Air purification in classrooms | Opening the window, the only solution?

Delivery of CO detectors₂ in schools is driving many teachers to want air purification methods other than opening windows. Here are three available technologies.

Mathieu Perreault
The Press

Focus on ultraviolet

A Montreal company, Sanuvox, has sold ultraviolet (UV) air purifiers to hundreds of schools in British Columbia – and thousands in Ontario – according to its founder, Normand Brais. Last year, Quebec parents who wanted to fund the purchase of Sanuvox UV purifiers for their children’s schools themselves were met with refusal from the school authorities.

“We would like the Quebec government to admit that we will not put purifiers because it is too expensive, instead of saying that CO detectors₂ will be a solution to the problem,” says the engineer, a former professor at Polytechnique Montréal.

For a middle class, with an area of ​​100 m^⁠2, two Sanuvox units with a capacity of 300 cu.³ per minute, according to Mr. Brais. On the Internet, sites report prices ranging from $1,500 to $2,000 for these models, an order of magnitude confirmed by Mr. Brais. This means that it would cost more than $3,000 per class, not including the installation and replacement of UV bulbs, which last a few years. In comparison, the budget of CO detectors₂ was 75 million for 90,000 units including installation, or just over $800 per class.

Purification by these two Sanuvox devices would correspond to three classroom air changes per hour. In a document published last winter, the University of Toronto recommended six air changes per hour instead.

In addition to the discomfort, opening the windows is very expensive in terms of heating in winter, according to Mr. Brais. “Since the two oil shocks of the 1970s, there has been a lot of emphasis on energy efficiency,” says Mr. Brais. This has led to buildings that are much less ventilated than before. »

Boil the droplets

Another Montreal company, Hypertec, claims to have designed a prototype purifier using another technology, the Hyperion. It might only cost $500 per class. “There are no installation costs – you plug the device into a normal power outlet – nor maintenance costs, no bulbs to replace”, says André Lamarre, vice-president of Hypertec .

Hypertec specializes in technology, cloud computing and cybersecurity, including working extensively with Ontario’s telemedicine program, the most advanced in Canada before the pandemic. Its Hyperion is being validated in an American laboratory. Hypertec is also working toward certifications with Canadian and US technical and government agencies.

How does it work ? The electric field in the Hyperion “boils the droplets on which viruses and bacteria travel through the air,” says Lamarre. UV rays, on the other hand, alter viral proteins. According to Mr. Lamarre, the Hyperion technology is similar to another technology, ionization, but unlike the latter, it does not create ozone. Ionization works by creating charged particles on which the virus particles cling, but it cannot be used on a large scale because of this creation of ozone.

Nearly “35 air changes per hour”

A third technology, low-wavelength UV, is currently being used in some buildings in the United States and being tested in a few retirement homes in Nova Scotia. One of the researchers most involved in the field, radiophysicist David Brenner of Columbia University, New York, says the cost is US$1,000 to clean the air of a middle class, not counting the changes subsequent blisters. “Below 235 nanometers (nm) in wavelength, UV does not cause damage to cells in the skin and eyes, so you don’t need to put bulbs in boxes where you pass the air, said Mr. Brenner. We can use our 222 nm bulbs to directly purify the ambient air, which makes it possible to achieve the equivalent of 35 air changes per hour. »

Kenneth Rockwood, a geriatrician at Dalhousie University and responsible for testing Mr. Brenner’s light bulbs in nursing homes, chose this technology in conjunction with his son, Michael Rockwood, who is an electronic engineer. “It should cost a lot less than purification devices using traditional UV at 254 nm,” says Dr.^r Rockwood. The clinical trial will cost a total of 1.8 million and will be completed in spring 2023.

The American Conference of Governmental Industrial Hygienists, which brings together officials responsible for formulating health standards, has just increased by a factor of seven the limit for UV exposure at 222 nm. This corresponds, according to Mr. Brenner, to eight hours under the lamps he designed.

Mr. Brais of Sanuvox believes that low wavelength UV has the potential to create ozone. Mr. Brenner replies that it is not, but the D^r Rockwood is still considering placing ozone detectors in rooms where UV-222 nm bulbs are installed, as ozone is irritating to the lungs.