Novel reduced GWP refrigerant compositions for stationary 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). 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 R-22 or R-410A type stationary air conditioning system designs, with concerns about capacity and flammability. Blended HFO based refrigerant candidates have been developed to provide better overall safety and performance, while retaining significant environmental sustainability properties versus the legacy refrigerants. Although 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 most nearly meet the most often cited sets of environmental, physical and performance properties for air conditioning. The candidates include DR-5A (R-454B pending) a 2L flammable gas that gives capacity performance near that of R-410A, a nonflammable composition for use to replace R-22 in high ambient temperature environments, DR-93 and a 2L flammable replacement for R-22 with a direct GWP of less than 150, DR-3. The trade-offs that exist between volumetric capacity, efficiency (COP), temperature glide, GWP value, and flammability have been explored and assessed. We report on the performance of the new compositions in both thermodynamic refrigeration cycle models at standard AC and high ambient temperature operating conditions, and in actual operating systems. These new compositions should provide useful options to help maintain the quality of life and health benefits from air conditioning and refrigeration, but in an energy efficient and environmentally sustainable manner.