Live Rensair air purification trial at QPCS school, London, UK

February 21, 2022 – 5 Min

Download the full QPCS school trial white paper

Executive summary

The trial currently being undertaken at QPCS school in London is demonstrating that a Rensair air purifier is successfully removing airborne Particulate Matter from poorly ventilated classrooms, down to a negligible level that is well below the safety thresholds recommended by leading health authorities.

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In theory, the cubic meterage and high occupancy of the trial classrooms demand three air purifiers per classroom to achieve the WHO’s recommended ventilation/purification rate of 10 litres per second per person. In practice, one single Rensair air purifier per classroom is managing to keep particulate levels down to almost zero.

Not only does this show that infection mitigation is achievable at a relatively low cost, an important aspect for schools with stretched budgets, but there is a significant energy saving as windows are no longer required to be fully opened throughout the school day. This results in a more comfortable teaching environment for staff and pupils.


Rensair, expert in portable hospital-grade air purification for the education sector, is staging a real-world trial at Queen’s Park Community School (QPCS) in Brent, London. 

The objective of the trial is to demonstrate the effectiveness of Rensair technology in removing Particulate Matter, including airborne viruses and bacteria, from high occupancy and poorly ventilated classrooms, without causing noise disturbance.

The direct benefit of the Rensair unit is to reduce the risk of airborne disease transmission, but also to improve room comfort and to reduce energy consumption, as classroom windows and doors do not have to remain permanently open.

What is Particulate Matter (PM)?

PM is a mixture of solid particles and liquid droplets found in the air that are in most part invisible to the naked eye. The size of PM is measured in microns (μg) – 1,000 microns make up 1 millimetre (mm). PM1 refers to Particulate Matter that is 1 micron in diameter, PM2.5 is 2.5 microns in diameter and PM10 is 10 microns in diameter. 

Disease can be transmitted by the inhalation of airborne bacteria and viruses, with the most serious illnesses occurring when microscopic PM aerosols penetrate deep into the lungs. The table below shows the size of various PM matter in microns:

Independent tests show that Rensair units are effective at cleaning particles as small as 16 nanometres (equivalent to 0.016 of a micron – 0.016 μg). The trial seeks to establish the effectiveness of a Rensair unit at maintaining a low level of Particulate Matter in a poorly ventilated classroom with high occupancy.


One Rensair air purifier is placed in each of two classrooms, operating only between 9am and 5pm during the Monday-Friday working week (i.e. not at night, weekends or half term).

In one classroom the Rensair unit is positioned at the back of the room, and in the other classroom at the front, closer to the teacher. Each room is equipped with 2 high quality sensors, located far away from each other and from the Rensair unit, and provide real time data on Particulate Matter, Temperature, CO2, Noise, Humidity and Light.

The different room positioning of the units together with the placement of two sensors in different areas of each classroom and away from the units should demonstrate if the units are efficient in cleaning air, and also if they manage to clean all the air in the room. 

Floor plan and equipment in classrooms A and B


The charts below show the data from the sensors for the various categories important for the classroom environment. The grey bars indicate the school hours when the Rensair units are in use. 
The units are switched off at night, during weekends and also during the recent 14th – 18th of February half-term.

a) PM1: The chart shows that the average PM1 readings are at almost negligible levels

There are no Indoor Air Quality standards specifically for fine PM1 particles. The chart shows that the sensor readings of PM1 have been negligible during school hours, averaging 3μg/m3 throughout the trial.

The PM1 readings registered a rise on the 2nd and 3rd March and the school was alerted. There was no unusual work being carried out at the school and air monitors registered that outdoor PM readings on those days were well within the previous month’s readings. Note that PM1 readings were significantly lower when the units were operating compared to the readings outside of school hours.

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b) PM2.5: The chart shows that the average PM2.5 readings are at almost negligible levels.

The EU Air Quality standard is for PM2.5 to remain below 20microns per cubic metre (μg/m3), whilst the guideline limit in the UK is 25μg/m3. The WHO recommends a more stringent limit of 15μg/m3, whilst the Taskforce for Lung Health has a lower target of 10μg/m3. 

The average PM2.5 readings throughout the trial have been 3μg/m3 during working hours. Similar to PM1, there was a 2 day rise in PM2.5 reading, although it remained low during working hours when the Rensair units were operating. 

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c) CO2:  The CO2 chart below shows rising CO2 levels when there is a high occupancy of the classrooms. This should be countered by opening windows for short durations between classes.

The UK HSE recommends CO2 levels to remain below 800 parts per million (ppm). As can be expected in poorly ventilated classrooms, CO2 levels will increase when there is very high occupancy. CO2 in itself will not cause harm and is a vital part of the environment, but research shows that high concentrations can reduce cognitive functions. 

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d) Noise: The registered classroom noise is higher than the operating sound generated by the Rensair unit. 

From an engineering perspective, it is hard to design an effective air purifier that does not generate noise, and excess sound would be a distraction in a learning environment. The Rensair unit operates in the classrooms on the medium fan setting, purifying 430m3 of air per hour at 52dBA. The dBA charts demonstrate that the ambient noise in the classroom is well in excess of the noise generated by the Rensair unit, confirming teacher feedback that the units are not a distraction. 

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e) Temperature: The temperature readings show a comfortable average of 21oC, with high and low readings of 18 and 23 during the trial period. 

This is decidedly warmer compared to when classrooms had windows and doors open (i.e. before the Rensair units were installed).


It is clear from the data that Rensair technology effectively removes Particulate Matter, including airborne viruses and bacteria, from high occupancy and poorly ventilated classrooms, without causing noise disturbance. Just one Rensair unit delivers 3.3 litres of clean air per second per person and renders a classroom safe in terms of viral and bacterial Particulate Matter. 

As can be seen from the 2 day instance of high Particulate Matter, the use of Rensair units substantially reduced the PM1 and PM2.5 levels within classrooms to within safe limits during school hours.

It is recommended that the classrooms are aerated between lessons to reduce the CO2 levels.

The charts will be updated twice weekly to show real-time data.

Read more about the trial, including comments from the school here.

Download the full QPCS school trial white paper

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