Caloric Systems for Cooling, Heating, and Work

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Global demand for thermal services including space cooling, heating, refrigeration, and thermal storage is responsible for approximately 40-50% of global energy consumption. According to a recent study from Lawrence Berkeley National Laboratory, the world may see an additional 700 million air conditioners by 2030, and 1.6 billion of them by 2050. This is but one example of how new demands can result in additional electricity generation and GHG emissions “like adding several new countries to the world.” Current technologies for heating and cooling are mature, but use working fluids with ozone depletion, global warming, and safety concerns. A global effort is underway to commercialize replacement technologies new cycles using solid materials have been identified as promising alternatives. Caloric materials are solid substances with one or more reversible work modes defined by their dominant ordering mode. Examples include magnetocaloric (MC magnetic order), elastocalorics (eC structural order), and electrocalorics (EC electrical order). Materials with more than one work mode are multicaloric. Of particular interest are materials exhibiting first order phase transformations providing large changes in entropy with temperature and applied field. In practice, the use of caloric materials is analogous to vapour-compression systems where adiabatic work input results in a reversible temperature change. One of the challenges of using caloric materials in heating or cooling systems is the magnitude of the reversible temperature change, and the temperature range over which the response is significant. To overcome this, an active caloric regenerator (ACR) uses one or more materials in a layered regenerator structure so that a cascade of cycles is created. In effect, heat is pumped from one location, or material, to the next, across a desired temperature span. Many caloric materials suffer from similar problems of limited caloric response with respect to temperature and field suggesting the need for an ACR cycle. The objective of this research program is to develop efficient caloric systems for energy conversion. Three areas are addressed: (1) developing our understanding of caloric thermodynamics, (2) determining the processes which enable high performance, (3) developing efficient devices that are cost effective.