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Mechanical Systems







Improving air quality is a fundamental strategy to mitigate the spread of COVID-19 in school facilities. This guide offers both short and long-term considerations for adapting building Mechanical Systems. Information summarized is from ASHRAE and industry experts.

Airborne transmission is a key driver of COVID-19 spread which raises the air quality of school facilities to an urgent level. While the risk of airborne exposure can’t be eliminated, there are a range of strategies that school leaders can pursue to mitigate its danger inside school facilities. 

The American Society of Heating, Refrigeration and Air-Conditioning (ASHRAE) is leading a national discussion about the practical challenges communities face in strengthening indoor air quality as they prepare for schools to reopen. ASHRAE’s position regarding the relationship of indoor air quality to the spread of COVID-19 is summarized in this statement:

“Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the 

virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures…. Ventilation and filtration provided by (HVAC) systems can reduce the airborne concentration…and thus the risk of transmission through the air.”

ASHRAE’s COVID-19 Epidemic Task Force has released a comprehensive report which includes checklists and other useful tools.

FGMA is working closely with industry leaders and local school district partners to share information, offer guidance and provide connections to “best practice” resources and tools that will help schools be as prepared as possible when they reopen their doors.

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Key terms: Essential, Guidance and for Consideration

At this time, local school districts, college/university leaders, elected/appointed officials, facilities managers, and design professionals are reviewing broad guidelines and roadmap recommendations from a variety of sources. 
It is important to note that many of the recommendations are not mandatory. However, there are a range of recommended strategies that school systems may choose to implement both to protect staff and students and minimize the spread of COVID-19. Typically, recommendations fall into three categories:


Either required by law, policy, or governmental order, OR a critical practice.


Best practices gleaned from research and long-term experience, highly recommended for implementation when feasible.


Additional best practices informed by emerging research, recent studies, and practical experience to be considered for implementation when feasible.

Decision-makers should recognize that recommended guidance may not be feasible in all settings. Education leaders and facility managers should consult local health departments, engineering professionals, and facilities engineers. Some considerations should be based on the needs of each school system, school, and campus as appropriate.

Triton College


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Indoor air quality (IAQ) is the air quality within and around buildings and structures. IAQ is known to affect the health, comfort, and well-being of facility occupants. Poor IAQ has recently been linked to sick building syndrome, impacted productivity, and impaired learning.

Most discussions of mitigating the spread of COVID-19 in schools focus on social distancing. The more people in a given area, the closer they are together and the longer they stay, the greater the risk of infection. 
Improving air quality for people in the building is just as important. The four key strategies that are most prominent today revolve around these themes: Dilution, Filtration, Disinfection.


Building Operation Changes

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Above all, ensure that HVAC systems are properly maintained and filtrated – particularly in buildings that have been closed for a period of time. Without these basic practices, systems will build up mold and particulates that spread respiratory disease.
A well-trod maxim is “the solution to pollution is dilution.” Outside air can dilute toxins circulating in interior spaces. To the extent possible, increase outside air ventilation whether through mechanical or natural means with operable windows. 
Unless outdoor temperatures are too warm, school buildings should be “flushed out” for two hours before and after a building is occupied daily.



Manage Relative Humidity

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Dry air (below 40% relative humidity) can reduce healthy immune system function; potentially increase the transmission of airborne viruses; increase the survival rate of pathogens; and diminish effectiveness of hand hygiene and surface cleaning. For optimum air quality, relative humidity inside schools should be maintained at levels between 
Extensive humidification is both energy intensive, costly, and difficult to retrofit in existing facilities. Experts advise concentrating efforts in select spaces such as areas where groups congregate (corridors, gyms, cafeterias) or spaces that may be especially critical such as Nurse’s Stations and Isolation Rooms.


Capture Airborne Virus Particles

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The fraction of particles removed from air passing through a filter is termed “filter efficiency” and is provided by the Minimum Efficiency Reporting Value known as MERV. The higher the MERV rating (on a scale of 1-16), the greater the efficiency. MERV filters with a rating of 13+ are efficient at capturing airborne viruses with MERV 14 filters preferred.
Even better, are HEPA (High Efficiency Particulate Air) filters which are more effective than MERV 16 filters and can be 99.97% efficient at filtering airborne particulates.



Environmental Disinfection

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There are two primary purification technologies to remove COVID-19 virus particles from the air: 
Ultraviolet Energy (UV-C)        
Bipolar Ionization (BPI)

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There are a range of options for quickly adapting building mechanical systems to improve air quality. Beyond good engineering and maintenance practices to reduce the virus’ spread, an additional benefit that may ease people’s concerns are integrating practices that broadly improve occupant health.

As building operators prepare to re-opening facilities, they can consider these actions:

Conduct a thorough asset inventory of the mechanical system ranging from fans to boilers to pumps

  • Consider reviewing service calls on existing HVAC equipment from the past 6 months.

  • Check building automation systems for alarms, overridden points, or locked points.

  • Consider reviewing troublesome pieces of mechanical equipment.

Test and balance existing ventilation systems to help determine if maintenance is needed to maintain code-compliant air supply rates

Review HVAC Programming and consider flushing sequences or modes to operate the HVAC system with maximum outside airflows

  • Further open minimum outdoor air dampers, as high as 100%, thus increasing the dilution of the return air stream.

    • Consider monitoring systems response to increase of outside airflows. Note that this might impact thermal comfort or humidity and becomes more difficult in extreme weather. Many engineers recommend flushing sequences two hours before and after daily occupancies.

Consider reviewing humidity levels in spaces

Studies show that spaces with a relative humidity (RH) between 40% and 60% can cut the airborne travel distance of viral droplets and reduce the risk of infections.

  • Consider providing local humidification in select spaces for higher risk areas and critical populations.

  • Consider conducting night purges for dehumidification.

  • Review possible impacts of increased humidity (local and holistically to the facility) to existing finishes in spaces, building envelope elements, and the possible increase in energy consumption.

Consider eliminating demand control ventilation (DCV)

Demand controlled ventilation (DCV) is an automatic adjustment of ventilation equipment according to occupant choice. DCV is a control method that modulates the volume exchange of fresh or outside air into an enclosed space by mechanical air conditioning equipment.

Mount Prospect Po...n-Professional (72).

Review and consider, if needed, changing existing filters to MERV 13 or better. Consider adjusting existing filter racks to accommodate change in filters.

  • This possibly allows additional outside air into spaces. Monitoring is required to ensure that this strategy will not cause relative humidity problems.

  • Review possible impacts difference in pressure drop between existing and new filters.

  • Monitor and be prepared as filters may require more frequent replacement to maintain design airflow.

Test and balance existing ventilation systems to help determine if maintenance is needed to maintain code-compliant air supply rates

Take into account existing systems and mechanical units in spaces to determine what Environmental Disinfection strategies can be used.

Ultraviolet Energy (UV-C)

  • Ultraviolet Energy inactivates viral, bacterial, and fungal organisms so they are unable to replicate. While the entire UV spectrum can inactivate microorganisms, UV-C energy is the most effective. The main types of HVAC systems that use UV-C energy include in-duct air disinfection; up-repair disinfection; in-duct surface disinfection; and portable room decontaminators.

  • While UV light (specifically UV-C) has been well studied in infection reduction, no definitive science is available regarding its effect on COVID-19 when applying to an operating mechanical system.

  • There is a good deal of standardization regarding its use with reliable testing methods. The downside is that people can’t occupy a room when it’s being used. Treatments must be scheduled when school buildings are unoccupied.

Bipolar Ionization (BPI)

  • BPI is a recent technology and there are not yet established standards to guide its use.

  • The technology uses an electronic charge to create a plasma field filled with a high concentration of Positive and Negative ions. Together, the ions work to agglomerate fine particles so they can be captured in filters.

  • BPI can be used in occupied spaces at both the system and local level. To date, it’s been primarily used at the system level where it can mitigate biologic growth in cooler systems.

  • In comparison to UV-C which requires a “line of sight” to attack virus particles, BPI ions disperse and find their way within a given space.

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A beneficial outcome of the COVID-19 crisis may be that communities will assess the operational policies and maintenance procedures of schools through a more human-focused lens. This could speed the adoption of facilities practices that promote health and well-being.

In the future, it seems likely that school and community leaders will have a better understanding of the facilities practices that help ensure the health, safety and well-being of students and school staff. It could be that the WELL Building Standard (WELL) approaches are more readily adopted and integrated into long-term strategies to facilitate a healthy and safe workplace or facility for all.
Some of the WELL Building Standards strategies that will guide future facilities designs, policies, and procedures:


Recommends that spaces exceed ASHRAE 62.1-2010 air supply rates by 30-60%.


Recommends increase in media filters are used in the ventilation system to filter outdoor air supplied to occupiable spaces.


Recommends implementing Ultraviolet air treatment and Condensation management.


The built environment has an important role to play in building a healthier, more sustainable communities. This is becoming even more apparent as communities respond to the COVID-19 pandemic.

Balancing health, energy efficiency, and resilience will deliver better buildings that in turn will yield healthier occupants, greater productivity, and more vibrant communities.
Key messages this guide endorses are:

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Decreasing the risk of airborne COVID-19 transmission begins with assessing critical HVAC systems, adapting them wherever possible and beginning to prepare for more long-term strategic decisions that will help school districts, facility managers, and building engineers be better prepared in the future.



FGMA expresses appreciation and gratitude to the following individuals who have contributed to this document and its research.


Dean Manasses, FGMA


Caroline Brogan, FGMA
Haley Kell, FGMA
Joshua Lawrence, FGMA
Kelly McCaffrey, FGMA
Sheila Murphy, FGMA
Brittany Peterson, FGMA
Carol Stolt, FGMA
David Swain, FGMA

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