In this work, a novel detailed mathematical model for the performance assessment of diabatic compressed air energy storage (D-CAES) systems with underground storage site is proposed. The model was implemented in Matlab environment and it was validated using the D-CAES Huntorf plant data, demonstrating a close agreement with the data reported in literature. The analysis of some case studies of the D-CAES plant showed that the characteristic curves of the compressors, that were assumed for the operation in steady state conditions, are not suitable for modeling the operation in time-dependent conditions. Thus, different characteristic curves of the compressors and turbines were identified in such a way that the operation points of turbomachinery lay within the admissible range during the entire process sequence, in steady state or time-dependent conditions. Furthermore, the analysis demonstrated that the presence of the throttling valves in the charging and discharging circuits is preferable due to a higher simplicity of construction and regulation despite a low increase of the fuel consumption in the combustion chambers. (C) 2016 Elsevier Ltd. All rights reserved.