How to Achieve Sustainable Indoor Air Quality in the Age of COVID-19

We have known for decades that poor indoor air quality is related to increases in respiratory illnesses and sick leave, productivity losses, and lower employee retention and student test scores. Unfortunately, it took a pandemic to instigate an indoor air revolution where indoor environmental quality is viewed as an essential element of ESG (Environmental, Social, Governance) initiatives.

At the same time, the climate crisis is accelerating the green building movement. Buildings are responsible for 40% of global carbon emissions, and HVAC systems account for 36% of commercial building energy intensity. The COVID-19 pandemic only made things worse: as buildings increased ventilation rates, energy use also increased. Thus, the COVID-19 pandemic has refocused the age-old tension between improving indoor air quality (IAQ) and energy efficiency.

The good news is that we can accomplish both indoor air quality and energy efficiency goals by cleaning indoor air before increasing ventilation rates. We call this Sustainable IAQ, and the way to achieve Sustainable IAQ is through proven, efficient air cleaning of particles and gases in buildings.

Initial COVID-19 guidance from ASHRAE and other experts recommended maximizing outside air to decrease the risk of airborne transmission. As William Bahnfleth, professor of architectural engineering at Penn State University and chair of ASHRAE’s Epidemic Taskforce, recently told The Atlantic, the pushback to this guidance was an immediate concern about surging energy usage.

This pushback led ASHRAE to use risk models such as the Wells-Riley equation to compare different risk mitigation strategies for COVID-19. Based on this analysis, ASHRAE and other experts have embraced an “equivalent outdoor air” approach to mitigating the airborne transmission of COVID-19. As Dr. Bahnfleth said during a webinar in October of 2020, “the ongoing assessment of the guidance, including consideration of equivalent outdoor air approaches, has led ASHRAE to conclude that high-efficiency filtration can be as effective and lower cost than ventilation and often more feasible technically.”

In January 2021 ASHRAE announced new COVID-19 guidance based on the concept “that ventilation, filtration and air cleaners can be combined flexibly to achieve exposure reduction goals….” The Core Recommendations, which were updated in October 2021, advise at least minimum outdoor airflow rates for ventilation as specified by applicable codes and standards and a combination of filters and air cleaners that achieve MERV 13 or better levels of performance for recirculated air. According to the Core Recommendations, designers and building operators should “select control options, including standalone filters and air cleaners, that provide desired exposure reduction while minimizing associated energy penalties.”

Building on ASHRAE’s Core Recommendations, enVerid’s Sustainable IAQ framework combines filtration and outside air ventilation to achieve IAQ goals energy efficiently and cost effectively.

There are four steps to design and operate buildings to achieve Sustainable IAQ.

Step 1 is to define indoor air quality goals. Many buildings have not taken this basic step, but we expect this to change going forward as more buildings focus on health and wellness and adopt IAQ goals based on guidelines from ASHRAE, LEED, WELL, and the Harvard School of Public Health. IAQ goals may be stated in terms of CO₂ (carbon dioxide), VOC (volatile organic compound), or PM (particulate matter) levels. With COVID-19, we have seen an increased focus on equivalent air changes per hour (eACH), which considers the combined effectiveness of air cleaning and outside air ventilation to address the airborne transmission of bioaerosols. Click here to read more about the use of eACH to reduce COVID-19 transmission.

Step 2 is to maximize the amount of air cleaning for recirculated air. Tried and true air cleaning technologies include high efficiency filters for particulate matter and bioaerosols (high MERV and HEPA filters) and high efficiency sorbent filters for gaseous contaminants including CO₂, VOCs, and ozone. According to ASHRAE, properly installed and maintained MERV 13 filters are 89.93% efficient for airborne droplet nuclei the size of SARS-CoV-2.^[1] enVerid’s sorbent filters have very high removal efficiencies for contaminants such as CO_2, formaldehyde (a common VOC in buildings), and ozone.

Once we have cleaned as much of the indoor air as possible, Step 3 is to determine how much outside air is needed in addition to the cleaned indoor air to achieve IAQ targets and maintain building pressure. This can be done using ASHRAE’s IAQ Procedure within Standard 62.1, which is a performance-based ventilation design method to calculate minimum ventilation rates accounting for the effectiveness of air cleaning systems. Recent updates to the ASHRAE 62.1 User’s Manual and IAQP calculator tools make applying the IAQ Procedure very straightforward. You can read more about these updates and tools here.

Finally, Step 4 is to validate, monitor, and control IAQ to ensure targets are maintained. IAQ design strategies should be field validated to confirm design targets are achieved in operation. For existing buildings, a baseline IAQ assessment is a good place to start. Implementing ongoing IAQ monitoring is also recommended to give building operators the ability to adapt to changing air quality both inside and outside. Ideally, IAQ monitoring is integrated with building control systems to automate and optimize air cleaning and outside air ventilation for resiliency and efficiency. For example, during wildfire season buildings may reduce outside air and rely more heavily on cleaned indoor air. We recommend buildings deploy RESET-certified sensors, which are readily available from any number of vendors. RESET Air is the world’s first performance-driven data standard and certification program for air quality monitoring for the built environment.

To quantify the benefits of a Sustainable IAQ approach, enVerid developed an open-source COVID-19 Energy Estimator tool to calculate energy, costs and carbon impacts of various HVAC strategies for mitigating airborne transmission of COVID-19. The example below for a 600,000 ft² low-rise office building in metro-Boston shows that minimum outside air per Standard 62.1 IAQ Procedure combined with high efficiency particle filters for COVID-19 mitigation and sorbent filters to control gaseous contaminants delivers comparable equivalent air changes as an increased ventilation scenario (5.25 vs. 5.45 eACH) at less than half the annual operating cost ($121k vs. $255k) and less than a third the annual carbon emissions (98 metric tons vs. 324 metric tons).

To address the dual challenges of airborne pathogens and climate change, we need new ways to achieve safe indoor air quality energy efficiently. Combining filtration and ventilation using the concept of equivalent air changes is the key to low-energy, high-IAQ buildings of the future. Adding ongoing IAQ monitoring and controls provides validation and makes buildings more resilient by allowing them to adapt to changing environmental conditions.

Our personal health and the health of our planet require that we deploy these solutions with urgency to achieve Sustainable IAQ.

^{[1] ASHRAE Epidemic Task Force Building Readiness Guide updated 4/27/21. https://www.ashrae.org/file%20library/technical%20resources/covid-19/ashrae-building-readiness.pdf (pg 42)}

Read the full white paper “How to Achieve Sustainable Indoor Air Quality: A Roadmap to Simultaneously Improving Indoor Air Quality & Meeting Building Decarbonization and Climate Resiliency Goals”or take our free online course for CE credits.