If your air handling system recirculates air from occupied spaces there is a risk of virus particles spreading througout yoru air system. To prevent spread filtering through return air consider implementing a UVC (UVGI) disinfection system. General guidance via ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers).
For effective disinfection with UVC light a well designed system is key and balances energy use with disinfection effectiveness. The air speed as well as channel/AHU dimensions determine the contact time of the air with the UVC light and this impacts the rate of disinfection.
For existing situation in most cases we recommend the UVpro KM module. An existing channel can be fitted with UVC or replaced as a whole. We use custom software to calculate the disinfection rate (90% to 99,9% per air passage) and required number of UVC lamps.