Many market forecasters confidently predict that the global heating, ventilation, and air conditioning (HVAC) market will grow rapidly to approximately $155 billion USD by 2022, up dramatically from its 2013 estimate of $91 billion, due to construction projections and urbanization in developing nations.
How do we sustain that growth using current vapor-compression technology? Developed for commercial applications during the first half of the 20th century, modern vapor compression refrigeration systems power the air conditioning in our homes, office buildings, and cars, as well as satisfy our residential and commercial refrigeration needs.
While vapor compression is a very mature and relatively inexpensive technology, it is nearing the limits of potential energy efficiency improvements, and yet its use still represents a substantial proportion of our energy consumption, second only to lighting in the U.S. alone. Liquid refrigerants in common use today often escape into the environment, accumulate in the atmosphere when initially closed systems develop leaks with time, and cannot be re-captured.
An alternative technology has actually been with us for quite some time. Caloric materials and compounds that can generate strong cooling effects when cyclically acted upon by magnetic, electric, or mechanical forces, can be incorporated into refrigeration systems that are dramatically more energy efficient than current vapor-compression models.
When my late colleague, Karl Gschneidner Jr., and I discovered what is known today as the “giant” magneto-caloric effect in a gadolinium alloy in 1997, we were presented with a promising new avenue for cooling systems. We partnered with Astronautics Corporation of America to build a successful prototype refrigeration mechanism. Despite much, mostly uncoordinated, subsequent research in the materials science and engineering communities, and demonstration models being built by various teams all over the world, the technology as it now exists has remained largely behind the doors of research institutions, failing to make the leap from fundamental research to applied technology.
The central challenge of bringing caloric cooling technology to market is finding affordable high-performance caloric materials. Like Peltier effect in thermoelectric devices, caloric effects underpin the efficiency of caloric refrigeration systems. Mirroring the materials base for thermoelectric applications, the pool of functional caloric materials on hand is severely limited. Only three materials are presently available for integration into magneto-caloric devices operating at room temperature: elemental Gd and its alloys with other rare earths, La(Fe1-x-yMnxSiy)13Hz, and MnFe(P,Si,B). Best known for its medical applications, shape-memory Nitinol, NiTi, is the only material available for elasto-caloric (a.k.a. thermos-elastic) systems, and BaTiO3-based multilayer capacitors – for electro-caloric devices. Although successful laboratory prototypes have been demonstrated, low cooling powers at full temperature spans and high costs, both of which are material-driven, preclude the much-anticipated transition from the vapor-compression-based present to a more efficient and consumer-friendly caloric cooling and heat pumping future.
Last year a team of national laboratory, academic and industry scientists and engineers assembled as the research consortium CaloriCool, funded by the U.S. Department of Energy (DOE), to concertedly address and pursue materials-related technical challenges and to substantially accelerate the penetration of caloric cooling systems into the marketplace.
Member of the U.S. DOE Energy Materials Network, the consortium is set to address foundational challenges that include rapid discovery of advanced caloric materials, their evaluation and processing to ensure lifetime stability, rapid assessment of material performance, regenerator design, materials-based economic analyses, and validation and technology transfer. The consortium’s ultimate goals are to pick up the pace in developing caloric materials and, therefore, ensure adoption of caloric cooling and heat pumping technologies across a broad spectrum of applications within a decade, and establish the consortium as the national resource and international authority in caloric materials within five years.
We believe the potential gains in energy efficiency and new features that the emerging solid-state, caloric cooling technologies have to offer are too significant to ignore.
Vitalij K. Pecharsky is a senior scientist and group leader at the U.S. Department of Energy’s Ames Laboratory, an Anson Marston Distinguished Professor of Materials Science and Engineering at Iowa State University, and the director of CaloriCool®. CaloriCool® is an early stage research consortium funded by the U.S. Department of Energy’s Office of Advanced Manufacturing of the Energy Efficiency and Renewable Energy (EERE).