The Link between Buildings and Cognitive Performance

Abstract

In North America, buildings account for an estimated 40% of total energy use and carbon emissions (Nägeli et al., 2018) and are where people spend over 90% of their time (Klepeis et al., 2001). A historical focus on energy efficiency has led to strategies that often degrade indoor environmental quality and in turn, occupant health (A. K. Persily & Emmerich, 2012). Recent attention has shifted towards designing and operating buildings for human health, but there are still questions around the benefits of building operation for human occupants and how to balance these considerations with building energy expenditure. Building heating, ventilation, and air conditioning systems are one pervasive building component that are key to this balance since these systems consume substantial amounts of energy to thermally condition and ventilate indoor spaces, which in turn, impacts occupant health in many ways. Much of the current building stock is operated to conditions set forth by standards that are not designed to promote human health. Accordingly, substantial amounts of energy are being consumed to condition and ventilate spaces to settings that do not necessarily support occupants and their activities. In response to this, we investigate indoor air quality, as influenced by building ventilation and occupancy, and indoor thermal conditions, as influenced by space conditioning, as two main indoor exposures that are influenced by these systems and also impact occupant health. We then assessed occupant cognitive performance and perceptions of the indoor environment with participant test and survey responses collected through our smartphone-based research application. We used this acute exposure and outcome data to model associations between indoor air and thermal conditions and metrics of cognitive function and thermal sensation. Collectively, the model estimates show that lower carbon dioxide concentrations, achieved through higher outdoor ventilation, are consistently and significantly associated with improved cognitive test scores. For thermal conditions, we observe that a normative range of roughly 22-26 ⁰C can support cognitive performance and thermal sensation in a variety of settings and that temperatures above and below this range show evidence of decreasing cognitive test scores. The relationship between indoor air moisture and cognitive performance is less clear from this work. There is preliminary evidence that common thermal modeling approaches, such as the use of temperature and relative humidity as separate thermal variables or the use of pervasively used thermal comfort models, might underestimate the potential importance of indoor moisture with respect to occupant outcomes. We explore enthalpy as a potentially useful combined temperature and moisture metric and observe preliminary evidence of consistent associations between higher values of indoor enthalpy, up to approximately 55 kJ/kg, and improved cognitive test scores. Additional research is needed to understand how these associations might vary in wider exposure ranges, across different built environment settings and populations, and the potential implications for building energy expenditure. Overall, these collective results suggest that focusing on increasing outdoor air ventilation and maintaining temperatures within a normative range of approximately 22-26 °C, can support occupants and their activities in working and learning environments.