Effect Of Air-To-Air Energy Exchangers Of Ventilation Systems On Indoor Containment Of Airborne Transmission
Department of Mechanical Engineering, University of Saskatchewan, Canada
Ventilation is one of the effective engineering measures to control airborne transmission indoors, and hence, 18 ventilation guidelines were established from different countries during the covid pandemic. In the ventilation technique, the outdoor airflow rate is increased to reduce the concentration of infectious aerosols indoors. However, to maintain a comfortable indoor environment, it is essential to condition the ventilation air before it enters the building space leading to increased energy consumption. Air to air energy exchanger (AAEE) is an energy recovery equipment used in the ventilation systems to reduce the energy required for conditioning the ventilation air. In AAEE, the energy from the exhaust air is used to precondition the ventilation air. Introducing AAEE in the ventilation system (i) reduces the heating/cooling equipment load, and thereby the ventilation rate can be increased, which in turn decreases the indoor aerosol concentration, and (ii) increases the concentration due to the possibility of contaminant transfer while recovering energy. As a result, AAEE may increase or decrease the concentration depending on its effectiveness and contaminant transfer ratio. However, most pandemic ventilation guidelines didn’t encourage the application of AAEE in the pandemic ventilation system due to contaminant transfer possibilities. On the other hand, there is also no direct literature evidence for the comprehensive effect of AAEE on the indoor concentration of aerosol. Hence, to address this research gap, this study analyzes the effect of AAEEs on the indoor airborne transmission of infectious aerosols. The study will be useful for developing an energy-efficient pandemic ventilation system.
Literature Review On The Capture Of Aerosols Generated By Dental Care
WHO indicates that “COVID-19 spreads between people through […] contact with infected people via mouth and nose secretions. That includes saliva, respiratory secretions or secretion droplets.” Among health practices, dentistry poses a particularly high risk due to the close proximity of dentists and health staff to the patient’s mouth, making them exposed to this disease and, more generally, every disease being transmitted the same way. This risk is amplified as dentistry often involves operations that generate saliva and/or blood aerosols, which are excellent vectors for infectious agents. These vectors may directly reach the health staff, be suspended in the room or deposit on surfaces. This could lead to contamination of both the personnel and following patients by direct contact with aerosols or indirect contact with contaminated surfaces. Ventilation systems could help lower the risk of propagation but not all dental care centers are equipped with mechanical ventilation and tools that capture aerosols at the emitting location are not widespread. The French National Order of Dentists gave specific recommendations during the COVID-19 pandemic, most of them targeting personal protective equipment and air renewal. These recommendations were necessary due to the urgency of the situation but are inappropriate for long-term use. Hence, it is required to determine ways to improve the capture or dilution of aerosols generated by dental procedures. An upcoming study will cover these topics. Beforehand, this literature review describes current knowledge regarding generation of aerosols by dental care and efficiency of tools that are currently used to capture aerosols.
Designing an Efficient Ventilation System to Avoid Covid-19 Transmission in Site Sheds and Portable Lunchrooms
Site sheds and portable lunchrooms are largely used by workers on building and construction sites although they are not permanently ventilated. Ventilation only occurs naturally by opening windows and doors. However, when the weather is cold or rainy, workers keep the openings closed in order to maintain an acceptable thermal comfort. This situation leads to significant transmission risks for diseases like Covid-19 through aerosols, given low air change rates and high occupancy rates (about one person for two square meters) in such environments, combined with the impossibility of wearing masks during lunch. Because social distancing recommended in case of pandemics cannot be applied, some Plexiglas screens are used as separations to control direct droplets transmission. Now the challenge is to design a mechanical ventilation system with many constraints; it must indeed 1) not be based on mixing (to avoid aerosol transmission), 2) rapidly dilute aerosols in each location, 3) be compatible with portable equipment (low electrical power consumption and low weight), 4) be compatible with occupant thermal comfort (low air velocities and pre-heated supply air), 5) not degrade the use of current equipment (lighting, sink, refrigerator, etc.). We propose a design that works within these constraints. The proposed ventilation system was evaluated based on an analysis of airflow patterns by CFD and validated with on-site measurements of carbon dioxide concentration. Beyond the pandemic period, site shed ventilation presents the opportunity to greatly increase the IAQ of these work premises.
Acknowledgements: This work was conducted by a working group created by the French national health insurance fund (CNAM) comprising regional health insurance centers (Carsat), industrial partners and the French national institute for occupational safety and health (INRS).