Built Environment & Energy Laboratory
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Chen, C.*, Zhao, B., Lai, D., Liu, W. (2018). A simple method for differentiating direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms. Building Simulation, 11, 1039-1051. (Particle dispersion, Infectious particle, Building)

Many airborne infectious diseases can be transmitted via exhaled contaminants transported in the air. Direct exposure occurs when the exhaled jet from the infected person directly enters the breathing zone of the target person. Indirect exposure occurs when the contaminants disperse in the room and are inhaled by the target person. This paper presents a simple method for differentiating the direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms. Experimental data for 191 cases were collected from the literature. After analyzing the data, a simple method was developed to differentiate direct and indirect exposure in mixing and displacement ventilated rooms. The proposed method correctly differentiated direct and indirect exposure for 120 out of the 133 mixing ventilation cases and 47 out of the 58 displacement ventilation cases. Therefore, the proposed method is suitable for use at the early design stage to quickly assess whether there will be direct exposure to exhaled contaminants in a mechanically ventilated room. 

Bian, Y., Wang, R., Ting S.H., Chen, C.*, Zhang, L.* (2018). Electrospun SF/PVA nanofiber filters for highly-efficient PM2.5 capture. IEEE Transactions on Nanotechnology, 17, 934-939. (Particle filtration, Particulate matter, Building) 

Particulate matter (PM) air pollution is associated with various adverse health effects. Heavy outdoor air pollution, especially smog, has significantly impacted the living quality of residential environments. Here, we report the fabrication of silk fibroin/polyvinyl alcohol (SF/PVA) nanofiber air filters for the filtration of PM pollution using the electrospinning technique. Silk fibroin is a type of protein fibers, which is widely available with excellent environmental sustainability, and PVA is commonly used for continuous nanofiber fabrication. Our results showed that the PM2.5 removal efficiency of the SF/PVA filter was 99.11 ± 0.24%, which was about 10% higher than that of the pure PVA filter under the same pressure drop of 50 Pa. In a 24-h filtration test, the filtration efficiency of this composite SF/PVA filter remained at a high value of 98.97% after 24 h. The results indicate the superior filtration performance of the SF/PVA nanofiber air filter, which holds a great promise in PM pollution prevention. 

Liu, C.*, Yang, J., Ji, S., Lu, Y., Wu, P., Chen, C.* (2018). Influence of natural ventilation rate on indoor PM2.5 deposition. Building and Environment, 144, 357-364. (Particle deposition, Particulate matter, Building)

Particle deposition can significantly affect occupants' exposure to PM2.5 in indoor environments. However, there is a lack of experimental data for the PM2.5 deposition rate under different ventilation rates in naturally ventilated rooms. This work experimentally examined the influence of natural ventilation rate on PM2.5 deposition in two university classrooms in Nanjing, China. The results showed that the deposition rate was linearly associated with the natural ventilation rate for both classrooms. An empirical equation was developed to correlate the PM2.5 deposition velocity with the natural ventilation rate. The developed empirical equation was then applied in three scenarios to illustrate the influence of natural-ventilation-rate-dependent PM2.5 deposition velocity on the infiltration factor, I/O ratio, and air cleaner selections. The analysis showed that the PM2.5 infiltration factor and I/O ratio were less sensitive to the natural ventilation rate when the influence of natural ventilation rate on deposition velocity was considered, compared with a constant deposition velocity. The required clean air delivery rate (CADR) for the air cleaner might be underestimated if the influence of natural ventilation rate on deposition velocity was not considered. Therefore, the dependence of PM2.5 deposition velocity on natural ventilation rate should be considered in PM2.5 infiltration factor calculation, I/O ratio prediction, and air cleaner selection. 

Bian, Y., Wang, R., Wang, S., Yao, C., Ren, W., Chen, C.*, Zhang, L.* (2018). Metal-organic frameworks-based nanofiber filters for effective indoor air quality control. Journal of Materials Chemistry A, 6, 15807-15814. (Particle filtration, Particulate matter, Building)

Indoor air quality is essential to public health as people spend most of their time indoors. Hence, effective indoor air filtering is under heavy demand to deal with this challenge. Metal–organic frameworks (MOFs) have been demonstrated as suitable candidates for air pollution control because of their unique properties, such as large surface area and rich functionalities. The integration of MOFs into an organic polymer matrix is considered to be an effective method to control air pollution; however, an efficient and low-cost method to fabricate such filters is still lacking. Herein, an immersion method was proposed for embedding the homogenous growth of MOFs into nanofibers with a superior capability of wind resistance without film failure. The prepared MOF-filter shows effective PM2.5 and formaldehyde removal. The PM2.5 filtration efficiency increased from 74.5% to 87.2% after integrating ZIF-67 nanocrystals into the electrospun PAN nanofibers. Moreover, the PM2.5 filtration efficiency remains at more than 99% during a long-term test over 30 days. The ZIF-67@PAN filter also achieves a formaldehyde removal efficiency of 84%. This work not only proposes a scalable and low-cost method for fabricating flexible MOF-nanofiber filters but also holds great promise for improving indoor air quality and reducing the associated health risks. 

2017 Particle