Indoor Environmental Quality in Naturally Ventilated Office Buildings and its Impact on their Energy Performance

During the last two decades the significance of indoor environmental quality in buildings has been appreciated, not only in relation to thermal comfort, but also to indoor air quality. Ventilation is an important tool for securing both a good indoor climate and air quality. However, in buildings without mechanical ventilation and air conditioning systems (which comprise the majority in most European countries) natural ventilation presents the only means to satisfy indoor air quality needs. Natural ventilation is, however, a process that is difficult to control, whilst its impact is difficult to quantify by the buildings‘ occupants in real life. A field survey, carried out by the authors, is described in this paper. This highlights both the potential and the constraints of natural ventilation in office buildings. The survey focused on the two main parameters, which determine indoor environmental quality, namely thermal comfort and air quality. The data collection strategies employed were in-situ measurements to determine and evaluate the prevailing conditions, and questionnaires, which monitored and evaluated the perceptions held by the buildings‘ users in relation to those conditions. The latter confirmed the occupants‘ difficulties and dissatisfaction with respect to controlling prevailing thermal comfort conditions, whilst the former demonstrated the role of natural ventilation in reducing CO 2 and particulate matter concentrations. The survey also underlined the ineffectiveness of natural ventilation when attempting to control relative humidity levels and the overall difficulties in achieving a satisfactory energy performance of the building.