Ask the Experts: Dr. Bill Bahnfleth, PSU Professor and ASHRAE Fellow

In this installment of enVerid’s Ask the Experts blog series, I catch up with Dr. Bill Bahnfleth, professor in the Department of Architectural Engineering at The Pennsylvania State University and Fellow of ASHRAE, the American Society of Mechanical Engineers, and the International Society for IAQ and Climate.

Bill’s research activities over the past 25 years have focused on indoor air quality (IAQ) and energy efficient HVAC systems. Bill is also active in ASHRAE having served as Society President in 2013-2014, chair of the ASHRAE Epidemic Task Force during COVID, and now chair of the committee that developed the recently published Standard 241 Control of Infectious Aerosols.

Bill and I caught up to talk about COVID, climate change, and carbon emissions and how IAQ and ventilation standards are evolving to keep up with market needs.

CW: You recently gave a talk where you discussed the need for a new IAQ paradigm. What did you mean by that?

BB: The days of optimizing building design and operation for energy efficiency with minimum air quality as a constraint are over. We need to embrace a new paradigm that simultaneously deals with wellness and sustainability as well as resiliency. The key to achieving this new paradigm is looking at alternatives to outdoor air, which is often expensive to condition and may be polluted. These alternatives include high efficiency filtration for particulates, sorption technologies for gases, and technologies like germicidal UV for pathogens.

The good news is that we don’t have to wait for a new silver bullet to realize this new paradigm. Updated standards and technology available today can help us realize this new paradigm now.

CW: Moving away from the paradigm where “dilution is the solution to pollution” is a big shift. Why do we need to make this shift?

BB: The only way we are going to have better IAQ without blowing our energy budgets is to use alternatives to outdoor air, which requires a lot of energy to condition relative to other air quality control technologies.

The other issue with the dilution ventilation approach is that outdoor air is often not fresh air. This has been true for a long time in some urban areas but can happen almost anywhere as wildfires become more common. According to the American Lung Association, 36% of Americans live in places with failing grades for outdoor air quality based on their PM_2.5,PM₁₀ and ozone levels.

CW: If dilution is no longer the best solution, how should we design buildings to simultaneously achieve wellness, sustainability, and resiliency goals?

BB: An approach that utilizes filtration and air cleaning to limit the necessary flow rate of outdoor air is the way forward. You’ve called this the “clean first” approach in your Sustainable IAQ white paper. Designing a building to use air cleaning and energy recovery on a reduced volume of outside air to achieve IAQ goals is far superior from an energy and IAQ standpoint to designing to higher ventilation rates to achieve IAQ goals with limited or no air cleaning.

CW: You mentioned that technology available today can help us realize this new paradigm now. What are those technologies?  

BB: We have the technology to implement a clean first approach now. The key is to use a layered approach to clean indoor air. The layered approach is important because to maintain IAQ targets, we must control airborne particles, pathogens, and harmful gaseous contaminants, and no one technology can do all three. One approach based on established technology is to use high efficiency filters, perhaps MERV 13 or better, to control particles and pathogens and sorbent filtration to control gaseous contaminants. If further protection is needed, one can add germicidal UV to deactivate pathogens.

This layered approach was a key aspect of ASHRAE’s guidance during COVID and has now also been adopted by the Centers for Disease Control and many other organizations.

CW: Let’s talk about how ASHRAE standards are evolving to support this layered, clean first approach.

BB: ASHRAE is doing many things that will enable better IAQ more sustainably in buildings. For example, ASHRAE 62.1-2022 was updated recently to simplify and clarify the Indoor Air Quality Procedure – IAQP for short – and better define requirements for air cleaning systems. Resilience has now also been addressed by the recently published Standard 241, Control for Infectious Aerosol Control. Guideline 44 to address wildfire smoke is also coming along to help with resilience.

CW:  Standard 241 seems to have been written with the paradigm shift you described in mind. Is that right?

BB: Yes, Standard 241 is based on the concept of equivalent clean air delivery rather than outdoor air delivery. In fact, Standard 241 says nothing about outdoor airflows beyond requiring compliance with the applicable ventilation standard for the building type (ASHRAE 62.1, 62.2, or ASHRAE/ASHE 170 or equivalent). Standard 241 simply prescribes minimum flow rates of clean air per person and explicitly states that clean air flow rates can be achieved with code minimum outside air, additional outdoor air, and cleaned indoor air. This gives the designer or operator the freedom to choose the package of options that is most energy efficient and cost effective without compromising IAQ – specifically, airborne infection risk reduction in the case of Standard 241.

CW: Do the recent updates to Standard 62.1 also align with this paradigm shift?  

BB: Yes, the updates to the Standard 62.1 IAQP make it easier for proven air cleaning technologies to offset a portion of the outside airflow required by the prescriptive Ventilation Rate Procedure with cleaned indoor air. The Ventilation Rate Procedure bases outdoor air requirements on space type, number of occupants, and floor area, and not on achieved contaminant levels. Thus, the updated IAQP further enables a layered, clean first approach.

By the way, proven technologies are those for which consensus test procedures for effectiveness and safety exist, for example, sorbents, which can be tested to ASHRAE Standard 145.2, the Laboratory Test Method for Assessing the Performance of Gas-Phase Air-Cleaning Systems.

I will add that until these recent updates were published, I viewed the IAQP very skeptically. This is because the old IAQP required the designer to be an IAQ expert, making it their responsibility to identify the contaminants of concern for a given facility and show that they achieved acceptable levels of each. The perceived liability associated with implementing the IAQP was a strong disincentive to use it.

I believe that the updated IAQP does much to address these challenges by specifying 15 contaminants and acceptable levels for each contaminant. Now all designers have to do is design to the prescribed list of contaminants and measure compliance. This puts the IAQP on a footing that doesn’t have materially different liability from following the Ventilation Rate Procedure.

Additionally, the IAQP now also includes requirements for air cleaner testing. Prior to 2022, Standard 62.1 simply said that air cleaners shouldn’t produce too much ozone. Now the standard includes specific requirements for particulates and gases that making the use of air cleaning more acceptable.

In my view, it is standard updates like these and the new Standard 241 that will enable the new paradigm that simultaneously deals with wellness, sustainability, and resiliency. This is the future.

Learn more in our white paper How to Achieve Sustainable Indoor Air Quality: A Roadmap to Simultaneously Improving Indoor Air Quality and Meeting Building Decarbonization and Climate Resiliency Goals