At this point in the COVID-19 pandemic, energy and facilities engineers are familiar with ASHRAE's guidelines for mitigating the risk of infection spread. These can be broken down as filtration, mitigation, and dilution. Dilution, or adding additional fresh air, is the best "bang for the buck", especially in facilities that feature a modern Building Automation System. There are a few different sequences of operation that can be implemented by your BAS contractor to dilute the air of recycled air in your facility.
First, many air handler control sequences already use demand control ventilation. This sequence brings in additional outdoor air if the CO2 concentration of the room increases. However, this method may limit infectious aerosol dilution if CO2 concentrations dip after a slight opening of the outdoor air damper.
Another method is to reset the outdoor air damper percentage unless the heating or cooling equipment is unable to keep up with the zone or discharge air demand. This ensures that the maximum possible amount of fresh air is being delivered while still meeting conditioning requirements.
During short periods of unoccupancy, a purge mode can ensure the maximum number of air changes. The BAS contractor can add a program that fully opens the outdoor air damper while closing the return damper, and enabling the relief fan (if a relief fan is present). The contractor can either add a button to the graphics to enable this sequence for a certain time period, or a special purge schedule can be set up if the unoccupied times are known and consistent.
CDC studies suggest that Covid-19 aerosols can remain infectious for up to 16 hours. Thus, consideration should be given to a “morning purge” cycle to work in conjunction with a regular warm-up or cool-down.
New technologies can also be used to lessen the infection risk. For example, Senseware has a patent-pending infectious aerosol sensor currently in beta testing. Once infection risk has reach a critical level, alarms can be sent to building personnel. Through BACnet integration, such a sensor could also trigger a purge cycle.
With a little planning to decide the right course of action for your facility, your existing BAS can mitigate aerosol infection risk according to ASHRAE particulate dilution guidelines. Contact The Stone House Group if you have questions regarding how your BAS can be optimized to safeguard the wellness of occupants.