Controlling Infectious Aerosols: A Guide to Understanding and Applying ASHRAE Standard 241.
Agentis Air company president Larry Rothenberg discussed the recently introduced American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 241 during the August 2023 Healthy Buildings Week, presented by Facilities Management Advisor.
ASHRAE Standard 241 was developed in response to the pandemic, to provide a complete framework for planning, design, operation, and maintenance of systems that reduce the risk of airborne infection transmission.
Previously, ASHRAE indoor air quality standards focused on ventilation and bringing outdoor air into facilities, however the energy cost in doing so is significant.
The new standard “allows for a lot of flexibility, and this flexibility is important because we have a lot of technologies coming on the market. What we saw during COVID is that people want to be able to address this concern in a way that is responsive to the needs of the occupants,” Rothenberg said.
ASHRAE 241 has four key components:
- Infection Risk Management (IRMM)
- Requirements for equivalent clean airflow rate
- Requirements for use of filtration and air cleaning technology
- Planning and commissioning
ASHRAE 241 allows for the use of multiple air cleaning solutions in addition to outdoor air. The equivalent clean air flow per individual (ECAi) can be calculated for the specific density of any shared space and can be achieved through outdoor air, if feasible, but also through recirculated, purified air and air disinfection.
Outside air provides aerosol dilution, with a higher energy expense as the air must be conditioned (heated or cooled) before it can be introduced. Outdoor air may also bring indoors other toxins and allergens.
The alternative air cleaning technologies, including room air purifiers, considered in ASHRAE 241 are well-suited for removal and neutralization of viruses, pathogens, and other ultrafine particles. Unlike outdoor air, these additional tools can support elevated clean airflow goals with lower cost and energy use.