Climatisation and natural ventilation concepts are today, in most countries, considered to be an essential aspect of the building project. In fact they are utilised to guarantee summer thermal comfort and indoor air quality control. Also there are many other advantages including low energy use, reduction of noise levels and easy plant maintenance. In recent years the use of hybrid ventilation systems in office buildings has been developed. The achievement of thermal comfort conditions in buildings is an important aim in order to satisfy occupants. To achieve a high level of life quality a study of climatic parameters of the ambient air is needed. International Standard ISO 7726 and ASHRAE Standard 55-81 define the values of parameters affecting thermal comfort in offices. The aim of the present work is to evaluate the fluid dynamic phenomena connected to the running of the air conditioning and natural ventilation systems in an innovative office building, constructed in central Italy, aimed at achieving energy optimisation with good thermal comfort. This building has been monitored and the main fluid dynamic data of the air have been recorded. In addition the recorded values have been related to external parameters including solar radiation, wind speed and wind direction, to verify the indoor conditions in relation to the energy use of the building and to outdoor conditions. This research has been accomplished using automated monitoring for indoor data acquisition, a microclimatic station and a meteorological station equipped with the probes needed to measure the external environmental parameters. The experimental data corresponding to a monitoring period are reported. Results verified the performance of the measuring system developed for this project. They also provided information about the ventilation behaviour and thermal comfort conditions in the building under various sets of climatic conditions.