An azeotropic mixture of R32/R290 is proposed for both building air-conditioning and ocean thermal energy conversion (OTEC) applications. R32/R290 is an environmentally safe working fluid mixture with no ozone depletion potential (ODP) and low global warming potential (GWP). This mixture can successfully replace R410A used in many residential air-conditioners and heat pumps since its GWP is quite low, about 25% of that of R410A. The same mixture also can be used in OTEC power plants to replace conventional working fluids of medium vapor pressure. Due to the increase in density, a significant reduction in equipment is expected, which consequently will result in an initial cost reduction.