The calculation of mixture dew and bubble points and the simulation of fluid processes occurring under specified enthalpy or entropy changes are important in the refrigeration and other industries. These calculations are typically carried out using an empirically based multiparameter equation of state approach, such as that incorporated in the industry-standard REFPROP software package. We consider the capabilities of more fundamentally based molecular simulation methodology for performing these calculations. This approach requires a much smaller parameter set, can reliably extrapolate beyond the thermodynamic conditions used to determine the parameters, and can be used for the prediction of multiple properties. We briefly review relevant algorithms and focus on a set of Monte Carlo molecular simulation methods for accomplishing the tasks. We demonstrate their applications to the calculation of isoenthalps for the two pure fluid alternative refrigerants R134a (CH2FCF3; 1,1,1,2-tetrafluoroethane) and R143a (CH3CF3; 1,1,1-trifluoroethane), and to the simulation of all stages of a vapor-compression refrigeration cycle involving a binary mixture of the refrigerant R32 (CH2F2: difluoromethane) and R134a of 30 mass % R32. The molecular simulation algorithms produce results for these problems in good agreement with those calculated by REFPROP.