What is the best way to improve the air quality in a building? In the absence of clear guidelines, several researchers have developed tools for homeowners looking to reduce the risk of transmission.
For months, school air quality has been at the center of a huge public debate. However, while governments in several countries around the world are beginning to recognize the role of ventilation in the spread of COVID-19, the implementation of methods to improve indoor air quality is still being delayed.
However, from the start of the pandemic, poorly ventilated indoor areas were considered to be at high risk of transmission. The problem can arise anywhere: in restaurants, shopping malls, office towers … All public places are potential transmission sites. “Not only have very few adjustments been made since the start of the pandemic, but many buildings simply did not have the necessary equipment to manage air quality,” explains engineer Stéphane Bilodeau, who believes efforts to limit air transmission have led to this result. … far was “clearly inadequate.”
If poorly ventilated interiors put us at risk of contracting COVID-19, it is due to the accumulation of aerosols, tiny droplets that are constantly released when talking or breathing, and which can be contaminated with viral particles.
Although there are several measures to reduce the density of these aerosols, such as filtration, mechanical ventilation or even simple opening of windows, they do not have the same effect under all circumstances. Engineer Liangzhu (Leon) Wang of Concordia University in Montreal demonstrated this in a study published in a preliminary publication in January 2021. In a crowded restaurant, doubling the outside air flow can reduce air consumption. The risk of contracting COVID-19 is 35%. However, performed in the warehouse, the same procedure reduced the risk by only 0.1%. “The risk of airborne transmission inside a building is not universal; it varies depending on its size, the activities that we practice there, the distance between people or the time we spend there, says the researcher.
“The needs are very unequal,” says Stefan Bilodeau. There are simple methods for solving ventilation problems, but you need instructions, well-written manuals that can help you better equip buildings while avoiding misfire. “
This is what some researchers have tried to do by creating online tools for homeowners or managers that indicate the measures that could have the greatest impact on the air quality in their building.
The first of its kind was launched in June 2020 by a team of US researcher Jose Luis Jimenez, an aerosol expert at the University of Colorado. This has inspired other researchers who have developed similar guidelines, but applicable in different contexts around the world. This is the case of Leon Wang, whose web-based tool called CityRPI provides an inventory of various types of buildings found in several major Canadian cities.
For example, for a 10-story office tower located in Montreal, priority is first given to replacing filters in the aeration system with models capable of capturing up to 50% of particles less than one micrometer (MERV-13), and then the number is halved. people working on site and then install HEPA air filters in less ventilated areas.
“We especially want to spread information,” explains Mr. Wang. Before the pandemic, most people were unaware of what was happening to ventilation in their workplaces or in their children’s school. “
To develop their tool, Concordia researchers used government guidelines for various types of construction, such as schools, high-rise buildings, or grocery stores. “Much of the information needed to calculate the risk of transmission is proprietary. Therefore, to obtain our results, we relied on publicly available data on 29 building archetypes. However, our tool prompts the user to enter real information about their building to get personalized results. ”
Once compiled, this data shows whether a building would benefit from an air purifier, air exchanger system, or better to modify an existing ventilation system.
“The tool also shows how distancing gestures can affect the likelihood of transmission in different scenarios,” explains Leon Wang. In terms of school, for example, what happens to the risk if the number of students per class decreases to 10 instead of 30, or if the class is moved to a 100 square meter room instead of 50? “
However, for Professor Wang, this type of instrument is only a temporary measure. “If we want to avoid the next pandemics, we must completely rethink how we manage ventilation. A dynamic system equipped with CO sensors would be ideal.2 which can not only inform visitors about the ventilation status as soon as they enter, but can also control the ventilation so that this CO2 remains below a certain threshold. Some researchers recommend 600 ppm, others 800. The goal we need to achieve is 1000 ppm. This latter number is also the maximum allowed for schools by the Quebec Ministry of Education.
“With the pandemic, the public has realized that air quality plays an important role in the spread of disease,” adds Stefan Bilodeau. This was an indication of the flaws in the design of our buildings. This is good, and not just for infections, because research shows that in schools, air quality also affects the ability to concentrate. If we can take advantage of these benefits, it will be at least a positive outcome for COVID-19. “