Indoor Air Quality at Schools

Indoor Air Quality (IAQ) is increasingly recognized as a critical tool to help address the pandemic. While building code officials, engineers and other industry professionals have considered the importance of healthy IAQ in buildings, the public is now becoming more and more aware that the air we breathe has a major impact on our health. This is especially critical for K-12 schools since they are high-density, occupied spaces with a high degree of intermingling.

This paper will explore the background of IAQ, the fundamentals to ensure good IAQ, and best practices we can utilize to help mitigate the effect of this pandemic. These practices will also help make our buildings more resilient for additional IAQ issues and future pandemics¹.

Some Background

Subconsciously, we all know that proper ventilation, air filtration, and air purification has a major impact on our health and well-being. We have all experienced classrooms with
little to no air flow, and a stale and sometimes odorous scent. Certainly, we feel relief with the simple act of opening a window just “to get air moving.” With regard to contagious viruses, the dynamic of the stale room is no different. By removing these nasty, microscopic particles (which are approximately 500-1,000 times smaller than the diameter of a human hair) from the indoor environment, we reduce the intensity and quantity of the virus and diminish its ability to infect more people.

Our ancestors knew this. In response to the Pandemic of 1918, when over 20,000 New Yorkers died², ventilation was recognized as one of the key attributes to protecting residents from the devastation of the pandemic. According to a recent article in Bloomberg³, New York City officials dictated that building heating systems were to be designed and sized to operate with all the windows open since ventilation was key to purge the virus from indoor spaces.

As the article quotes: Health officials thought (correctly) that fresh air would ward off airborne diseases; then as now, cities rushed to move activities outdoors, from schools to courtrooms. When winter came, the need for fresh air didn’t abate. According to [heating industry expert and author Dan] Holohan’s research, the Board of Health in New York City ordered that windows should remain open to provide ventilation, even in cold weather. In response, engineers began devising heating systems with this extreme use case in mind.

What was true a 100 years ago is true today: viral spread is transmitted from person to person, with air as the most common medium. If you can clean the air by purging with
fresh air, filtration, and/or air cleaning devices, you can reduce the intensity of the viral spread. Reducing the quantity of contagious particles will reduce the intensity of the viral spread.

MIT recently came out with a thought-provoking study, which challenges the “6-foot rule”. The MIT study shows that although proximity to an infected person is important regarding an individual likelihood of contracting the virus, there are several other factors at play. In addition to masking quality and what activity is being performed, the amount of ventilation is also important, especially in the indoor environment. It stands to reason that if contraction of the virus is almost negligible outdoors, to the degree we can make indoor air quality like outdoor air, the less likely we are to have infection contagion within the indoor environment. Simply put, we need to do a better job of making our indoor environment more like our outdoor environment.

The Basics

Building Code requires the provision of fresh air ventilation and filtration of air for buildings with mechanical ventilation. For most K-12 environments, fresh air is provided
by mechanical ventilation. For both pandemic and traditional time periods it is critical that these systems are well maintained. Common issues that we typically find within the K-12 environment include:

  • Mechanical issues such as loose belts and pulleys, dirty ductwork, and control problems limit the amount of fresh air.
  • Broken actuators and dampers reduce the amount of fresh air.
  • Filters that are not installed correctly, not maintained properly, etc. can limit the effectiveness of filtration systems.
  • Ductwork for spaces may create high hazard areas and may expose some occupants to a high dosage of potential infections.
  • Exhaust or return fans not properly working may allow particles to linger within a space for long periods of time.

Certainly, all the above-mentioned issues and any other additional issues are important in preventing high risk environments for our students and staff. To ensure the basics are being incorporated, we recommend a qualified third-party contractor check the design parameters to ensure the mechanical equipment is operating correctly.

Beyond the Basics – A Road to IAQ Excellence

Once the basics are understood and implemented, we can now develop a strategy to attain IAQ excellence. This strategy entails:

  • Incorporating the basics of ventilation and filtration.
  • Air cleaning strategies – developing a strategy which best suits the facility and client needs.
  • Performance Testing – providing baseline and post installation testing. Preferably, perform a test demonstration before a mass installation. It’s best to test and verify performance on a small scale rather than find the system isn’t the correct application after a large investment.
  • Continuous Commissioning – integrating long-term monitoring into the continuous commissioning for the facility.

Further discussions on strategies beyond the basics is discussed on the following pages.

Air Cleaning Strategies

There are several air cleaning strategies available to the end user. The three main airside strategies (HEPA filtration, UV Airside, and Air Ionization) are discussed below.

Bipolar Ionization Technology (BPI)

Bipolar Ionization systems work by producing charged particles which are emitted into the space. Ions have been shown to disrupt the physical and genetic structure of microbes, as well as induce an agglomeration effect on particulates they encounter. For this installation ions are distributed to the space via mechanical ventilation equipment, with the expectation that they will inactivate viruses through the production of hydroxyls. These hydroxyls latch onto viruses and rob them of the necessary hydrogen they need to survive.

This technology is advantageous in two main areas. One, the system installation is quite simple since this coil is typically much smaller than a HEPA filter or UVGI coil and can handle higher air velocities than the typical UVGI coil. And two, since the basis of the system is to generate ionized particles, the BPI system is more effective in neutralizing particles in the space. Other ionization technologies are demonstrably less effective in achieving these results.

We have found that bipolar ionization strategies are effective and efficient in neutralizing particles. However, BPI is not a silver bullet, nor is any solution, and a holistic approach that incorporates an active BPI technology is the best approach. Additionally, the HVAC systems must be in good working order. For the system to work properly the ionized particles must reach the space, which for a duct mounted system is only practical with a functioning system.

HEPA Filtration

HEPA filtration has long been used for high-risk environments, such as hospital operating rooms. HEPA’s can be effective in removing air side contaminants due to the fine mesh nature of the filter, which if designed, constructed, and maintained properly can remove over 99% of particles from the airstream. The ability of the HEPA filter to remove particles will be a function of how well the air is exchanged within a space, measured in air changes per hour, and how well the air distribution pattern is.

For K-12 schools the utilization of centralized HEPA units will be few and far between, since it is highly unlikely that traditional systems can accommodate the physical installation of a HEPA filter. These systems can be quite large and will require extensive ductwork modifications, and the added resistance to airflow will
likely reduce airflow dramatically. Centralized HEPA units are less than optimal since typically existing conditions will require an expensive renovation project, and if not done correctly, can compromise airflow to the space which compromises the IAQ of the space.

  • Placement of the HEPA units within the classroom environment is possible with some success since this strategy offers a low-cost solution with potential quick results. However, if this strategy is implemented, consideration must be given to several factors which may compromise the effectiveness of the unit. These factors include:
  • The performance of the unit will highly depend on users keeping the fans on. This means teachers and staff must monitor the units and buy into their operation. This can be tough to manage and administer in a school environment since teachers typically, and rightfully so, want to maintain control of their classroom.
  • Noise: Local HEPA units can be very noisy. We have observed instances where staff will turn the units off and/or place at a low-speed setting, which totally defeats the purpose the HEPA filter.
  • Placement: Need to be concerned with unintended consequences of introducing air currents into space
  • Maintenance issues: Typically filters need to be replaced at least one or twice a year. Note that since viruses and bacteria are not deactivated in a HEPA filter, the filters need to be changed out by qualified personnel.

Ultraviolet Germicidal Irradiation (UVGI)

UVGI is another technology which has been around for a long time and has had a measure of success. In typical applications, a UVGI coil is added to an air handling unit and/or supply duct, but standalone/portable units are also available. If properly designed, installed, and maintained, the air will sterilize as it passes by the coil.

The main downside of this technology is that it will sterilize only the air which passes across the coil, which makes the system highly dependent on the effectiveness of the air handling and distribution system. Also, this type of system will not sterilize air on surfaces since the particles on surfaces, unless disturbed, will not return to the air handling unit via the ductwork.

Another concern is cost. It has been our experience that for retrofit applications the installation of these units can be expensive, since typically there are spatial issues and the need to make duct modifications. If this option is considered, we recommend that a cost benefit analysis be conducted comparing UVGI to other technologies.

Performance Testing

Clients are being inundated with new technologies, often with conflicting claims. Once getting beyond the basics of proper filtration and ventilation, which is universal for most buildings, we recommend that air cleaning technologies be evaluated with the help of a qualified independent expert. In addition to constructability review and cost estimate, the expert should guide the client in performance testing. The performance test should simply test to verify vendor claims. In general, the following table is a good guide for performance testing.

IAQ Technology

On the following page is a summary of a recent performance test for a downstate New York High School. Trending was completed to test for system performance of above variables. The top photo shows the testing equipment, while the bottom photo shows the results. By conducting the test in a transparent manner, the performance of the equipment can be verified, thus validating that the investment is resulting in tangible benefits.

IAQ Technology

From the above test results one can see that ions are up dramatically, VOCs are reduced (indicator that particles are neutralized), and Ozone is at an acceptable level (at least in zone space). From this data we can see the unit is working as intended with no notable deleterious effects.

Continuous Commissioning

Once the basics of ventilation and filtration are completed, with an indoor air cleaning technology system which has been implemented, tested, and proven to perform, a longterm monitoring plan will help sustain the performance for years to come.

A long-term monitoring plan should follow the following principles:

  1. Leverage existing BMS as much as possible.
  2. Ensure basic variables, such as monitoring filter pressure drop, total airflow, and outdoor air flow, as a first step.
  3. Set up reporting which is simple to understand.
  4. Focus on primary variables. For example, if the intent is to limit particles and maximize ions, such as through BPI technology, then these are the two variables you want to monitor and trend.

Data should be easily retrievable and reported on a consistent basis, with designated personnel responsible for these tasks. Fifteen minute or hourly intervals are typically acceptable. If problems can be identified and fixed in a timely manner, then we can maximize the IAQ performance of our buildings and improve the health and well-being of the occupants.


Rebuilding our society after the devastation of the Covid-19 pandemic will take time and significant investment. We as a society will need to utilize several tools to help rebuild a better, more verdant future. Indoor Air Quality is one of the most effective tools to improve our buildings health today, and to help fortify our buildings for future pandemics.

By adopting a pragmatic approach starting with the basics of filtration and ventilation; applying air cleaning technologies, testing performance, and continued monitoring; we can help maximize the benefits of our IAQ investments.

About the Author

Jeremy McDonald, PE, is a Principal at Guth DeConzo Consulting Engineers, PC where he designs, installs, and commissions HVAC systems and IAQ technologies. Mr. McDonald’s previous experience includes serving as an adjunct professor at Rensselaer Polytechnic Institute, where he taught principles of building systems, including IAQ technologies.

¹ Alexander D D, Bailey W H, Perez V, Mitchell M E, Su, S. “Air Ions and Respiratory Function Outcomes: A Comprehensive Review.” Journal of Negative Results in BioMedicine, September 9, 2013; 12, 14. See:

² The 1918 Influenza Epidemic in New York City: A Review of the Public Health Response

³ “Your Old Radiator is a Pandemic fighting Weapon”, Bloomberg City Lab-Patrick Sisson, August 5th, 2021

⁴ Since ozone is a variable of high concern, we recommend the ozone be measured at three locations: Outdoors, at discharge of unit, and in operating space.