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UNIVERSITY OF NOTRE DAME DU LAC

Every year the United States consumes 2.4 Quadrillion British Thermal Units (QBtu) and emits 420 million metric tons (MMT) of Carbon Dioxide in order to cool our living, working, storage and transportation spaces. Nearly all of this 2.4 QBtu of cooling energy is provided by high grade mechanical or electrical energy, the majority of which originates from burning fossil fuels. The most popular refrigeration and air conditioning systems are vapor compression systems, which are reliable, relatively inexpensive and well established. While current refrigerants (e.g., HFC-134a and HFC-410a) have no ozone depletion potential, they have significant Global Warming Potential (GWP) 1430 and 2000 times that of Carbon Dioxide. A suitable working fluid system is probably the single most important factor in any refrigeration system. A very attractive refrigerant is Carbon Dioxide. Unfortunately, running Vapor Compression refrigeration systems with pure Carbon Dioxide requires prohibitively high pressures. One solution is to run the Carbon Dioxide Vapor Compression system with a co-fluid that reversibly absorbs the Carbon Dioxide, thus greatly reducing the pressure requirements. Desirable properties of the co-fluid include low volatility and good thermal and chemical stability. Ability of the co-fluid to lubricate the compressor would be an added advantage. We hypothesize that ionic liquids, which are non-volatile liquid salts with zero global warming potential, could dramatically improve the efficiency of Vapor Compression systems if they are designed and synthesized with specific characteristics as a co-fluid for use with Carbon Dioxide. We will make both fundamental scientific inquiry in the form of molecular modeling and experimental synthesis and characterization of previously undiscovered compounds with laboratory investigation of full-scale air conditioning systems. We will demonstrate a co-fluid Vapor Compression cycle based on Carbon Dioxide and ionic liquids; extend system models to identify the characteristics of an optimal ionic liquid co-fluid; use atomistic simulation and experimentation to discover these fluids; and ultimately demonstrate an operating Carbon Dioxide-ionic liquid system with efficiency well beyond that of existing air conditioners using HFC-410a refrigerants systems.

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