CO2 based ventilation control is an eligible technology to reduce energy consumptions concerning ventilation air treatment and its distribution in particular in presence of highly variable occupancy. An experimental assessment of the performances of this control strategy is illustrated in this paper. The study refers to a historic building in Venice recently refurbished and subject to a preservation order. It concerns a demand controlled ventilation (DCV) system installed in a part of the building transformed in a university library and based on the use of CO2 sensors. A building management system (BMS) able to measure and record the required data was used as a tool for long term monitoring of the HVAC system. A comparison with alternative solutions was also carried on, The results permit to quantify remarkable energy savings, particularly strategic in the energy retrofit of historic buildings especially in presence of preservation orders. But the investigation highlights also the peculiarities of CO2 based ventilation control in meeting the indoor comfort requirement which suggest a systematic use of long term assessment to verify control efficacy in different operating conditions. (C) 2017 Elsevier Ltd. All rights reserved.