A thermodynamic computer model named Thermodynamic Operation Point Simulation (Topsim) and programmed in Delphi, was developed to calculate the steady-state thermodynamic operation point of a fluidized bed process. The model was developed for a Glatt GPCG-1 fluidized bed unit in the top-spray configuration but the approach is perfectly transferable to other and bigger configurations. Convective and radiative heat losses were included in the calculation of thermodynamic response variables and because hear losses and outlet air thermodynamic properties are interrelated the strategy of varying the wet-bulb temperature was developed. The principle of this calculation method involves a gradual decrease of the process wet-bulb temperature until the heat loss appearing in the heat balance matches the actual heat losses. It was demonstrated that inclusion of heat losses improves clearly the model＇s performance and from validation experiments it was noticed that simulation of the thermodynamic operation point by Topsim is reliable. Hence, such a model helps in understanding the impact of process variables and ambient changes known as the so-called weather effect. Moreover the model can be applied in model predictive control of the thermodynamic operation point.