ASHRAE Standard 241 Control of Infectious Aerosols

ASHRAE has published a draft of ASHRAE Standard 241 Control of Infectious Aerosols.

It is open for public comment until May 26, 2023.

Publication is expected in July.

Comments on the proposed Standard can be made here

Background

ASHRAE is the a professional society of building mechanical engineers that sets building energy and ventilation standards, among other standards and guidelines.

Most commercial buildings in North America follow ASHRAE standards. Residential buildings tend to follow the IECC standards, which borrow heavily or defer to ASHRAE standards. Many other countries and jurisdictions globally model their codes off of ASHRAE standards and borrow directly from it. I suspect many jurisdictions will adopt Standard 241 as they do other ASHRAE energy and ventilation standards.

The ASHRAE Standard Project Committee 241P is chaired by William Bahnfleth, Ph.D., P.E., whose name should be familiar to those who were following the research on COVID-19 aerosol transfer.

Ventilation standards have always considered the health of occupants, but with a focus on chronic air pollutants, not exposure to airborne infectious diseases. This a new standard aimed to given guidance to buildings specifically with airborne infectious disease transfer in mind.

ASHRAE Standard 241 makes several improvements beyond outdoor air ventilation:

• effective ventilation rates are roughly double for key spaces like offices and classrooms
• allows air cleaners to contribute to the ventilation requirement
• sets minimum requirements for maintenance and filter replacement, which has been perhaps the main challenge to mitigation systems

I suspect many buildings will comply with the standard with permanent or semi-permanent air cleaners, rather than increasing the outdoor air ventilation rate.

Increasing the outdoor air ventilation rate is costly, as heating and cooling outdoor air is the primary contributor to heating and cooling loads in commercial buildings (see this report by my colleagues).

What does this mean for those working on building-level infectious disease transfer mitigation?

I doubt EAs can contribute to the science of air cleaning devices or research around infectious disease transfer as it relates to the standard unless they've been working directly on that for some time in an academic or industry capacity. EAs have tended to bring optimism but show a significant lack of expertise, as evidenced by the misplaced fervor around UV-C as a mitigation technology.

There are several things that EAs can help with:

• Ensure ASHRAE Standard 241 gets adopted by jurisdictions. This could look like writing to your city, county, or state code office and requesting that new or existing buildings to follow Standard 241.
• Help schools apply for grants to comply with Standard 241 There are billions of dollars available for schools, colleges, and universities to improve their buildings to reduce airborne infectious disease transfer. However, most schools lack the staff or expertise to apply for funding and carry out these projects. Unfortunately, there are a lot of hucksters looking to take advantage of the funds and sell systems that simply don't work, or don't adequately reduce airborne transfer compared to the best mitigation options.