Toward Immune Buildings: Lessons Learned from the COVID-19 Pandemic and Its Aftermath

The COVID-19 (SARS-CoV-2) pandemic has not yet ended. The COVID-19 pandemic has been the worst human health crisis after the Second World War [1]. Over 90% of SARS-CoV-2 cross-infections occur in confined spaces (e.g., buildings and transportation cabins), which reveals that confined environments and their associated air systems are vulnerable to infectious disease transmission. Evidence of SARS-CoV-2 indoor transmission has been documented, such as in residential buildings [2], hospitals [3], restaurants [4], offices [5], airport terminals [6], aircraft cabins [7], high-speed trains [8], buses [9], and ships [10], etc. Vaccination has played a crucial role in dampening the SARS-CoV-2 risk; however, it still may not be able to terminate the pandemic in the near future due to the possibility of continuous virus variation. In addition to improving the vaccination rate and vaccine effectiveness, strategies that can reduce the human exposure to various infectious pathogens are pressingly needed, both during and after the pandemic. The experience obtained and lessons learned from one event will always provide great insights into the handling of similar ones in the future. &nbsp;</p

Integrated inverse design of ventilation for an aircraft cabin

Cabin ventilation is crucial for maintaining thermal comfort and air quality for passengers and crew. The genetic algorithm, proper orthogonal decomposition (POD), and adjoint method have been proposed to inversely design the cabin ventilation. However, each method has its cons and pros. This paper proposed to integrate the above three methods in cascades. The genetic algorithm was applied first in the first stage to roughly circumscribe the ranges of design parameters. Then POD was applied in the next stage to further narrow the ranges and estimate the optimal parametric sets for each design criterion. The estimated optimal design from POD was supplied to the adjoint method for fine tuning. The air-supply parameters of a five-row aircraft cabin were inversely designed to achieve the minimum absolute value of the predicted mean vote (PMV) and the minimum averaged mean age of air. The results showed that the integrated method was able to improve the design stage by stage. The integrated method has superior advantages to assure the optimal design while minimizing the computing expense

Impact of Seat Inclination and Misalignment on Airborne Pollutant Transport in a Single-Aisle Aircraft Cabin

Airborne pollutant transport in an aircraft cabin is greatly affected by the created airflow. The seat layout can impact the flow and thus the pollutant transport. Most studies have adopted symmetric upright seats for simplicity. The influence of seat inclination and seat misalignment on airflow and pollutant transport is still unclear. This investigation adopted a validated computational fluid dynamics (CFD) method to study the airflow and airborne pollutant distribution in a single-aisle cabin with seven rows of seats. The pollutant was assumed to be released from a passenger seated in the middle of three adjacent seats. A total of five different seat layouts were considered, including all of the upright seats, the inclination of three adjacent seats, the inclination of all of the seats in half a cabin, the inclination of all of the seats in a whole cabin, and the misalignment seat rows across the aisle. The flows in both the cross and longitudinal sections were compared. The pollutant concentrations in the respiratory zone of the passengers in different seats were adopted to evaluate the cross-contamination. The results revealed that the symmetric seat layout aids to circumscribe the released pollutant in a small region and reduces the cross-contamination either by maintaining the upright seats or inclining all of the seats. Contrarily, any inclination of seats or a misalignment of seat rows should be avoided during the pandemic since an asymmetric seat layout would generate asymmetric flow and strengthen the spreading of pollutants

Toward Immune Buildings: Lessons Learned from the COVID-19 Pandemic and Its Aftermath

The COVID-19 (SARS-CoV-2) pandemic has not yet ended [...

A Modified Surgical Face Mask to Improve Protection and Wearing Comfort

Wearing face masks is essential for reducing infection during the COVID-19 pandemic. However, ordinary surgical face masks can provide only moderate protection. The N95 face masks should provide sufficient protection but may impose complaints about breathing difficulty or even impair respiratory health. This investigation proposed a novel face mask modified from the surgical face mask to improve both protection and comfort. The filter material of the surgical face mask was covered and sealed on a cardboard support frame but with openings for air permeating through. The modified face masks were worn by a test subject for measuring the air contents inside the face masks. The protection performance was evaluated by the overall PM1 filtration efficiency. The concentrations of CO2, O2, N2, and water vapor were adopted to evaluate the breathing comfort. The performance of the proposed face mask was compared with the market-available surgical and N95 face masks. In addition, CFD modeling was adopted to investigate the dynamic air exchange of the face mask with respiration and the surrounding air. Impacts of the air sampling tube positions on the measurement results were also examined. The results revealed that the overall PM1 filtration efficiency of the modified face mask could reach 96.2%, which was much higher than that of the surgical face mask and only slightly lower than the N95 face mask. As compared with the N95 face mask, the modified mask reduced the respiratory flow resistance and the concentrations of CO2 and water vapor and thus increased the O2 content and breathing comfort

Modeling and Measuring the Leaked-Air Rate into the Insulation Layer of a Single-Aisle Aircraft Cabin

Leaked air from an aircraft cabin into its envelope walls through cracks can lead to a large amount of moisture condensation on inner shell skins and in insulation layers. The leaked-air rate is subject to the stack pressure difference and the geometry of the cracks. So far, the impacts of the crack sizes and positions, and the flight conditions on the resulting leaked-air rate have been unclear. This investigation adopts validated computational fluid dynamics (CFD) to model leaked flow, pressure, and temperature distribution in a single-aisle aircraft cabin. Impacts of the flight cruising altitude, crack size and position, and flow blocker on the leaked-air rate were examined. In addition, measurements were conducted in a reduced-scale cabin mockup in an environmental chamber to mimic flight conditions. Obtained test data were adopted to validate CFD modeling. Results reveal that a higher cruising altitude of a flight results in greater leaked-air rate from the cabin to the envelope walls due to the larger temperature difference. The smaller the crack size was, the lower the leaked-air rate. In addition, more cracks farther away from the neutral plane lead to a greater leaked-air rate. A flow blocker in the middle of the insulation layer reduced the leaked-air rate by 34.5%

An Aisle Displacement Ventilation System for Twin-Aisle Commercial Airliner Cabin

The environmental control system in most commercial airliner cabins supplies air from shoulder and ceiling level and exhausts air at floor level on both sides of the cabin walls. The ventilation system mixes air in the cabins to create a relative uniform air temperature distribution which is great for passengers’ thermal comfort. However, the mixing ventilation also enhances airborne contaminant transfer. Many displacement ventilation methods have been proposed to use in aircraft cabins, but the disadvantages of the ventilation approach are usually creating draft on the passengers’ ankles and high air temperature stratification between passengers’ heads and feet. This investigation developed an aisle displacement ventilation (ADV) system which can reduce air temperature stratification effectively without occupying the legroom space under the seats, so it is good for passengers and crew members’ comfort and friendly for luggage storage, in addition, it can also be easily installed in aircraft cabins. By installing the system in a five-row, twin-aisle cabin mockup, our study found that the ADV system can create a low air velocity distribution in the cabin and can maintain an acceptable air temperature stratification without draft. The system created an uprising airflow which can effectively remove airborne contaminant which was generated from index passengers’ respiratory activities. The experimental data were used to validate a computational-fluid-dynamics (CFD) program. The validated CFD program was used to compare the ADV with under-seat displacement ventilation (USDV) and underfloor air distribution (UFAD) system along the aisles. The comparison results show that the ADV had obvious better thermal comfort than the other two systems, and the cabin air quality of the three ventilation systems was similar, all far better than the “perfectly-mixed” ventilated condition

Impact of Seat Inclination and Misalignment on Airborne Pollutant Transport in a Single-Aisle Aircraft Cabin

Airborne pollutant transport in an aircraft cabin is greatly affected by the created airflow. The seat layout can impact the flow and thus the pollutant transport. Most studies have adopted symmetric upright seats for simplicity. The influence of seat inclination and seat misalignment on airflow and pollutant transport is still unclear. This investigation adopted a validated computational fluid dynamics (CFD) method to study the airflow and airborne pollutant distribution in a single-aisle cabin with seven rows of seats. The pollutant was assumed to be released from a passenger seated in the middle of three adjacent seats. A total of five different seat layouts were considered, including all of the upright seats, the inclination of three adjacent seats, the inclination of all of the seats in half a cabin, the inclination of all of the seats in a whole cabin, and the misalignment seat rows across the aisle. The flows in both the cross and longitudinal sections were compared. The pollutant concentrations in the respiratory zone of the passengers in different seats were adopted to evaluate the cross-contamination. The results revealed that the symmetric seat layout aids to circumscribe the released pollutant in a small region and reduces the cross-contamination either by maintaining the upright seats or inclining all of the seats. Contrarily, any inclination of seats or a misalignment of seat rows should be avoided during the pandemic since an asymmetric seat layout would generate asymmetric flow and strengthen the spreading of pollutants