In 2014, European F-gas directive plans the prohibition of fluorinated working fluids with GWP of 2500 or more from 2020. Consequently, new working fluids have to be considered in the future such as HydroFluoroOlefin, carbon dioxide or mixture of HFO with hydro-fluoro-carbon or CO 2. The knowledge of the thermo-physical properties of working fluid is essential for the evaluation of performance of heat pumps, ORC and refrigeration. Herein, several " French " laboratories proposed to investigate the thermo-physical properties of the R744 + R1234yf binary system. In 2014, Juntarachat et al. measured and correlated vapour liquid equilibria including mixture critical point. New experimental determinations for density and viscosity using vibrating densitometer and capillary viscometer are presented. Also, enthalpies of mixing are determined using BT-215 Calvet calorimeters. In addition, molecular simulation based on empirical force have been realized. Several thermodynamic and transport properties have been obtained using Monte Carlo and Molecular Dynamics simulations. The PPR78 cubic equation of state and a multipolar version of SAFT-Mie are used to predict the new experimental data for thermodynamic properties. The model developed is used as an input to simulate the performance of new heat pump system. An experimental heat pump is used to evaluate the achievable energy efficiency with this mixture in real machines with one test molar composition of 5% R1234yf). The optimal pressure and COP will be compared to those obtained with pure CO 2 in similar operating conditions.