard Radermacher, Ichiro Takeuchi, Jun Cui, “A review of elastocaloric cooling: materials, cycles and system integrations,” International Journal of Refrigeration 64, 1-19 (2016).