As the extreme heat effects of climate change intensify, it may not be possible to beat the heat by going inside. In fact, this is already the case for many people in vulnerable communities throughout the United States. According to studies by the National Institutes of Health and New York Department of Health, a growing number of heat-related deaths actually occur indoors, as people try to escape the heat.
With the National Weather Service predicting an unusually hot summer for the United States, heat vulnerability is a pressing issue and, according to researchers at Drexel University, it’s a challenge that doesn’t have a one-size-fits-all solution, particularly in urban areas where indoor temperatures can exceed those outside.
In a recently published review of research, Drexel’s Simi Hoque, PhD, a professor and head of the Architectural Engineering program in the College of Engineering, Leah Schinasi, PhD, an assistant professor who studies environmental and occupational health in the Dornsife School of Public Health, and Chima Hampo, a doctoral student in the College of Engineering, called for focused efforts to understand how indoor overheating affects the health and wellbeing of people in different regions of the country and how building design standards must evolve to ensure people can find refuge indoors. Schinasi and Hoque, who are also leading a National Institutes of Health study on the effects of chronic indoor heat exposure, recently shared some of the insights they gleaned from the research and discussed what individuals can do to beat the heat and address this pressing challenge.
What are the health consequences of building overheating?
Schinasi: The health consequences of building overheating are multi-faceted and may include acute (short-term) and chronic (longer-term) impacts. They include disrupted sleep, impaired cognitive functioning, respiratory distress or impaired lung function, reduced thermal comfort, injury, acute cardiovascular events, and chronic cardiovascular outcomes, such as diabetes or hypertension. Building overheating may also contribute to acute and chronic mortality outcomes.
How does climate change raise your concern about indoor heat stress?
Schinasi: Climate change is leading to unprecedented high outdoor temperatures. There is a high correlation between outdoor and indoor temperatures, and sometimes indoor temperatures can become even hotter than outdoor temperatures. Concerns over climate-change-associated indoor heat exposure are particularly strong for households living with poor or old housing infrastructure, or for whom air conditioning is inaccessible or unaffordable.
What socioeconomic factors cause some groups to be impacted most?
Schinasi: There are a number of social determinants that may lead to inequities in indoor temperature exposure.
Residential housing characteristics, such as roofing color, insulation and window-to-wall ratio, may have important impacts on indoor temperature exposures. The distribution of these factors varies according to race and income-based categories. In addition, access to air conditioning has been shown to be a powerful determinant of indoor temperature exposures. There is a growing body of literature also showing inequities in access to air conditioning according to racialized and socioeconomic categories.
Beyond access to air conditioning, there are also inequities in terms of households’ ability to afford the energy costs associated with air conditioning use. Even if households have access to air conditioning, they may not be able to afford the costs of using the system. These challenges are compounded by the fact that marginalized and lower income households also tend to be the most energy insecure owing to living in older, poorly insulated homes.
Land cover factors, such as disparities in tree canopy cover near one’s home or neighborhood, may also contribute to inequities in heat exposure and associated heat vulnerability.
Spatial inequities in urban land cover and housing characteristics that may enhance heat exposure have been linked with historical racist policies, such as redlining. For example, we conducted a study in Philadelphia that showed that a higher proportion of residential homes located in historically redlined neighborhoods had less tree cover and more flat/dark roofs, which could make indoor environments hot because they absorb heat.
There are a multitude of other factors that may contribute to these inequities, such as differences in work or school environment-related heat exposures, houselessness and access to preventative health care.
Do you have any examples of the health care costs associated with indoor overheating?
Schinasi: Extreme heat events are linked with excess morbidity and mortality events. These, in turn, are linked with tremendous monetary costs. For example, a two-week heat event in California in 2008 was estimated to result in $5.4 billion dollars in health costs. This was calculated as the sum of costs associated with deaths linked to heat, excess hospital admissions and excess emergency department visits during the heat wave.
Can you explain thermal adaptation and how that varies from person to person?
Schinasi: Thermal adaptation refers to the different ways that people make themselves feel comfortable in their indoor environments. People achieve comfort through physiological, psychological and behavioral means. When it’s hot indoors, people may adapt physiologically by sweating. But people also adapt psychologically, meaning they adjust their expectations about how it should feel. Finally, people adapt behaviorally to indoor environmental conditions by doing things like turning on air conditioning units or fans, adjusting their clothing or opening windows.
How might the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ (ASHRAE) model be adjusted to take into account more personal and cultural variations when it comes to thermal comfort? And how might this help to guide the design of residential buildings?
Hoque: ASHRAE has six metrics that account for thermal comfort — four that describe the environment: temperature, relative humidity, air speed/flow and mean radiant temperature; and two personal variables: metabolic rate and clothing insulation. It has been recognized for a long time that the standard model for thermal comfort was outdated and did not take into account cultural and biological variations.
In 1990s, this model was revised — one of the leading figures behind this was Gail Brager, who was one of my advisors when I went to grad school at UC Berkeley — and a new “adaptive thermal comfort model” was developed. It does a better job of accounting for personal and regional differences in thermal preference, expanding our understanding of how the human body adapts to different environmental conditions and the ranges that we find acceptable.
The design of buildings to accommodate this diversity is not trivial. Engineers like having well-bounded problems and human behavior is kind of a wicked problem, because there are so many factors — physical, psychological, phenomenological, physiological — that impact a person’s thermal comfort on a daily basis and these go well beyond changes in weather and HVAC system types.
We don’t really have a good answer for this. The adaptive comfort model tells us a little more about thermal comfort, but we are far from having a standard model. The idea of designing a building for health and wellbeing is more recent. We used to design buildings to not fall down and not make someone sick — that is to say we used to design around constraints (the bare minimum). But the idea of designing around wellbeing, to help people thrive, is fairly new. The WELL building standard tries to do this, but it’s a voluntary effort. I don’t know where it is going yet, but I’d love to see our building code move toward progressively improving health and wellbeing.
A number of the studies you looked at suggested optimizing construction practices – what sorts of practices should be adopted to better address the thermal comfort/safety challenges in urban areas?
Hoque: One thing we’ve been learning — from researchers who are looking at climate change impacts in urban areas, myself included — is that urban areas are far more vulnerable to heat stress events. This is because of the “heat island” effect, which takes into account the lack of green infrastructure, the amount of dark hardscape, heat rejection from air conditioning equipment, the lack of air flow and passive cooling opportunities, the poor condition of a great many urban buildings, flat roofs, etc. These are all factors that do not help cool a building.
There are ways to fix this, but it has to happen collectively. For example, the city has to invest in building an urban canopy of street trees, developers have to design more energy-efficient structures with white pitched roofs and homeowners have to agree to raise the setpoint temperature inside their homes to not overuse air conditioning.
At an individual level, what are some energy-efficient heat management practices for folks living in urban areas?
Hoque: I recently discussed this in an interview with WHYY-Radio – here are a few measures I’d recommend:
- The most cost-effective measure is ENERGY STAR levels (R-49) of cellulose insulation in the attic cavity.
- The second most cost-effective measure is a set-back thermostat that would set back the set point temperature 5 degrees for 8 hours (for example, when the occupants are out of the house).
- Coating a flat roof with a white elastomeric paint reduces summertime upper story temperatures by up to 5 degrees.
- The average savings per home is 15-18% after weatherization and up to 40% with a new heating system and weatherization.
I think many of the most vulnerable populations cannot afford to do some of these measures, so nonprofits like the Energy Coordinating Agency are really important because they audit, weatherize and upgrade HVAC systems at an average of 800 homes every year. This is very important. The problem with public resources for vulnerable populations is that it can be difficult to figure out what services you’re eligible for and how to access them. This is why programs like Built to Last came about, to make the process more streamlined and to sync up all the different services and resources for energy conservation and indoor environmental quality.
What are some easy ways for people to identify whether a residence has been designed for energy-efficient thermal management?
Hoque: I think that changing the thermostat to something that is programmable is an easy step. Checking to see if the HVAC equipment has been serviced yearly and that filters are changed 2-3 times a year is also not difficult to do — or to ask a landlord to do. Looking in the attic to see if it’s insulated and checking for drafts or leakiness around windows would be fairly simple. Beyond that, I think anyone can tell if their home is not designed well for thermal management when they get their first utility bill!
What steps do you see Philadelphia currently taking to address the issue of indoor heat stress and climate vulnerability in the summer? What steps should it be taking next?
Hoque: Philadelphia is taking this problem very seriously. We have a significant population of people who live in homes that are not air conditioned and every summer it’s getting hotter and hotter.
The city is trying to create a buzz around cooling centers, so that when the temperatures soar, there is a place for these folks to go to escape the heat that is building in their homes. Officials are making sure there are places in each of the city’s most heat-vulnerable areas, so residents can go to libraries, rec centers, senior centers, or even some parked buses.
I think there are also greening efforts across the city to increase the tree canopy to provide more shade. The Philadelphia Horticultural Society and Fairmount Park Conservancy are doing work in this arena; and, my colleague Franco Montalto, has been leading community-driven solutions to outdoor heat exposure, particularly in Hunting Park. I do think that cooling the outdoors will help, but we also need building-specific strategies, such as insulation in attics, painting roofs white, weatherization and modernizing HVAC equipment. These should be made into priorities particularly for those who live in substandard housing and in the most heat-vulnerable areas of the city.
Reporters interested in speaking with Schinasi should contact Greg Richter, assistant director, News & Media Relations, at 215-895-2614 or gdr33@drexel.edu. Reporters interested in speaking with Hoque should contact Britt Faulstick, executive director, News & Media Relations at 215.895.2617 or bef29@drexel.edu.
