Current ventilation guidelines recommend maintaining ventilation with 100% outdoor air 24/7, or as much as possible if that is not feasible, as an effective way to keep airborne pathogen concentration under control. Obviously, outdoor air needs to be filtered and conditioned to guarantee the indoor temperature and humidity set points; this, in turn, implies a higher HVAC-related primary energy consumption, because more outdoor air needs to be conditioned compared to the pre-COVID-19 situation, when the flow of outdoor air was typically 20% of the total supply air entering the space.