Ensure the IAQ remedy isn’t worse than the problem: Upgrading school ventilation system

By Cara Sloat

When it comes to the COVID-19 pandemic and schools, there has been widespread debate about the risk associated with in-person schooling. Luckily for HVAC professionals, the answer to how to make schools safer is simple: more fresh air.

The pandemic has revealed sobering facts about our existing school building stock: a substantial portion cannot achieve code-compliant ventilation rates, and many have other indoor environmental issues, such as poor classroom temperature control. The research chair of sustainable building technologies at Mohawk College, Tony Cupido found that 30 per cent of Ontario school classrooms are completely unventilated.

This issue has consequences beyond the pandemic. Research in the last two decades has clearly established links between student performance and indoor air quality (IAQ), including showing that providing more fresh air means fewer sick days for teachers and students, and significantly improved task speed when more fresh air is provided. Harvard-based research also demonstrated that CO2, which used to be considered an “indicator” of poor air quality, is itself a contaminant of concern, causing impairment in task orientation, initiative, information utilization and strategy beginning at indoor CO2 levels regularly exceeded in classrooms and boardrooms. Absences due to illness from infectious diseases beyond COVID (colds and flues caught by students in classrooms) also negatively impacts school performance.


Indoor Environmental Quality And Student Performance

Air Quality

  • Carbon Dioxide (CO2)
  • Volatile organics
  • Formaldehyde (HCHO)
  • Ozone (O3)
  • Nitrous Dioxide (NO2)
  • Dust / PM
  • Allergens, including from pests and mould
  • Odours
  • Humidity

Infection Risk

  • Airborne infectious droplets/aerosols
  • Fomites (infectious surfaces)
  • Sewer gas

Acoustic Comfort

  • Noise from HVAC
  • Noise from outdoors
  • Acoustics inside room (echoes)
  • Noise from adjacent Classrooms

Thermal Comfort

  • Too hot
  • Too cold
  • Drafty
  • Radiant discomfort (sun, cold windows)

Light and Views

  • Adequate light levels for reading
  • Avoiding glare
  • Access to daylight
  • Access to views


However, we must make sure that in correcting this problem, we don’t cause more harm to learning outcomes. While adequate ventilation is critical, so are other indoor environmental quality issues:

  • Noise: More than 20 studies have shown a negative relationship between environmental noise exposure and student learning outcomes.
  • Acceptable indoor temperatures: In a 2016 NYC study of 75,000 students, test scores fell by 0.2 per cent for every °1F temp increase: the likelihood of a student failing was 12.3 per cent higher at 90°F then at 75°F.
  • Light and views: research shows clear positive relationships between access to daylight and student performance, social behaviours, and test scores.
  • Finally, the climate change impacts of increasing the energy use of schools will negatively impact learners across the planet, as the number of hot days increase. Therefore, ideally IAQ improvements are implemented as energy- efficiently as possible.

As early as March of 2020, scientific journals had published case studies of HVAC being involved in spreading COVID from one person to another within rooms: a wall-mounted A/C system in Guangzhou China, operated with no fresh air, infected 10 people over the course of a single sit-down meal; an HVAC system spread COVID among call-centre workers only on one side of an open office space.

In response to mounting evidence that COVID is airborne, a number of prominent organizations published COVID response recommendations for schools, which have converged over time on four major IAQ strategies:

  1. Increase outdoor air through the building’s HVAC system. If possible, implement flushing between occupancy periods.
  2. Upgrade to MERV 13 filters in recirculating air handlers.
  3. When weather is good, open windows to increase outdoor airflow. If possible, use fans to force air through the windows.
  4. Install stand-alone high-efficiency particulate (HEPA) air filters in rooms. Since controlled indoor air temperatures, low ambient noise levels, and access to view and windows are important, increasing outdoor air and upgrading filters have been the most popular strategies with school boards.


Maximize benefits

The following suggestions can help maximize benefits as school, or other buildings, consider these retrofits:

When reviewing airflow at existing air handling systems:
  • Consider sealing ductwork. Mohawk College testing and verification saw an average 36 per cent improvement in delivered air flow rates for existing air handlers when fog-type duct air sealer was implemented at buildings for portfolios at five different school boards, with some buildings getting as much as 80 per cent improvements. These changes do not increase energy consumption − but air previously lost to plenum and ceiling spaces is now delivered to classrooms. In fact, median properties saw an eight to 10 per cent energy cost reduction due to better space temperature control. This fogged air sealing product has a 20+ year life expectancy.
  • Implement Controls. It is imperative that systems are off overnight − 62 per cent of heating costs can be avoided if this is done. Demand control using CO2 sensors can further reduce costs by providing fresh air to occupied spaces, and not empty ones.
  • Review the air intake location. Ensure that plumbing vents, natural gas appliance flues, exhaust fans outlets, and sources of vehicle exhaust are far enough away from the intake.
  • Ensure the building is balanced. Increased fresh air supply must be paired with increased exhaust or relief air to keep the building balanced.
If considering a renovation or expenditure to add or improve fresh air capacity:
  • Strongly consider high performance energy recovery ventilators (ERVs). ERVs reduce carbon emissions, minimize peak heating and cooling loads for fresh air conditioning, and provide wintertime humidification for free. For schools, where summertime building use is limited, regenerative dual aluminum core ERVs provide efficiencies of about 87 per cent to 90 per cent, substantially exceeding wheel and fixed plate type exchangers.
  • Learn more about displacement ventilation for classrooms. Displacement ventilation can improve the amount of fresh air in the breathing zone during the winter by up to 33 per cent in a single-storey space, or 46 per cent in a double height space. Research consistently predicts better air quality in classrooms using displacement ventilation. Consider the words of a school board representative after two successful retrofits of schools to displacement ventilation, “The improved air quality is noticeable. It’s dramatically better. And there’s about a 20 per cent savings in energy cost. It’s comparable in cost to a single duct VAV system. Why would you want to do anything else?”
  • Consider induction diffusers and/or destratification fans. Where displacement isn’t an option, ensuring air is well mixed provides the next best thing − induction diffuser tests at Canada’s National Research Council showed a 27 per cent improvement in the amount of fresh air in the breathing zone compared to overhead heated air supply.
  • Consider humidification. Research published by ASHRAE showed that increasing humidity to 40 per cent in the wintertime reduced daycare absence due to illness by 50 per cent.
If addressing filtration:
  • Ensure the filters are not being “bypassed”: visually inspect the filter rack and ensure a tight seal is achieved at all four sides of each filter.
  • Learn the limits of your system: While MERV 13 is the minimum recommended filter efficiency, during an active pandemic, if MERV 14 or 15 can be accommodated without negatively impacting airflow, go for the higher performance.

Installing high performance systems will limit the annual operating cost impact of adding fresh air to a building that previously operated without it. Figure 1 illustrates annual energy costs to ventilate a 27,500 ft2 elementary school located in southwestern Ontario to ASHRAE 62.1-2010 levels before and after energy conservation approaches are considered.

It also shows how a basic fresh air intake at a rooftop unit can be improved to reduce annual energy costs by about 90 per cent compared to the baseline. As contractors and engineers, we have a responsibility to help building owners understand the value of investing in higher performance equipment up front. Supplying adequate amounts of conditioned fresh air will make schools better places to learn even after the pandemic is over: it’s an investment worth making.