Engineer HVAC systems with ASHRAE 241 in mind

ASHRAE 241 instructs mechanical engineers about how keep infectious aerosols minimized

By Consulting-Specifying Engineer February 8, 2024
Courtesy: Amara Rozgus, CFE Media and Technology

ASHRAE 241 insights

  • ASHRAE Standard 241, released in July 2023 as an extension of ASHRAE’s epidemic task force, was swiftly brought to market at the White House’s request to establish minimum requirements for controlling infectious aerosols in a building’s air distribution systems.
  • Focused on reducing disease transmission, the standard introduces concepts like equivalent clean air flow and infection risk management mode, the latter being optional unless adopted as code or law in a region, aiming to mitigate the spread of diseases like COVID or flu through the implementation of a building readiness plan (BRP) with specific prerequisites and an extensive assessment process.

Is your engineering team ready to mitigate COVID-19 and other infectious aerosols? While watching the webcast HVAC: IAQ and IEQ is a much more complete overview, reviewing this transcript of the presentation helps define the topic better. It has been edited for length and clarity.

This information was presented by Emmy Riley, CEM, BEAP, WELL Performance Testing Agent, Energy Engineering Team Leader & Account Manager, Cyclone Energy Group, Chicago.

A newer standard that came out in July 2023 is ASHRAE Standard 241: Control of Infectious Aerosols and it came out of the sort of an extension of ASHRAE’s epidemic task force that was active during the COVID pandemic and the standard itself was developed at the request of the White House. And that’s why it got brought to market quickly, faster than other standards that ASHRAE has developed.

The purpose of it is to establish minimum requirements for the control of infectious aerosols. And what we’re trying to do is reduce disease transmission. And this standard is talking about not proximity transmission, it’s talking about in a whole building and its air distribution system. How can we help mitigate that? And it has requirements for outside air system design and it also includes recommendations on air cleaning systems.

Two of the big concepts in the standard are equivalent clean air flow and infection risk management mode. And infection risk management mode, the way the standard is set up is it is like other standards, optional to adopt until unless a region adopts it as code or law.

You would identify an infection risk management mode, like if there were high levels of COVID or flu and you wanted to mitigate the spread of disease in a building, that’s when this would come into place. The deliverable that comes out of using Standard 241 is called a building readiness plan, or a BRP. A prerequisite for using Standard 241 are that you need to also comply with ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality already and you also need to use minimum efficiency reporting values (MERV) 11 filters or better.

There needs to be a level of filtration that is in a typical commercial range. And how you would implement ASHRAE 241 is an extensive process. It has some tools attached to it to calculate a passing or failing score or level for each zone in your building, you would do a space-by-space inventory, have the full heating, ventilation and air conditioning (HVAC) inventory including sensors. You would get testing and balancing done, have commissioning done, have lab testing done.

Then based on the assessment, you would address any deficient areas that don’t meet the standard, the recommendations in the standard. The building readiness plan would be updated annually.