Indoor environmental quality and occupants' comfort: a comprehensive understanding of humans' perception and adaptiveness

In recent years, a number of studies in the realm of Indoor Environmental Quality have been set to better understand occupants’ perception and behaviour phaenomena. Differences in people’s perception of the indoor environment, personal preferences with regard to the air quality, thermal and visual comfort, as well as physiological, psychological, cultural, economic and sociological aspects could have a relevant impact on the building energy performance. At the same time, indoor environmental conditions could considerably affect health, productivity and comfort of people. Due to the dual nature of this problem, on one hand a recent increase in efforts toward developing dependable models of occupants’ presence and interactions with building control systems has been observed; on the other hand, more strictly regulations have been introduced and new standards have been developed in order to ensure an even higher quality of indoor environmental conditions. However, due to the complexity of multiple interacting factors, there is a lack of knowledge focusing on a holistic comprehension of users’ sensation and behaviour. The present contribution undertakes an empirically-based study in the area of Indoor Environmental Quality and represents an attempt to provide an additional contribution in the fields of humans’ perception and adaptiveness. For this purpose, two significantly different building typologies were investigated: the first one is a mechanically cooled and heated classroom at the University of Rome “Tor Vergata”, with “passive” occupants and a short-term monitoring and surveys; the second one is a naturally ventilated office area at the Vienna University of Technology, with “active” occupants and a long-term high-resolution monitoring. Starting from raw data, comparisons and structured analysis were carried out. This allowed for objective and subjective assessments of the indoor environmental conditions across different seasons (summer and winter periods), occupants’ conditions (steady state or transient) and system operations (ventilation system on/off). The results generally shed light on the complexity in the evaluation of the indoor environmental conditions related to inhabitants’ comfort perception in buildings. The main critical issue lies in the “noise” generated by the simultaneous presence of a large set of possible factors influencing users’ perception and behaviour. As a consequence of the subjective nature of human perception, the generated occupants’ behaviours are not easy to predict. Despite it is anything but trivial to identify unambiguous and clear “signals” of individual causal factors, it is hard to quantify their “weight” and relative importance. Even under deeply different boundary conditions (conditioned building versus naturally ventilated building, mediterranean versus continental climate, pronounced differences in the cultural, social and economic backgrounds of occupants), the obtained results mainly reveal consistent common outcomes and allowed for some general considerations: the higher the hygro-thermal comfort satisfaction, the higher the Indoor Air Quality perceived. As a consequence, a limited awareness in the perception of the real Indoor Air Quality, expressed in terms of air exchange rate and conventionally represented by the carbon dioxide concentration, has been observed, especially when the overall indoor environmental conditions were perceived as comfortable. This bias related to the human subjective perception represents a significant matter, not only in terms of comfort evaluation and control-action behaviours, but also in terms of effects on occupants’ health and well-being and the risks connected to the long-exposure to indoor air pollution. Future research in this scientific area are mainly related to the development of more reliable occupancy-related models for building applications and simulations, based on the improvement of a more comprehensive understanding of humans’ perception and behaviour phaenomena. The further broadening of knowledge in this field, coupled with the development of more accurate regulations and standards focused on the rational use of energy, represents an important challenge in the context of the future sustainable development.