To apply the regulation energy performance of commercial and service buildings (RECS), to the small service buildings without climate (PESsC), the Itecons developed a tool of dynamic simulation simplified (monozone), applicable both as new buildings as existing buildings. It is a tool where was tried to conjugate the simplified dynamic calculus in accordance to EN ISO 13790, as recommended in RECS, with functionalities of other tools developed by Itecons, namely the mapping and thermal characterization of the envelop, the inventory of lighting systems and definition of utilization profiles, the automatic verification of requirements and the study of improvement measures. Available in: www.itecons.uc.pt/p3e.