Mortality and morbidity associated with extreme summer heat and poor air quality continues to be one of the most pressing human health challenges in cities and is likely to be exacerbated in the future due to urban growth and climate change. Heat is currently the leading weather-related cause of death in the developed world (e.g. CDC 2004), and future heat vulnerability for the elderly is projected to increase substantially in the coming decades (Sheridan et al., 2012).
Recent extreme heat events such as the May 2015 heat wave in India that saw record temperatures near 50oC and resulted in more than 2500 deaths, have underlined the importance and urgency of the problem. Traditional epidemiological studies of the health effects of heat and air quality focus on outdoor environmental conditions. This approach is suitable for assessing heat-health risks for populations that spend much of their time outdoors (e.g. homeless, construction workers, etc). However, as was the case of the European heat wave of 2003, the particularly vulnerable population was the elderly, and in particular, elderly who lived on the top floor of a building that lacked air conditioning (Mavrogianni et al., 2012). Typical urban residents spend more than 85% of their time indoors (Klepeis et al., 2001)—and some of the most vulnerable populations (e.g., the elderly) spend an even higher fraction of time indoors.
While the indoor environment is coupled with the outdoor environment there are key differences both in terms of air quality and thermal conditions. With respect to thermal environment, for buildings without air conditioning, this coupling includes variations in indoor air temperature that depend on building construction characteristics, location within building (e.g. top floor, south façade), occupant behavior, internal loads, ventilation, and infiltration. Indoor air quality, on the other hand, is driven by the relative magnitude of each mode of air exchange (e.g. infiltration vs. filtered mechanical ventilation) and emissions and secondary reactions of air pollutants indoors.
Hence, there is a need to better understand the relationship between indoor and outdoor environments, and how this relationship is affected by occupant behavior and building construction and management practices. In the case of air conditioned and mechanically ventilated buildings a scenario of particular interest is that of coincident heat waves and power outages producing very unhealthy indoor environments. This paper discusses a newly funded research project that addresses these issues, with an emphasis on assisted living facilities using the city of Houston Texas, USA as the research test bed. It will introduce some of the key mechanisms that drive differences in indoor and outdoor conditions and present some early findings related to risks of coincident heat waves and power outages or equipment failures in buildings.