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 CO2 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. Key words: Indoor air quality, thermal comfort, energy performance, natural ventilation, office buildings, occupant survey. Performance Evaluation of a Wall Mounted Convector for Pre-heating Naturally Ventilated Spaces A A Elmualim1, H B Awbi1, D Fullford1 and L Wetterstad2 1School of Construction Management and Engineering The University of Reading, United Kingdom 2Wetterstad Consultancy, Lddekpinge, Sweden Abstract This paper presents the results of performance monitoring under real winter weather conditions, controlled laboratory testing and computational fluid dynamics (CFD) analysis of a wall mounted ventilation air inlet heat convector. For real winter weather monitoring, the wall-mounted convector was installed in a laboratory room of the Engineering Building of the School of Construction Management and Engineering. Air and hot water temperatures and air speeds were measured at the entrance to the convector and in the room. The hot water temperature was controlled at 40, 60 and 80 C. The monitoring results were later used as boundary conditions for a CFD simulation to investigate the air movement in the room. Controlled laboratory testing was conducted in laboratories at the University of Reading, UK and at Wetterstad Consultancy, Sweden. The results of the performance investigation showed that the system contributed greatly to the room heating, particularly at a water temperature of 80 C. Also adequate fresh air was supplied to the room. Such a system is able to provide an energy efficient method of eliminating problems associated with cold winter draughts.