Refrigerant, HFO, GWP, Flammability, Air Conditioning
The current fluids most widely used for small and mid-sized air conditioning systems globally are R-410A and R-22. While these fluids have many positive attributes for cooling, they are the subject of valid criticisms regarding their high direct global warming potential (GWP) and, in the case of R-22, ozone depletion potential (ODP) also. In the interest of improved environmental sustainability, a new class of refrigerant molecule has been developed, the hydrofluoroolefin, or HFO. While the very low direct GWP values of these molecules are attractive, none of the HFOs by themselves are fully satisfactory for use in conventional stationary AC system designs, for reasons of concern about low capacity and flammability. Blended refrigerant candidates have been developed to provide better overall safety and performance, while retaining significant environmental sustainability properties versus the legacy refrigerants. There is as yet no universal agreement on what are the most critical properties for air conditioning fluids. No single candidate has yet been developed that meets every proposed requirement for a refrigerant fluid. This paper discusses three candidate fluids that have been developed to meet three of the most often cited sets of environmental, physical and performance properties for air conditioning. Each of these candidate fluids possesses desirable, but different sets of properties. The trade-offs and relative performance and environmental merits of each will be discussed. The three fluids vary in direct GWP values, flammability, capacity, and critical temperature. One is a 2L flammable gas that gives capacity performance near that of R-410A. One is a nonflammable composition for use to replace R-22 in high ambient temperature environments. The third is a 2L flammable replacement for R-22 with a direct GWP of less than 150. In designing and evaluating these new compositions, the trade-offs that exist between refrigeration capacity, efficiency (COP), temperature glide, GWP value, and flammability have been explored and assessed. We report on the comparisons of these compositions in AC measurement and modeling work. The new compositions have been evaluated with thermodynamic refrigeration cycle models at standard AC conditions, and at high ambient temperature operating conditions, and show good performance. Testing is underway to evaluate performance of these new compositions in laboratory equipment and in actual operating systems, as compared to R-22 performance in the same or similar systems. The status of the testing and some results generated to date will be reported in this paper. These new compositions should provide useful options to help maintain the quality of life and health benefits that accrue from air conditioning and refrigeration, but in an energy efficient and environmentally sustainable manner.