Energy Smart Compliance with ASHRAE Standard 241 for Control of Infectious Aerosol

In May of this year the Centers for Disease Control and Prevention (CDC) updated their ventilation guidance for pandemics. Then, in June ASHRAE published Standard 241, its new code-enforceable standard for Control of Infectious Aerosols. While the CDC recommends at least 5 air changes per hour (ACH) of clean air and ASHRAE recommends a minimum Equivalent Clean Airflow rate for infection (ECAi) per person, what is notable about both documents is that they reflect a marked shift in emphasis from prior guidance, which recommended more outside air, to new guidance focused on minimum amounts of clean air. Both the CDC and ASHRAE now also clearly state that clean air targets can be achieved through combinations of outside air, filtration, and air cleaning technologies interchangeably and in combination. 

Whether you plan to follow CDC guidance or ASHRAE’s new standard, the question you should be asking is, “What is the most energy-efficient and cost-effective way to achieve clean air targets?” 

An article in the September issue of the ASHRAE Journal answers just this question. The article, which is called “Why Equivalent Clean Airflow Doesn’t Have to be Expensive”, discusses the cost and energy/carbon implications of different ventilation strategies to comply with Standard 241 and the latest CDC guidance. The findings are based on detailed energy model simulations that look at the energy and carbon impacts of outdoor air ventilation vs. hybrid strategies that combine outdoor air ventilation with air cleaning to meet Standard 241 ECAi and CDC ACH targets.  

The key takeaway is that, in many climate zones, the lowest cost, most energy-efficient way to comply with Standard 241 and CDC guidance is to use the IAQ Procedure (IAQP) in Standard 62.1 for pre-requisite minimum ventilation rates and then add MERV 13 filters to control particles and pathogens and gas-phase air cleaning like Sorbent Ventilation Technology^® (SVT^®) to control gaseous contaminants. 

These key findings are summarized in Figure 2 and Table 3 of the ASHRAE Journal article, which are replicated below. 

The top charts in Figure 2 show that NO ventilation strategy (even the Ventilation Rate Procedure or VRP + 50%) complies with the Standard 241 ECAi target with MERV 7 filters and the bottom charts in Figure 2 show that ALL ventilation strategies including the IAQP/SVT comply with the Standard 241 ECAi target when MERV 13 filters are used. Figure 2 also shows that the most energy-efficient ventilation strategies use MERV 13 and the IAQP/SVT. This is shown for climate zones 5A (Northeast) and 2A (Southeast), but this also applies to all climate zones. To meet the ECAi target for a secondary school in any climate zone with outdoor air and MERV 7 only, outdoor air would need to be increased by at least 2.6 times (62.1-2022 VRP + 160%). This is a clear illustration of the benefit of air cleaning vs. more outside air to deliver clean indoor air for occupants.  

Similarly, Table 3 shows that the lowest cost to operate and lowest carbon strategy to comply with Standard 241 is MERV 13 with IAQP/SVT and energy recovery ventilation (ERV). The lowest cost to install strategy to comply with Standard 241 is MERV 13 with just the IAQP. The numbers in Table 3 apply to climate zone 5A (Northeast), and the result is the same in all climate zones only with less of a differential from baseline in milder, drier climates.

There are many benefits to using the IAQP rather than the alternative VRP to meet IAQ targets both in normal conditions and during pandemics. These benefits include smaller and less expensive new HVAC systems, lower energy use and carbon emissions from less conditioning of outside air, lower operating expenses from less energy use and lower peak demand, and increased resilience to polluted outside air. 

In addition to meeting the CDC guidelines and ASHRAE 241 standard, it is also possible to achieve LEED points using the IAQP with the new LEED pilot credit EQpc165. You can read about this new LEED pilot credit in a recent blog post by my colleague Ryan Peters.  

For too long healthy IAQ has been synonymous with increased energy and systems costs. New standards and guidance for healthy IAQ include air cleaning to meet robust targets. With wildfires and other pollution making our outside air unreliable and calls for more energy efficiency and decarbonization discouraging energy-intensive conditioning of outside air, building designs now more than ever need a solution that is cost-effective, energy-efficient and lowers building carbon emissions. 

Learn how Sorbent Ventilation Technology can be used to comply with the updated Standard 62.1-2022 IAQP Procedure.