For energy savings, DCV systems are more and more used in ventilation systems but toestimate their energy savings, variation of occupation in the building (in time and number ofperson) must be estimated. We have enquired on real occupation on site in 27 offices and 13meeting room in France. Occupation rates have been monitored either by webcam or byenquiry to the users. Results show very low occupation rates in meeting rooms although mostpeople feel they are very occupied. Yet effective time of meetings and number of occupantsare less than expected. Even offices are not occupied all day long considering people move alot in their job. The conclusion is that DCV systems offer a great potential for energy savingsbut of course should be characterised and dimensionned properly to achieve good results.