Controlled mechanical ventilation can not only dilute or even neutralize pathogens indoors but also reduce exposure to the particulate carcinogen
There
ventilation always our ally to reduce the concentration of indoor pollutants and, therefore, to mitigate discomfort and health risks, including the risk of infection with pathogens airborne. In the past, when buildings were less airtight, ventilation was obtained by infiltration through the building envelope or through opening windows: today it can be the result of specially designed systems, mainly of a mechanical type. In fact, by ventilation we mean theentry of outside air (and equal indoor air output) in an indoor environment with natural means (natural ventilation) o mechanical (controlled mechanical ventilation, CMV).
For decades despite the attention of architects and engineers of indoor environments towards the thermal comfort, odor control, air quality and energy saving, ventilation remained in a corner in the design and operation phases of a building. Yet we spend over the 90% of our time indoorsthe predominant dose of pollutants is inhaled in these environments and as we – alas late – also learned during the last pandemic, we get infected in indoor environments.
So how important is ventilation and how much can it help us in our lives? And at the same time, is ventilation a cost or is it a strategic investment?
I will limit my analysis to
school
i.e. to our school classes. According to MIUR data, we had a total of 8.3 million male and female students for the 2020/2021 school year divided into approximately 369,000 school classes, with an average crowding of 22-23 students per class.
Ventilation and energy saving
Take two identical school classes, one with controlled mechanical ventilation, the other with simple natural ventilation (which can be improved by opening windows – ventilation). With the same ventilation, i.e. with the same average CO2 concentration (for example 1000 ppm), and with the same thermo-hygrometric conditions (with the same “comfort”), controlled mechanical ventilation results in energy savings for the middle class on the national territory of around 400 €/year, with higher values in the north and lower values in the south. An annual saving on the entire national territory of no less than 150 million euros.
Ventilation and reduction of exposure to pollutants
With each inhalation we let air and numerous pollutants enter our lungs. Among these the airborne dust (atmospheric particulate) have been defined by WHO as group 1 carcinogenthat is to say certain risk of lung cancer in case of exposure. Furthermore, we know that there is no safe threshold and therefore it is necessary to reduce exposure to this worldwide pollutant as much as possible to reduce the risk. Again considering two identical school classes, differing only in the type of ventilation, it has been demonstrated that exposure to ultrafine particles (the most impacting on health) is reduced from 50% to 99% (depending on the filter adopted from G4 to HEPA) in classes with controlled mechanical ventilation compared to natural ventilation. This reduction is approximately 50% with reference to the largest “fine particles”, PM10. It therefore means that life in ventilated environments (with filtration of the incoming air especially in urban areas) characterized by a drastic reduction in the received dose of airborne dust and the consequent impacts on health (in the alveolar region alone, a citizen receives around 20 billion particles per day, with over 90% from indoor environments)⁴.
Ventilation and socio-economic benefits
How much does the level of ventilation affect our performance? Let’s take this time the typical Danish classroom and the Swedish one, both with controlled mechanical ventilation but with different ventilation rates (6 L/s per student for the Danish classroom and 8.4 L/s per student for the Swedish one). The Swedish requirement was found to improve school performance by an average of 6%.⁵ Consequently, improving classroom air quality in Danish schools to the level already compulsory in Sweden would produce an average annual increase in GDP of €173 million and a average annual increase in the public budget of 37 million euros over the next 20 years (for a population equal to one tenth of Italy’s): and the effect will generally increase as more pupils complete their education in favorable study conditions. Generally speaking, increasing the ventilation rate in classrooms in the range from 2 L/s-person (classroom with natural ventilation) to 10 L/s-person (classroom with controlled mechanical ventilation) can bring not only significant benefits in terms of learning performance and student attendance but also relevant economic benefits for the whole country.
Ventilation and airborne transmission of respiratory pathogens
Instead of dealing with the diseases inside the human body, theengineering can establish further lines of defense by intercepting and neutralizing pathogens before they reach humans or by diluting them so much that they cannot accumulate an infectious load⁶. Good engineering can create sound public health, for example with good ventilation. As of 4 January 2023, a total of more than 4.8 million cases of COVID19, 25104 hospitalisations, 567 intensive care unit admissions and 85 deaths have been reported in the school-age population (< 19 years)⁷. With reference to the entire clinical pathway, the costs for each hospitalization, including rehabilitation costs, ranged from €6,000 to over €32,000, depending on the patient's clinical conditions⁸. it has been demonstrated that good controlled mechanical ventilation (greater than the 5 volumes now required by current legislation or equivalent to 10 L/s-student) reduces the transmission of infection by about 80%⁹. Significantly reducing infections among students (among the almost 5 million infected) also means containing the infection in the family environment and reducing the days of emergency where the use of personal protective equipment is required. With an average cost of around €1 for an FFP2 facial filter (cost ranging from an initial value >€10 to less than €1 currently), each day of emergency avoided would mean only with reference to the student population a savings of over 8 million eurosof course regardless of the pathogen.
Given the benefits, how much would the adoption of controlled mechanical ventilation in schools cost us? It starts from a cost per classroom of about 4000 €, which would involve an investment of 1.5 billion euros, without considering the possible reduction in the unit cost as the number of systems installed increases. There are still those who can consider controlled mechanical ventilation an unacceptable cost?
F. Busato, A. Cavallini, A theoretical study of air change in Italian schools: energetic aspects, air quality and Sars-CoV-2 infection risk assessment Part 2, AiCARR Journal, 2021, vol. 70 n.5, pp. 49-55.
F. Busato, A. Cavallini, A theoretical study of air change in Italian schools: energetic aspects, air quality and Sars-CoV-2 infection risk assessment Part 1, AiCARR Journal, 2021, vol. 68 n.3, pp. 52-55.
Stabile et al., 2019. The effect of the ventilation retrofit in a school on CO2, airborne particles, and energy consumptions. Building and Environment 156, 1–11.
⁴Buonanno et al., 2012. A comparison of submicrometer particle dose between Australian and Italian people. Environmental Pollution 169, 183-189
⁵Wargocki et al., 2020. The relationships between classroom air quality and children’s performance in school. Building and Environment 173, 106749 ⁶Forsberg, CW “Public Health is a Job for Engineers.” ASME. mechanical engineering. March 2022; 144(2): 36–41. https://doi.org/10.1115/1.2022-MAR2 ⁷ EXTENDED REPORT ISS – COVID-19: SURVEILLANCE, IMPACT OF INFECTIONS AND VACCINATION EFFECTIVENESS, National Update 06/01/2023. ⁸Foglia et al., COVID‑19 and hospital management costs: the Italian experience, BMC Health Services Research (2022) 22:991, https://doi.org/10.1186/s12913-022-08365-9
⁹Buonanno G, Ricolfi L, Morawska L and Stabile L (2022) Increasing ventilation reduces SARS-CoV-2 airborne transmission in schools: A retrospective cohort study in Italy’s Marche region. Front. Public Health 10:1087087. doi: 10.3389/fpubh.2022.1087087)
George Buonanno* Professor of Environmental Technical Physics at the University of Cassino and at the Queensland University of Technology in Brisbane in Australia
February 11, 2023 (change February 11, 2023 | 10:26)
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