Ventilation Key to Reducing Risk
Adequate indoor ventilation is important in reducing risks associated with COVID-19. Poorly ventilated indoor spaces can lead to increased levels of disease transmission.
Download here the Engineering Control Flow Diagram.
Ways to improve school ventilation
- increase the amount of outdoor air introduced into the building
- improve the filtration of recirculated air
- increase the volume of air exchange per hour
- use supplemental devices such as portable air cleaners and window-mounted box fans. For maximum efficiency, box fans should be pointed outwards, drawing inside air outdoors.
It is important that a school’s heating, ventilation and air conditioning (HVAC) system be commissioned prior to reopening to verify its expected performance. Commissioning will confirm that:
- filters, dampers, as well as economizers seals and frames are intact, clean, functional and responsive to control signals
- temperature and relative sensors are properly calibrated and communicating with the building automation system
- air handling systems are providing sufficient airflow to individual rooms and exhaust fans are functional and venting outdoors.
HVAC Systems Best Practices
- Ventilation systems that use 100% outdoor air eliminate the risk of viral material being recirculated in a building and therefore offer the greatest reduction of risk for indoor disease transmission.
- Filters in a HVAC’s air handling unit are a first line of defense in removing virus germs from recirculated air. High Efficiency Particulate Air (HEPA) filters and Minimum Efficiency Reporting Value (MERV)-rated filters are effective at removing COVID virus aerosols. MERV13 rated filters are recommended as the top risk reduction strategy for COVID-19. Filters should be upgraded to the highest rated filter that can be accommodated by a school’s HVAC system.
- It is critical to ensure an HVAC system’s filter cage is maintained. Any gaps in the housing assembly will impair filter efficiency. Filter changes are recommended after a period of low or no building occupancy (i.e. weekend, holiday). When feasible, filters can be disinfected with a 10% bleach solution or another appropriate disinfectant before removal.
- Increasing the number of air changes per hour (ACH) in an indoor space can also enhance ventilation. ACH should be evaluated for each classroom in relation to the size of the room and occupants’ activities. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has established ventilation standards for different types of school spaces (ASHRAE 62.1 2019 – Ventilation for Acceptable Indoor Air Quality Standards). The amount of air flow into each school room should ideally exceed these minimum standards.
- Extending operation of an HVAC system also helps improve ventilation. It is recommended that a school building’s HVAC system be turned on at least two hours prior to the arrival of staff, teachers and students and remain running at least one hour after all occupants have departed. The system should also be operated at maximum total airflow to the extent possible.
- Using displacement ventilation in classrooms and offices is another effective engineering control that provides enhanced air mixing, moving potential contaminant air away from students and teachers.
- To maintain HVAC operation at maximum air flows independent of the number of students, teachers and administrative staff in the school building, demand-controlled ventilation sequences should be disabled.