Coronavirus Infection Control Part 3

You may be able to alter the settings in Air Handling Units (AHUs) to increase dilution and reduce infection in your facility. Pictured here is an AHU that EEI is re-programming for an archives facility in a state library.

We conclude our Coronavirus infection control series in response to the ASHRAE article with our thoughts on dilution today. We will continue to post on this crucial topic throughout the month. As we all do our part to ‘flatten the curve’ of the coronavirus pandemic, everyone also recognizes the importance of educating ourselves. EEI’s commissioning expertise focuses on optimizing the built environment. We can’t tell you more than you probably already heard, read, or discussed regarding the medical side of coronavirus. However, EEI cares about the health and safety of our staff, clients, and all of you reading this. So, our newsroom will cover pertinent topics regarding infection control, remote monitoring of systems, and engineering advances related to facilities.

ASHRAE Article Explained

Last week, we shared ASHRAE’s article, Guidance for Building Operations During the COVID-19 Pandemic. The article offers quite a few suggestions for coronavirus infection control in facilities. That said, COVID-19 is so new that no one knows very much about it.

Air Dilution

In Part 3 of our series on the ASHRAE article, our staff would like to share our thoughts specific to dilution and airflow. Our experts on healthcare commissioning and indoor air quality researched what we know about the pandemic and put together the following Q&A on the topic.

Dilution: Increase ventilation airflow:

  • Q: How does increasing outside air ventilation remove viruses from indoor air?
  • A:  Outside air from intakes located on the roof and or away from people will have a much lower concentration of virus particles than recirculated air.
  • Q: What should I consider before increasing outside air ventilation level?
  • A1: First, check your systems for the following
    • Air handler cooling and heating capacity. As outside air temperatures get really hot or really cold, the air handler may not be able to heat or cool in some extreme weather conditions.
      • Review building automation system trends (if you have them) from past summer and winter operation. This helps predict the coil entering temperatures that ‘max out’ your coils.
    • Exhaust / Relief Capacity.  Standard Variable Volume Air Handlers designed for 100% outside air economizer should not affect building pressure.  If your system is different, such as Variable Refrigerant Flow with Ventilators, increasing the outside air volume may not be as simple.
  • A2: Second, if you have verified your capacities, take the following steps:
      • Reprogram the air system to automatically back off the outside air amount when cooling or heating is capacity is maxed out.

Dilution: Increase space total airflow:

  • Q: How does increasing total space airflow remove viruses from indoor air?
  • A: By removing and replacing air more frequently. This is likely to be most effective with higher levels of filtration if the air supplied is being re-circulated.
  • Q: What are some ways to increase space total airflow?
    • Where spaces are served by equipment that cycles fans on and off, operate the fan continuously.
    • VAV (variable flow) system measures:
      • Increase minimum airflow setpoints at terminal boxes.
      • Increase max airflow at terminal boxes in areas of greatest concern.
      • Disable unoccupied settings that reduce airflow.
    • VAV (variable flow) system measures, limitations:
      • Hot water system capacity for reheat coils that need to reheat more air. Capacity will limit how much minimum and maximum VAV flows can be increased.
      • Resetting the air handler discharge temperature up reduces reheat and allows greater flow increase. This should be done with programmed or manual oversight to prevent under-cooling of some spaces.
      • Air handler supply fan capacity.

CDC Recommendations

This CDC Infection Control Guidelines page provides a table for estimating the time for contaminant removal.

For example, a typical room with eight air changes of supply air (about 1 CFM per square foot for standard height room) can remove 99.9% of the contaminant in 52 minutes. So, by doubling the airflow from say 4 to 8 air changes, the contaminant removal time is reduced by half from 104 to 52 minutes. This assumes an empty room without people present and generating aerosol particles, but is still informative.

We will continue to post on topics related to coronavirus throughout this month. Please reach out to EEI to ask a question or get a consultation!