A comprehensive simulation model, based on the TRNSYS program, for the evaluation of thermalstorage system behaviour in building climatization is presented here. The algorithm is applied to the study of a typical office building in presence of an ice or water storage. Possible economic advantages are presented and analysed. The remarkable differences obtained with different plant options confirm the necessity of an accurate study and justify the use of comprehensive computer models. The results suggest better opportunities with water storages because a water tank can give further economic savings in presence of heat pumps in winter.