A methodology is proposed to assess the savings achieved from the implementation of ECMs (energy conservation measures) in industrial plants with application for a combined cycle cogeneration plant. The analysis begins with the study of the operation of the system and a qualitative assessment of the changes resulting from the ECMs in the plant. The control volume is subsequently selected with the objective of minimising and focusing the efforts exclusively on the areas of the system actually influenced by the ECMs. An ANN (artificial neural networks) approach is proposed for the modelling stage and it is used to mimic the production and consumption of the system during the post-retrofit period in its configuration prior to the changes. Special attention is given to the selection of the variables used as predictors in the developed models, as well as to the determination of the relative influence of the inputs on the final models. Finally, the savings are calculated, and a critical analysis of the results is presented based on the comparison with the predictions obtained from the preliminary qualitative assessment. (C) 2015 Elsevier Ltd. All rights reserved.