As the performance of several HVAC systems in buildings are increasingly being evaluated still, the ASHRAE Epidemic Task Force announces updates (on February 1, 2021) its reopening guidance for HVAC systems to greatly help mitigate the transmission of SARS-CoV-2.
“The Building Readiness Guide includes more information and clarifications to aid designers and commissioning providers in performing pre- or post-occupancy flush calculations to lessen enough time and energy to clear spaces of contaminants between occupancy periods,” said Wade Conlan, ASHRAE Epidemic Task Force Building Readiness team lead. “New information includes the idea behind the usage of equivalent outdoor air supply, way for calculating the performance of air and filters cleaners in series, and filter droplet nuclei efficiency that help measure the systems’ capability to flush the building.”
Major updates to the building readiness guidance are the following:
Pre- OR Post- Flushing Strategy Methodology: The strategy has been updated to add the usage of filter droplet nuclei efficiency, that is the entire efficiency of filter predicated on viable virus particle sizes in the new air, to aid in determining the impact of the filter on the recirculated air on the same outdoor air. This enables the filter efficiency as a function of particle sized, using on ASHRAE Standard 52.2 test outcomes, to be estimated in line with the expected size distribution of virus-containing particles in the new air. This calculation happens to be predicated on Influenza A data and you will be updated as peer-reviewed research becomes designed for the distribution of particle sizes which contain a viable SARS-CoB-2 virus. Additionally, a chart put into help determine enough time to attain 90%, 95%, or 99% contaminant reduction if the same outdoor air changes each hour is known.
Flushing Time Calculator: There’s now a web link to a view-only Google Sheet that may be downloaded for use, to greatly help determine the available equivalent outdoor air time and changes to execute the flush. This sheet is dependant on an average mixed air AHU with filters, cooling coil, with prospect of in AHU air cleanser (UVC is noted in the example), and in-room air cleaning devices. Provided efficiencies of MERV rated filters derive from the performance of over 200 actual filters from MERV 4 through 16, however the tool allows users to enter custom characteristics for specific filters also.
This sheet also calculates the filter droplet nuclei efficiency in line with the cited research but allows a user to regulate the anticipated distribution of virus as desired. In addition, it allows specification of the zone (room) air distribution effectiveness from ASHRAE Standard 62.1 to take into account the impact of the HVAC system air delivery method on the amount of mixing. Default calculations assume perfect mixing. Finally, the tool permits the mark air changes to be adjusted if an owner really wants to achieve another percent removal instead of the recommended 95%.
Heating Season Guidance: The guide now includes data to take into account for heating of outdoor air and the potential effect on pre-heat coils in systems.
Adjustments to Align with Core Recommendations: The Core Recommendations were released within the last month which guidance document would have to be updated to make sure that the info provided aligned with the intent of these recommendations. This included minimum outdoor air supply and filter efficiency requirements and their role within an equivalent outdoor air supply-based risk mitigation strategy.
The guidance still addresses the tactical systems and commissioning analysis had a need to create a Building Readiness Plan, increased filtration, air cleaning strategies, plumbing and domestic water systems, and overall improvements to a operational systems capability to mitigate virus transmission.
To view the entire ASHRAE Building Readiness guide along with other COVID-19 resources, visit ashrae.org/COVID-19.