Characterizing the performance of a DIY air filter

Air filtration serves to reduce concentrations of particles in indoor environments. Most standalone, also referred to as portable or in-room, air filtration systems use HEPA filters, and cost generally scales with the clean air delivery rate. A 'do-it-yourself' lower-cost alternative, known as the Corsi-Rosenthal Box, that uses MERV-13 filters coupled with a box fan has been recently proposed, but lacks systematic performance characterization. We have characterized the performance of a five-panel Corsi-Rosenthal air filter. Measurements of size-resolved and overall decay rates of aerosol particles larger than 0.5 microns emitted into rooms of varying size with and without the air filter allowed for determination of the apparent clean air delivery rate, both as a function of size and integrated across particle sizes. The measurements made in the different rooms produced similar results, demonstrating the robustness of the method used. The size-integrated apparent clean air delivery rate increases with fan speed, from about 600 to 850 ft3 min-1 (1019 to 1444 m3 h-1). Overall, our results demonstrate that the Corsi-Rosenthal filter efficiently reduces suspended particle concentrations in indoor environments.

Security Guarantee for Vehicular Message Transmission Based on Dynamic Social Attributes

Effective message forwarding between vehicles can reduce the occurrence of traffic accidents and improve the driving experience. Vehicle clustering can improve message utilization, but attackers in the network pose a serious threat to message forwarding. Based on vehicle clustering, we propose a message forwarding strategy for Vehicular Ad hoc Network. Specifically, the vehicles are clustered based on their directions and speeds. Besides, the friendship of vehicles is evaluated in terms of the interaction friendship and reference friendship. Based on the friendship of vehicles, the optimal vehicle can be selected as the cluster head. Thereafter, the double key technology is designed to encrypt vehicular messages such that the messages can be forwarded more safely and efficiently. The analysis results show that the proposed strategy can effectively improve the message delivery rate, reduce the message leakage rate, and improve the network performance.

Price-performance comparison of HEPA air purifiers and lower-cost MERV 13/14 filters with box fans for filtering out SARS-Cov-2 and other particulate aerosols in indoor community settings

BackgroundSARS-Cov-2 aerosols have potential to accumulate in airspaces of poorly ventilated, indoor spaces such as classrooms, offices, homes, restaurants, and bars. Separately, toxic aerosol pollution (e.g. wildfires, wood burning) is frequently encountered in these locations with ventilation relying on outside air. Portable high efficiency particulate air (HEPA) air purifiers are useful to remove both types of aerosols without relying on outside ventilation. To meet or exceed recommended 4 to 6 air exchanges per hour (ACH), high price-points for select HEPA air purifier models without incurring excessive noise generation make them unaffordable for many households and communities. Do-it-yourself (DIY) alternatives with box-fans and HVAC filters can be much lower cost but their clean air delivery rate (CADR) and noise generation varies greatly depending on choices of filters, number of filters, and fan speeds.ObjectiveTo compare cost-effectiveness and noise-generation of aerosol filtration by commercially available, portable HEPA air purifiers and do-it-yourself (DIY) alternatives built from box fans and HVAC filters rated at MERV 13 or 14 using single and quad filter designs.MethodsThe comparison is based on three metrics: clean air delivery rate (CADR), the noise generated (dBA), and affordability ($$) using an ISO-certified aerosol measurement device to measure input/output particle filtration of particles sizes ranging from 0.3 microns to 10 microns, airspeed meter to measure airflow, and NIOSH sound meter app to measure noise.ResultsAccounting for reduced filtration efficiency of MERV 13/14 filters compared to HEPA, estimated clean air delivery rate (CADR) of a do-it-yourself (DIY) setup using 2” and 4” filters with a box fan running at fan speed 1 for tolerable noise was 278 cfm ($38) to 371 cfm ($58), comparable or better than a commercial HEPA air purifiers running at maximum speed with low noise generation at 282 cfm ($375). However the quad filter designs, popularly known as the Corsi-Rosenthal box, achieved gains in CADR of only 60% over a single filter design but in contrast to 200-250% gains reported by UC-Davis.ConclusionsDIY alternatives using single 1”, 2” and 4” MERV 13/14 filters compare favorably to commercially available systems in terms of estimated CADR and noise but at five to ten times lower cost. Compared to use of one filter, an improvement in CADR (air flow) was observed with a popular DIY configuration involving quad filter design, popularly known as the Corsi-Rosenthal box, not as high as reported by a recent study by UC-Davis