Image Courtesy of Cathleen Liang.
Even before the pandemic, people spent about ninety percent of their time indoors. Given how many hours we spend in these spaces, it is important to think about how changes in building design or operation impact indoor air quality.
The burning of fossil fuels contributes to global warming by accumulating large quantities of carbon dioxide and particulate matter smaller than 2.5 microns in the atmosphere. The latter is a pollutant with one of the largest health effects—despite its minuscule size, it can both cause and exacerbate cardiovascular diseases, respiratory diseases, and cancer.
While many factors contribute to emissions of carbon dioxide and particulate matter—wildfires and cars, for example—a major source of air pollution originates from buildings and building-related operations. According to the US Energy Information Administration, residential and commercial buildings consume forty percent of all energy in the US. This issue makes buildings an important target for measures that increase energy efficiency and reduce carbon dioxide and pollution emissions.
Drew Gentner, Yale professor of Chemical & Environmental Engineering, and Kenneth Gillingham, professor of Economics, along with their colleagues from Yale’s Solutions for Energy, Air, Climate & Health Center, embarked on a necessary interdisciplinary investigation. In their new study, published in Science Advances in August, the researchers used the Yale-NEMS (National Energy Modeling System) model, which models the effects of various building energy efficiency scenarios they designed based on literature. Leveraging their perspectives on the dynamics of air pollution in indoor and outdoor spaces, they investigated scenarios that could impact carbon dioxide emissions associated with energy use and energy-related emissions of outdoor pollutants.
The project was motivated by the desire to both improve human health and help us tackle climate change. “It is not a new issue, and we have known for a long time how important it is, but quantifying the effects of strategies to address climate change is more relevant now than ever,” Gillingham said.
Energy Efficiency Scenarios
Gentner and Gillingham’s study evaluated how energy efficiency measures could improve building tightness, a measure of outward and inward air leakage in buildings. These energy efficiency measures included changes to infiltration, natural ventilation, and heat, ventilation, and air conditioning (HVAC) recirculation adoption. The researchers’ goal was to explore ways to reduce energy losses associated with air leakage from indoors to outdoors, and vice versa.
To do so, they created two scenarios: “Intermediate EE” and “Optimistic EE.” The “Intermediate EE” scenario provides close to twenty percent increased efficiency on all building appliances and equipment. In this scenario, the annual efficiency improvement from better building shells—which separate the building’s interior spaces from its exterior spaces—can achieve cumulative improvements of more than fifty percent. The “Optimistic EE” scenario is a more idealistic model, allowing for fifty percent increased efficiency in appliances and equipment, along with more than sixty percent of cumulative annual efficiency improvement from increasing the quality of building shells.
These two scenarios are based on possible future energy efficiency improvements for building services and shell structure materials. Shell structure materials are used to secure the building composition by transmitting applied forces on the surface. The energy efficiency improvements address space heating and cooling, water heating, lighting, refrigeration, and culinary services for residential and commercial facilities. They also address building shell efficiency improvements in the residential, commercial, and industrial sectors for both existing and new structures.
Another focus was improving recirculation with filtration, which can help mitigate indoor concentrations of particulate matter. Considering how energy efficiency is greatly related to the emission of energy production-related pollutants, these two scenarios also provide estimates for how many premature deaths in the United States would be avoided in each case.
Using the outputs of the Yale-NEMS model, along with the building energy efficiency scenarios, the researchers evaluated how concentrations of particulate matter could change indoors as a function of building tightness. The study examined how the two building energy efficiency scenarios would impact air quality across the entire US housing stock.
The researchers explored the interconnectivity of outdoor and indoor air quality by looking at the changes in infiltration while also considering the variations in indoor emissions across houses in the US. These emissions are closely related to cooking activities, and the resulting concentrations are impacted by the presence of particle filtration—which, in turn, is related to building HVAC systems.
Compared to the reference case of the energy efficiency scenarios, the Yale-NEMS model predicted that decreasing energy-consuming activities could improve general outdoor air quality. On a larger scale, it also shows that indoor air quality related to building energy efficiency improvements depend largely on indoor emissions and home design characteristics. According to the research team’s findings and interpretation, by 2050, both efficiency scenarios could yield a six to eleven percent reduction in energy-related carbon dioxide emissions and an eighteen to twenty-five percent reduction in the main particulate matter emissions. Ultimately, following the energy-saving scenarios could reduce outdoor emissions, potentially saving 3,700 to 7,800 lives per year in the United States by 2050.
A Call to Action
Unfortunately, the study’s findings also show that energy efficiency improvements could negatively impact indoor air quality in some homes. Due to lower air exchange rates, infiltration caused by tightening the building shell for energy efficiency gains might result in greater exposure to indoor contaminants in some buildings. The observed changes in indoor air quality show that it is essential to increase awareness of indoor particulate matter emissions. Because of this, indoor air filtration improvements should also accompany energy efficiency improvements. This might be especially significant for low-income housing, which tends to have inadequate indoor air filtration due to the usage of more health-damaging materials.
Still, even after accounting for changes in indoor air quality, the thousands of premature deaths that could be avoided by improving the energy efficiency of buildings should not be neglected.
Overall, estimates of public health improvements reveal the urgency of reducing the outdoor air or outdoor pollutant emissions associated with energy use. “Attention to ventilation strategies, indoor emissions, and investments in interior air recirculation systems with filtration, such as better-performing filters in HVAC systems, require careful consideration from a policy standpoint and can help to minimize potential negative effects on indoor air quality,” said Gentner. This could help to improve indoor air quality even further, preventing even more premature deaths.
Making buildings more energy-efficient can help us move toward a more environmentally safe future. Going forward, individuals also have an opportunity to consider how personal housing choices can affect air pollution. By choosing a more environmentally sustainable option of housing, for example, thousands of premature deaths may be avoided each year. “This study provides guidance to policymakers who are trying to understand what it would mean to have intensive energy efficiency improvements. It tells us what the benefits could be, but also what additional efforts are needed to achieve the benefits,” said Gillingham.
To address climate change, we must pay close attention to the impacts of air pollution. This requires considering emissions from a variety of sources. Whether it is through improving building efficiency, reducing air pollution emissions, or changing personal choices, each of us has a role to play. A tremendous amount of work remains to be done, but scientists like Gentner and Gillingham are using what they know to combat climate change by initiating conversations that could lead to policy changes.
K. T. Gillington., P. Huang., C. Buehler., J. Peccia., , D. R. Gentner. (2021, August 20). The climate and health benefits from Intensive Building Energy Efficiency Improvements. Science Advances. Retrieved November 6, 2021, from https://www.science.org/doi/10.1126/sciadv.abg0947.
Xing, Y.-F., Xu, Y.-H., Shi, M.-H., & Lian, Y.-X. (2016, January). The impact of PM2.5 on the human respiratory system. Journal of thoracic disease. Retrieved November 6, 2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740125/.