DCV systems have proved to be energy saving with correct IAQ in previous studies. In order to achieve correct performance, these systems must be properly designed and tested. The purpose of this study is to identify the possibility of using presence sensors based on movement detection to evaluate the number of people present in a room, and also gather some more information about the real occupation rate of meeting rooms. For that, an experiment in several kinds of meeting rooms, located in different buildings and having different uses has been run. The study is not finished yet, but the analysis of the first results allow to have a good adequation between the information given by the sensors and the effective number of people present in the room. It also shows with quantitative information, how the occupation rate of meeting rooms is low, and the potential of energy savings that is possible to realise by adapting the room ventilation flow rate to the real occupation rate.