School Reopening Requires Ventilation Improvement and Monitoring
School Re-opening and Ventilation Standards
Opening schools raise a variety of issues regarding when students can safely return and what measures should be taken to monitor their health. The preponderance of discussions regarding measures to safeguard students have centered on operational controls e.g. safe distancing, masks, disinfecting surfaces and how to monitor compliance with these measures. Less attention has been given to the monitoring of the classroom indoor air quality.
Evidence suggests that CoVID can be transmitted via aerosols for which such operational controls are not as effective. Recently, a number of scientists petitioned the World Health Organization in their belief that there is credible evidence that aerosols ( droplets that remain infectious when suspended in air over long distance) are a significant mode of transmission. (Morawska, Environment International Volume 139, June 2020, 10573). Reducing aerosol transmission in schools requires controls that improve and monitor ventilation in school buildings.
The U.S. Government Accountability Office reported in June that to prevent the spread of the coronavirus inside schools, more than 41 percent of school districts need to update or replace their heating, ventilation, and air conditioning systems (HVAC) in at least half of their buildings.
A National Education Association (NEA) report ( School Ventilation Must Be Addressed in Reopening Plans) listed the types of mechanical problems that lead to poor ventilation. "Fresh air vents were blocked with insulation or plant debris, classroom exhaust fans had defective motors and controls, zone valves were removed or defective, and fresh air dampers that allow outside air in to circulate had been disconnected or were defective."
NEA and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Recommended Actions
The NEA report goes on to recommend steps to improve school ventilation. Recommendations include:.
Increase fresh outdoor air by opening windows and doors when weather conditions allow
Disable demand-controlled ventilation (DCV) controls that reduce air supply based on occupancy or temperature during occupied hours.
Further open minimum outdoor air dampers to reduce or eliminate HVAC air recirculation.
Ensure restroom exhaust fans are functional and operating at full capacity when the school is occupied.
In their recommendations for school ventilation (Reopening Schools and Universities) ASHRAE makes several additional recommendations regarding the inspection of school HVAC Systems:
Before re-opening, make a review of existing spaces (look for covered diffusers, blocked return grilles, overly closed supply diffusers/registers)
Verify proper separation between outdoor air intakes and exhaust discharge outlets to prevent/limit re-entrainment or “short-circuiting” of potentially contaminated exhaust air.
Consider having airflows and building pressurization measured/balanced.
Verify filters match manufacturer’s specifications.
Real time Monitoring Controls Are Needed
Inspection and enhancement of ventilation systems in schools is an important component of a COVID safety program, but is not sufficient to respond to the Covid crisis. Real time ventilation monitoring system controls are needed. NEA reporting indicates that ventilation systems will degrade over time in unpreditable ways. Continued monitoring of HVAC system performance is all too often overlooked. The second reason for the need for real time monitoring relates to the variation in air quality and virus transmissibility. In a study of the concentration levels of CO2 in schools (which will be taken here as a surrogate for air exchange rates and virus transmissibility) a significant variation was found between the median and maximum concentrations.
Variation of average carbon dioxide rates in occupied schools as an estimate of ventilation sufficiency
Such variation could be due to occupancy rates, differences in HVAC systems capacities, “tightness” in buildings due to efforts to save energy, or weather conditions. To ensure proper evacuation of aerosols under different conditions, real time data must be easily accessible so that the proper control of indoor air quality can be maintained. Fortunately there are now available relatively inexpensive ioT based HVAC monitoring devices that allow real time monitoring of CO2, air exchange rates and other critical factors so that aerosols can be diluted to safer levels. (The Internet of Things, ioT, is any system of monitoring and digital devices capable of collecting and transmitting data to the internet.)
Major vendors such as Johnson Controls, IBM, Honeywell, Niagara or Viconics market a variety of relatively inexpensive ioT monitoring devices. The operation of an ioT based systems to control aerosol concentrations is a significant tool that informatics can contribute to the safe reopening of schools. HVAC ioT based systems controls provides a higher safety standard than present HVAC monitoring practices that wait for a complaint to determine that comfort indices are not attained or use periodic audits to estimate air exchange rates.
Employing ioT monitoring still requires as essential all the actions advocated by ASHRAE. However, If a real time monitoring system is installed in the school, data from such a system could alert its administration to any localized problems that require immediate attention. For instance, occasionally larger crowds in an auditorium may trigger an automatic powering up of a ceiling exhaust fan.
The expense of such ioT systems is not prohibitive. The design of an effective system requires defining homogeneous areas of the school from a ventilation viewpoint. A representative sample of similar rooms e.g. classrooms may be used to reduce the number of monitors needed. Special attention should be given to areas in which a large number of students congregate or where ventilation may be restricted. The technology and expertise exists.
Borrowing from healthy buildings’ approaches applied in progressive schools all over the country, administrators can no longer wait for rising indoor air quality complaints to prevent conditions conducive to COVID contagion. They must initiate efforts to prevent excess contagion risk with monitoring plans based upon rapid changes in both HVAC system maintenance status and occupancy levels. The use of such ioT system controls is a small price to pay for protecting the country’s students.
