Heat pump systems have gained significant market shares in Europe recently. The control strategy is an asset for the efficient operation of these thermodynamic systems; especially with compact integrated components. The predictive control, which allows fast system stabilization, is based on the description of the system physical behavior. Thus, dynamic modeling is needed for the development of such control. The model has to represent the system response to usual external perturbations met during current operation such as the variation of air temperature and air mass flow rate. The aim of this paper is to present a dynamic model of a thermodynamic system developed in the Dymola environment, which is an object-oriented modeling environment. The heat-pump components are created separately as individual objects, and then connected to form the system. The model of each component is described and the responses to different perturbations are detailed. Simulation results are compared to test results in order to validate the model.