Evaluation of Optimal Mechanical Ventilation Strategies for Schools for Reducing Risks of Airborne Viral Infection
2. Materials and Methods
2.1. Analysis Methods
2.2. The Wells–Riley Model
- Compare the performance of MV and demand control ventilation (DCV) systems using hourly simulations for a summer day (22 July) using the following as metrics: POI, CO2 concentration, and cooling energy use.
- Adjust the DCV set point (CO2 set point in ppm) and assess its effect on the probability of infection and cooling energy use.
- Perform a series of sensitivity analyses to determine the impacts of social distancing on the performance of MV and DCV including POI, indoor CO2 concentration, and cooling energy use.
- Establish any correlation between social distancing, number of infectors, and the resulting POI for MV.
- Assess variations in POI and cooling energy use for a range of ventilation rates and social distances for MV.
3. Results and Discussion
3.1. Performance Comparison for MV and DCV
- Will DCV be able to prevent high POI while still maintaining low cooling energy consumption compared to the conventional MV if the CO2 set points are adjusted?
- Will MV be able to outperform DCV considering cooling energy use and indoor air quality (i.e., CO2 concentration and infection risk) when optimized?
3.2. DCV Set Point Analysis
3.3. Sensitivity Analysis of MV
3.4. Impact of the Number of Infectors
3.5. Correlation of POI and Cooling Energy
- When considering the risk of infection transmission, optimized MV could be more energy-efficient than the DCV system according to the findings of this study.
- Without adjusting its CO2 setting, the DCV system supplies low ventilation rates, resulting in significant POI increases within the school. However, adjusting the DCV set point from 1000 ppm to 600 ppm results in a significant POI reduction from 0.93 to 0.057, with a 50% increase in the total cooling energy needs.
- MV can reduce the POI to 0.051 when operating with a higher ventilation rate of 2 ACH, double the required rate by the ASHRAE standard 60.2 for schools. The DCV can lower the POI to 0.057 when operating with a 600 ppm set point and delivering a ventilation rate of 4 ACH. In this case, MV consumes 617 kWh/day while DCV needs 743 kWh/day.
- An optimal ventilation rate of 2 ACH and social distance of 2 m are recommended to deliver acceptable levels of POI, cooling energy use, and indoor CO2 concentration. These optimal settings would limit the POI to 0.036 while achieving the lowest cooling energy use of 583 kWh/day for the school.
- Increasing the ventilation rate is more effective in reducing the POI than increasing the social distancing. However, the reduction in POI occurs with an increase in cooling energy use when the ventilation rate is increased. For instance, increasing the social distance from 1 m to 2 m would lower the POI by 28%, while reducing the cooling energy need by 7%. On the other hand, increasing the ventilation rate from 1 ACH to 2 ACH would lower the POI by 49%, while increasing the cooling energy demand by 25%.
- The POI remains between 0.036 and 0.13 when operating with a 2 ACH ventilation rate and 2 m social distancing even if the number of infectors is increased from 1 to 5.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|Number of Floors||2|
|Gross Floor Area||3123 m2|
|Wall Construction||2 cm plaster outside + 20 cm concrete hollow block + 5 cm expanded polystyrene + 2 cm plaster inside|
|Roof Construction||1 cm built-up roofing + 20 cm concrete roof slab + 5 cm expanded polystyrene + 1.5 cm plaster inside|
|Glazing Type||Double Clear with PVC framing|
|Air Infiltration||0.7 ACH|
|Number of Students per Area in classrooms||0.5/m2|
|Lighting Power Density||5 W/m2|
|Equipment Power Density||4.7 W/m2|
|HVAC System||DX Packaged Air Handling Unit|
|Cooling Set Point||23 °C|
|Ventilation System||Mechanical ventilation with fixed outdoor air fraction (15%)|
|Energy Efficiency Ratio (EER)||8.5|
|Case||Case Date||Place Type||Total Occupants||Primary Infected Cases||Secondary Infected Cases||V (m3)||n|
|p (m3/h)||q (quanta/h)|
|1||24 January 2020||Restaurant||21||1||9||127||0.6||1.25||1.1||42.1|
|2||20 February 2020||Meeting room||14||1||≥11||189||0.2||9.5||1.1||42.1|
|3||10 March 2020||Choir hall||61||1||33–53||810||0.35–1.05||2.5||1.1||195.5|
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Almaimani, A.; Alaidroos, A.; Krarti, M.; Qurnfulah, E.; Tiwari, A. Evaluation of Optimal Mechanical Ventilation Strategies for Schools for Reducing Risks of Airborne Viral Infection. Buildings 2023, 13, 871. https://doi.org/10.3390/buildings13040871
Almaimani A, Alaidroos A, Krarti M, Qurnfulah E, Tiwari A. Evaluation of Optimal Mechanical Ventilation Strategies for Schools for Reducing Risks of Airborne Viral Infection. Buildings. 2023; 13(4):871. https://doi.org/10.3390/buildings13040871Chicago/Turabian Style
Almaimani, Ayad, Alaa Alaidroos, Moncef Krarti, Emad Qurnfulah, and Alok Tiwari. 2023. "Evaluation of Optimal Mechanical Ventilation Strategies for Schools for Reducing Risks of Airborne Viral Infection" Buildings 13, no. 4: 871. https://doi.org/10.3390/buildings13040871