Ventilation and Schools: Three Key Things You Need to Know

This article Updated September 2024

So…COVID, school openings, ventilation, cold climates, what can we do about air quality in closed buildings?

Three key things you need to know:

1. Install/use/measure/verify mechanical ventilation with filtration that can provide 3-6 air changes per hour

2. Control relative humidity to reduce lifespan of virus in aerosols. 

3. Source control (masking) and distancing (room occupancy) cannot be separated from ventilation.

FRESH AIR FLOWS, RELATIVE HUMIDITY, MEASURE THAT STUFF

There’s a lot of noise out there: ‘faster’ air movement = more air changes per hour (ACH) = better dilution/shorter exposure.

Well, yes, assuming you’re starting with a well-designed delivery system that can provide the amount of fresh air required (3 to 6 ACH/room). Duct size, system layout and ventilation equipment capacity dictate this.

All systems need a MERV-13 air filter (but these can impact air flow). Forced air systems recirculate interior air, so that’s why filtration is so very important. Air conditioning setups should also use appropriate air filters to enhance indoor air quality.

Note: ventilation - bringing fresh air inside - is not the same as recirculation of interior air. Air flow measurements need to be taken AFTER recommended filtration is in place. An air quality indicator can help monitor the levels of airborne particulates and filtration performance.

Not all buildings have a forced air system. Canadian energy engineer @DavidElfstrom shared this flow chart from Harvard Healthy Buildings on ventilation.

CAP OCCUPANCY BASED ON FLOOR AREA AND VENTILATION RATES

@DavidElfstrom also suggests capping occupancy on floor area and ventilation. This makes sense. Arbitrary classroom caps (15? 12? Half of what a jurisdiction considers a ‘full’ classroom?) are not useful, because classrooms are different sizes and shapes, with a massive variation in ventilation rates.

Use SCIENCE to tailor the solution to the space, not an arbitrary % reduction of the current teacher to student ratio. Advanced HVAC systems with high-efficiency filters and smart technologies can significantly enhance air cleaning throughout the home.

Controlling Air Quality Means Controlling Relative Humidity

Relative humidity (RH) levels mitigate the success of ventilation because humid air can extend the life of aerosol droplets. Relative humidity levels need to be controlled, both in classrooms and in hallways (think rainy days, wet gear for a few 100 kids, and a closed building with steamed up windows).

The use of air purifiers with HEPA (high efficiency particulate air) filters can also help maintain indoor air quality by effectively cleaning the air.

Here’s a nice infographic that breaks down the process of improving air quality/reducing risk for airborne virus transmission.

https://twitter.com/KashPrime/status/1298282151201447936/photo/1

WHAT ABOUT VENTILATION SYSTEMS THAT DON'T MEASURE UP TO HEPA FILTERS?

Measuring air flows is great, but where systems are found deficient - who’s going to do that work, when are they going to do it, with what budget, to what standard, and what about hazard mitigation (whoops! Who could foresee finding asbestos wrapped ducts/pipes/plaster in old schools, lead paint, etc.)? This is where air conditioning engineers come into play, ensuring that the HVAC system is installed and maintained to the highest standards for optimal performance and air quality.

Adequately sized stand-alone true HEPA filters with a high clean air delivery rate (CADR) should be in every classroom, regardless. They need to be run continuously but can be run at different fan speeds when the classroom is unoccupied. And they need to be maintained to keep the filter's ability to clean the air of dust, smoke, and particulate matter.

Create and Maintain Healthy Indoor Air Quality

When we talk about indoor air quality in building science, there are three primary ways to create and maintain a healthy indoor environment: elimination (source control of air and moisture-borne pollutants), ventilation (dilution of pollutants), and filtration.

Addressing airborne particles is crucial, as HEPA filters can capture 99.97% of particles 0.3 micron in size or larger. While the most penetrating particle size is smaller than that, virus molecules attach themselves to very fine particles, meaning a HEPA filter work to capture airborne pathogens.

Our best chance at creating safe interior spaces is to make the actual spaces as safe as possible:

• Restrict the occupancy based on room area and actual, measured ventilation rates

• Ensure there are HEPA filtration systems in place

• Maintain the system well, including regular filter replacement

• Quiet operation, auto setting and variable fan speed are key factors

• Each room has an air quality sensor

• Control for humidity

• Reinforce the importance of occupant behaviour: distance/PPE, hand washing and room sanitizing

***NOTE: BHE specializes in building science in the residential arena, but the physics of what is going on are the same, regardless of the building.

For deeper dives into #IAQ, #ventilation, #buildingscience, follow these folks:

@DavidElfstrom

@healthyheating

@shellyMBoulder

@CanaryScience

@CathNoakes

@energysmartohio

What's your experience with air cleaning and ventilation in schools?