The principal aim of this paper is the study of a thermodynamic model that simulates the working of a vapour compression refrigeration plant. The model allows the evaluation of plant performances when the compressor capacity is regulated varying its velocity by means of an inverter inserted into the compressor electric motor feeder. This type of control allows to match continuously the compressor refrigeration capacity to the load, determining an energy saving in comparison with the classical thermostatic control. In particular, in this paper the outputs of the model are compared with the experimental results. The vapour compression experimental refrigeration plant, whose evaporator is located in a commercially available cold store, presents a semi-hermetic reciprocating compressor able to work with the R22 and some its substitutes, and designed for a revolution speed corresponding to a 50 Hz frequency of a compressor electric motor supply current. The comparison of model and experimental results is realized by varying the supply current frequency of the compressor in the range 30–50 Hz using the R407C (R32/R125/R134a 23/25/52% in mass) that represents the most suitable working fluid for the R22 substitution. The model-experimental comparison results reported in terms of condensation temperature, compression ratio, condensation power and Coefficient Of Performance are completely acceptable. Moreover, an exergetic analysis is realized to explain the performances of the plant components when the compressor speed is varied. Copyright © 2004 John Wiley & Sons, Ltd.