How a school in Chiang Mai successfully combats AQI and Covid-19
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How a school in Chiang Mai successfully combats AQI and Covid-19

Prem Tinsulanonda International School in Chiang Mai puts student health and safety first to achieve extremely low AQI and COVID-19 transmission risks in its classrooms.

To reduce the transmission risk of COVID-19, a high ventilation rate of outside air is crucial in order to flush out airborne particles that could carry the COVID-19 virus. A good indicator of adequate ventilation rates is the indoor CO2 value. Outside air has a CO2 level of approximately 400 ppm but indoor air, especially in unventilated classrooms, can quickly reach very high levels.

Most centres of disease control recommend CO2 levels in classrooms to be below 800-1000 ppm, The German UBS (Environmental Protection Agency), for example, states below 1000 ppm. The US CDC (Center for Disease Control) goes even further and recommends CO2 levels for classrooms below 800 ppm to minimise the COVID-19 transmission risks.

Unfortunately, the vast majority of classrooms in schools do not have active ventilation systems. With many children in a room, CO2 often exceeds 3000 ppm. As a result aerosols with potential COVID-19 viruses circulate in the classrooms and pose high infection risks, similar to the latest outbreak seen in pubs.

Beyond COVID-19 transmission risk, high CO2 levels also impact cognitive performance and hinder learning, with some studies showing a 50% decline, with CO2 already at 1400 ppm.

In 2019, Prem became serious about wanting to know more about the indoor air quality its students experience in the classrooms. Particular attention was paid to the indoor PM2.5 values during the Northern Thailand smoky season, and levels of CO2 all year round.

Prem turned to AirGradient, a specialist in measuring indoor air quality in schools, who put AQI sensors into all main classrooms and common areas to continuously track the air quality 24/7 and estimate student exposure to PM2.5 and CO2.

After analysing thousands of data points, Prem drew two main conclusions. 

Firstly, at the height of the smoky season, even with powerful air purifiers running at maximum speed, it was not possible to bring PM2.5 levels down below the value of 10ug/m3 recommended by the World Health Organisation.

Secondly, CO2 levels in many classrooms exceeded recommended levels and so there were concerns that this may impact learning and possibly even important test scores.

Installing more air purifiers would not improve the CO2 situation but opening windows only made PM2.5 worse. So Prem looked towards a completely new technology and while visiting other international schools came across the CleanFlow positive pressure system (PPS).

Positive pressure systems take outside air, run it through a set of high-performance filters, and feed it into the classrooms. The higher pressure of clean air inside the classrooms prevents dirty air entering from outside. The results: near zero AQI inside the classrooms, even on very polluted days and low CO2 levels because fresh air is constantly fed into the classrooms.

The difference between purifier and positive pressure systems

In September 2020, Prem equipped all its main classrooms, sports facilities and common areas with CleanFlow positive pressure systems in order to ensure extremely low AQI inside the classrooms and high fresh air ventilation, so as to reduce COVID-19 transmission risks. It now achieves CO2 levels well within the recommendations for classrooms. 

Prem also undertakes regular air quality certifications from AirGradient. The last certification in February showed that Prem ensures air quality within the strictest WHO standards even during the smoky season. In February 2020, it achieved indoor air quality of only 6.33 μg/m³ PM2.5 (26 US AQI) when outside PM2.5 was 51.7 μg/m³ (141 US AQI).

Prem is very transparent about its air quality, publishing data on its air quality webpage and informing parents about current air quality within the school. The parents are extremely grateful for the steps that Prem takes and the school is happy to show all visitors how children learn in a clean air school.


Prem AQ Webpage:

Independent Certification of Prem’s Air Quality

Last Air Quality Report:

CO2 Classroom Recommendations COVID-19 Germany <1000 ppm

CO2 Classroom Recommendations COVID-19 US <800 ppm

Cognitive Performance at 1400 ppm

AirGradient. Air quality monitoring for schools.

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