ABSTRACT
Online learning has drawn much more attention since the outbreak of COVID-19. Most related studies have focused on online platform design and instructional design. However, the physical environment where online learning is conducted (e.g., students' homes) is rarely studied. To understand the thermal conditions in students' online learning environment and its impact on students' thermal comfort and their performance during online learning, an experiment, including both objective measurement and subjective assessment, was conducted in a student's apartment. Thirty university students participated in this experiment, and they were randomly assigned into six groups (three thermal conditions (i.e., control, cold, and hot) × two-course durations). Both environmental parameters (i.e., air temperature, radiant temperature, air velocity, etc.) and physiological parameters (i.e. skin temperatures) were measured at the same time. Besides, students' thermal sensation, acceptance, and learning performance were self-evaluated and collected through questionnaires. Results showed that participants' thermal sensation was positively correlated with their mean skin temperature (MST) and the operative temperature (To) in the apartment (MST: ρ = 0.94, p < 0.001; To: ρ = 0.91, p < 0.001), yet no significant relation with their personal characteristics was observed in the current study, which might be caused by the small sample size. Moreover, inverted U-shape relationships were identified between participants' perceived performance and their thermal sensation/MST/To. When students felt slightly cool (TSV = -0.3), they thought they could reach their best performance. This study revealed the impacts of the thermal environment on students' online learning performance, more performance tasks could be conducted in the future to examine the impacts in more detail.
ABSTRACT
Current IoT applications in indoor air focus mainly on general monitoring. This study proposed a novel IoT application to evaluate airflow patterns and ventilation performance using tracer gas. The tracer gas is a surrogate for small-size particles and bioaerosols and is used in dispersion and ventilation studies. Prevalent commercial tracer-gas-measuring instruments, although highly accurate, are relatively expensive, have a long sampling cycle, and are limited in the number of sampling points. To enhance the spatial and temporal understanding of tracer gas dispersion under the influence of ventilation, a novel application of an IoT-enabled, wireless R134a sensing network using commercially available small sensors was proposed. The system has a detection range of 5-100 ppm and a sampling cycle of 10 s. Using Wi-Fi communication, the measurement data are transmitted to and stored in a cloud database for remote, real-time analysis. The novel system provides a quick response, detailed spatial and temporal profiles of the tracer gas level, and a comparable air change rate analysis. With multiple units deployed as a wireless sensing network, the system can be applied as an affordable alternative to traditional tracer gas systems to identify the dispersion pathway of the tracer gas and the general airflow direction.
ABSTRACT
Time-variant positive air pressure in a drainage stack poses a risk of pathogenic virus transmission into a habitable space, however, the excessive risk and its significance have not yet been sufficiently addressed for drainage system designs. This study proposes a novel measure for the probable pathogenic virus transmission risk of a high-rise drainage stack with the occurrence of positive air pressure. The proposed approach is based on time-variant positive air pressures measured in a 38 m high drainage stack of a full-scale experimental tower under steady flow conditions of flow rate 1-4 Ls-1 discharging at a height between 15 m to 33 m above the stack base. The maximum pressure and probabilistic positive air pressures in the discharging stack ventilation section with no water (Zone A of the discharging drainage stack) were determined. It was demonstrated that the positive air pressures were lower in frequency as compared with those in other stack zones and could propagate along the upper 1/3 portion of the ventilation pipe (H' ≥ 0.63) towards the ventilation opening at the rooftop. As the probabilistic positive pressures at a stack height were found to be related to the water discharging height and flow rate, a risk model of positive air pressure is proposed. Taking the 119th, 124th, 140th and 11,547th COVID-19 cases of an epidemiological investigation in Hong Kong as a baseline of concern, excessive risk of system overuse was evaluated. The results showed that for a 20-80% increase in the frequency of discharge flow rate, the number of floors identified at risk increased from 1 to 9 and 1 to 6 in the 34- and 25-storey residential buildings, respectively. The outcome can apply to facilities planning for self-quarantine arrangements in high-rise buildings where pathogenic virus transmission associated with drainage system overuse is a concern.
Subject(s)
COVID-19 , Air Pressure , Hong Kong , Humans , Models, Theoretical , SARS-CoV-2ABSTRACT
Aerial dispersion of human exhaled microbial contaminants and subsequent contamination of surfaces is a potential route for infection transmission in hospitals. Most general hospital wards have ventilation systems that drive air and thus contaminants from the patient areas towards the corridors. This study investigates the transport mechanism and deposition patterns of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) within a typical six bedded general inpatient ward cubicle through numerical simulation. It demonstrates that both air change and exhaust airflow rates have significant effects on not only the airflow but also the particle distribution within a mechanically ventilated space. Moreover, the location of an infected patient within the ward cubicle is crucial in determining the extent of infection risk to other ward occupants. Hence, it is recommended to provide exhaust grilles in close proximity to a patient, preferably above each patient's bed. To achieve infection prevention and control, high exhaust airflow rate is also suggested. Regardless of the ventilation design, all patients and any surfaces within a ward cubicle should be regularly and thoroughly cleaned and disinfected to remove microbial contamination. The outcome of this study can serve as a source of reference for hospital management to better ventilation design strategies for mitigating the risk of infection.