HVAC Systems Guidance for Safer Schools

When we talk about air pollution, we generally think of the air outside, but with people spending an unprecedented amount of time indoors, there has never been a more fitting juncture to consider the relationship between health and indoor air quality (IAQ).

COVID-19 spreads mainly between people who are in close contact with one another. When indoors, there is less airflow to disperse and dilute viral particles when exhaled, so the risk of spread of COVID-19 to another person nearby is higher than being outdoors.

Before COVID-19 hit, there are few dogged determination to address the importance of IAQ in public places like cinemas, libraries, schools, restaurant, hotel, etc. Schools are on the front lines of this pandemic. Poor ventilation inside schools is extremely prevalent, especially in older buildings.

October 9, 2020, AHRI launched a digital campaign, aimed at helping school systems nationwide improve indoor air quality as a way to make schools safer.

It put forward 5 means to help school administrators or educators to design or upgrade a more reliable school HVAC system.

1. Retaining services from a qualified and certified HVAC provider

According to ASHARE, for larger and more complex HVAC system like built in schools, should retain the services from a qualified design professional, or a certified commissioning provider, or a certified testing, adjusting and balancing service provider. In addition, technicians employed by these companies should be certified by NATE ( North American Technician Excellence) to make sure they’re highly trained, tested, and proficient in HVAC field.

2. Ventilation

As most of air conditioners do not provide any fresh air, but instead recirculated the indoor air and cooling down the temperature. However, dilution of contaminants, including infectious aerosols, by outdoor air ventilation is an integral IAQ strategy in ASHRAE Standard 62.1. Study have shown that even minimum levels of outdoor air ventilation could reduce transmission of the flu to an extent normally associated with a 50- to 60-percent vaccination rate, making infection less likely.

3.Upgrading filters

The term used to describe mechanical filter efficiency is MERV(Minimum Efficiency Reporting Value), the higher the MERV grade, the higher the filtration efficiency. ASHRAE recommended that the HVAC systems at school should adopts the filter efficiency be at least MERV 13 and perferably MERV14 to better mitigate the transmission of infectious aerosols. But currently, most of HVAC systems only equipped with MERV 6-8, higher efficiency filters require greater air pressures to drive or force air through the filter, so care must be taken when increasing the filter efficiency in an HVAC system to verify that the capacity of the HVAC system is sufficient to accommodate the better filters without adversely affecting the system’s ability to maintain the building’s required indoor temperature and humidity conditions and space pressure relationships. A qualified HVAC technician has the tools to determine the maximum possible MERV filter for an individual system.

 4.UV light treatment

The ultraviolet germicidal irradiation(UVGI) is the use UV energy to kill or inactivate viral, bacterial, and fungal species. The electromagnetic radiation of UV has a wavelength shorter than that of visible light.  

In 1936, Hart successfully used UVGI to disinfect air in Duke University hospital operating room by showing a reduction in surgical wound infectious.

A landmark study during the measles epidemic of 1941-1942 showed a significant reduction in infection among Philadelphia school children in classrooms where UVGI system were installed, compared to control classrooms without UVGI.

UV disinfection systems for HVAC complement conventional filtration, Aaron Engel, indoor air quality equipment manufacturer of FRESH-Aire UV said, by addressing microorganisms that are small enough to pass through filters.

As noted in the AHRI paper, UV light treatment can be used as a supplement to filtration, killing pathogens that escape.

5. Humidity Control

According to an experiment published on PLOS ONE journal on High Humidity Leads to Loss of Infectious Influenza Virus from Simulated Coughs, the result shows that total virus collected for 60 minutes retained 70.6–77.3% infectivity at relative humidity ≤23% but only 14.6–22.2% at relative humidity ≥43%.

In conclusion, viruses are least viable in buildings with humidity between 40- and 60-percent. Schools in cooler climates are susceptible to humidity levels lower than optimal, making humidifiers a necessity.

As long as COVID-19 pandemic is in the community and there is no vaccine, there will never be zero risk for the virus in schools. The likelihood of virus spread still exists, hence, the mitigation measures must be taken.

In addition to practicing social, physical distancing among students and staff, practicing good hand hygiene, using masks, and maintaining a healthy environment, as is the case in schools around the world, a well installed, high efficient HVAC system, with adequate airflow, concerted with UV light equipment and humidity controller would definitely improve the comfort and safety of a building, improve students’ learning efficiency.

Parents want their children to come home safely and in the same physical condition when they are loaded to schools in the first place.



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Bibliography of Citations


e ASHRAE COVID-19 Preparedness Resources website



Post time: Nov-01-2020