Second-law and life-cycle assessment of CO2/R-1270 zeotropic blends in transcritical vapour-compression cycles under summer Arabian Gulf conditions

Abstract

At high ambient temperatures, transcritical carbon dioxide loses COP rapidly. Zeotropic blends, which may offer a helpful solution for sustainable cooling while maintaining efficiency, have been studied largely in temperate climates with 25 to 35 °C, while there is an absence of studies under harsh Gulf summer climate conditions. The method used in this investigation was modelling the performance of carbon dioxide/R-1270 at zero to 15% R-1270 from 40 to 48 °C. The model uses a published pressure-ratio-dependent isentropic efficiency correlation, along with energy, exergy, and TEWI analysis. The blend lowered COP at every composition and ambient temperature, by −5.2% at 15% R-1270 and 40 °C. At 15% R-1270, the mixture's critical temperature increases by 6.2 K, against the 14 K required to bring the gas cooler outlet below the critical temperature. The internal heat exchanger (IHX) helped recover COP, with recovery increasing as ambient temperatures increased, from +7.7% at 40 °C to +13.0% at 48 °C. A takeaway from this investigation is that effort on improving internal heat exchange and expansion recovery systems in refrigeration may offer benefits over zeotropic blends in harsh Gulf climates.