I manage a commercial building that is only 4 years old. Our HVAC system is one that runs continually, and adjust air flow with dampers that receive a signal from sensors located throughout the building. My staff is continually ill with respiratory issues. They all say this clears up when they are home.
We've had a great deal of trouble with the HVAC system getting it to function properly and now I am concerned that we are not getting fresh air into the building. We are on the top floor with no opening windows or doors, and in reviewing the blue prints for the facility I do not see any air intakes from outside the building.
I have looked over and over above the ceiling and I do not find an air intake from the outside. I know little about this subject so, that is why I elected to reach out here. Should I NOT have fresh air intake from outside the building? It appears I am simply recirculating the air in the building.

Anyone have an answer?

Thanks,