Distribution characteristics, growth, reproduction and transmission modes and control strategies for microbial contamination in HVAC systems: A literature review

In this study, we investigated the effects of environmental factors such as airflow velocity, relative humidity (RH), temperature, and duct reflectance on the performance of in‐duct UVC lamps. Staphylococcus epidermidis, Pseudomonas alcaligenes, and Escherichia coli were used as the test bacteria. The UV irradiance, disinfection efficacy, and UV susceptibility constant (Z value) of the test bacteria were experimentally determined. The results showed that the UV disinfection efficacy decreased as the airflow velocity and RH increased. The maximum UV disinfection efficacy was obtained at temperature of 20‐21°C compared with the performance at lower temperature (15‐16°C) and higher temperature (25‐26°C). When the RH increased from 50% to 90%, the Z values of airborne bacteria reduced by 40%, 60%, and 38% for S epidermidis, P alcaligenes, and E coli, respectively. Besides, susceptibility constants had lower values under both cooling temperature (15‐16°C) and heating temperature (25‐26°C) compared with that under the temperature of 20‐21°C. It was observed that S epidermidis generally had the highest resistance to the UV irradiance. The results also showed that the UV disinfection efficacy was lower in the duct with a black surface than in the clean duct.

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“…maintenance. 1 Such bacterial contamination not only decreases the filtration efficiency but also contaminates the filtered air.…”

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confidence: 99%

Disinfection by in‐duct ultraviolet lamps under different environmental conditions in turbulent airflows

et al. 2020

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“…So, the microbial communities in the air purifier are regional. Moreover, limited studies were carried out on the microbial community in HEPA filter in an air purifier, while most focused on microbes in HVAC filter 24,[27][28][29][30][31] . Knowledge of microbes in HEPA filter in office was also lacked, except the concentration and the size distribution of microbes 32 .…”

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Bacterial community analysis of floor dust and HEPA filters in air purifiers used in office rooms in ILAS, Beijing

Guo

Xiong

Kang

et al. 2020

Sci Rep

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Air purifiers with high-efficiency particulate air (HEPA) filters remove not only particulate matter but also airborne microorganisms in indoor environments. We investigated the bacterial community in HEPA filters (used for 1 year) and that in the floor dust of 12 office rooms in Beijing. We found that the viable bacteria proportion in the filter was significantly higher than that in the floor dust (p < 0.001). The Non-Metric Multi-Dimensional Scaling analysis showed that the bacterial communities in the filters and dust were significantly different (p = 0.001). The Chao1, Shannon-Wiener and phylogenetic diversity values in the filter were significantly higher than those in the dust (p < 0.001). The predominant bacterial classes in the filter were Alphaproteobacteria and Actinobacteria, whereas those in the dust were Bacteroidia, Clostridia and Bacilli. Human occupancy contributed more to the bacterial community in the filter than that in the dust. Klebsiella and Alloprevotella in the dust and filters positively correlated with the occupancy density. Soil bacteria contributed to a significantly higher proportion of the bacteria in the HEPA filter (p < 0.001). In contrast, human oral, indoor air and outdoor haze contributed to a higher proportion of the bacteria in the dust samples (p < 0.001, p < 0.01 and p < 0.05, respectively). As HEPA filters serve as an ecological niche for indoor bacteria, they should be carefully investigated during the assessment of indoor environmental health. People spend the majority of their time indoors, wherein air pollution levels highly correlate with outdoor pollution levels 1-6. In recent years, haze pollution, fine particulate matter (PM) in particular, has been reported to increase human mortality rates owing to the development of heart disease 7,8 , stroke, respiratory disease 9 and lung cancer 10,11. The level of air pollution in China is substantially higher than in many developed countries 12. Moreover, its threat to public health has become a serious concern, particularly concerning haze events 13. Thus, an effective technology is essential for the removal of PM from indoor environments during periods of haze. To this end, air purifiers with high-efficiency particulate air (HEPA) filters are widely used in the indoor environment, particularly in areas with heavy haze 14. People are exposed to various microbes in indoor environments. Many factors could affect indoor microbial composition, including human occupancy, occupant behavior, pets and outdoor environment 15-18. The air purifier was mainly used to remove indoor PM, partly comprising microorganisms. Microbes in the air could be transmitted to the HEPA filter in the air purifier. Suzuki et al. (2003) collected swab samples from the air purifier filters in the houses of seven healthy children with varicella. They found the varicella-zoster virus was detected in 29% of filters in air purifiers by day 3 19. Furthermore, Maus et al. (2001) studied the effect of the filters on the viability of microbes. They reported microb...

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“…For many general premises, it is not economically feasible to apply high ventilation rates or use high‐efficiency particulate air (HEPA) filters . Considering the adverse implication of exposure to indoor airborne pathogens on human health, there is a huge demand for efficient indoor air disinfection technologies …”

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confidence: 99%

Comparison of disinfection performance of UVC‐LED and conventional upper‐room UVGI systems

2019

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We developed a novel, compact upper‐room ultraviolet germicidal irradiation system with light‐emitting diode sources (UR‐UVGI‐LED) to enhance the disinfection of bioaerosols in an enclosed room space. Its effectiveness was evaluated and compared with the conventional upper‐room ultraviolet germicidal irradiation system with mercury vapor sources (UR‐UVGI‐MV). Escherichia coli, Serratia marcescens, and Staphylococcus epidermidis were atomized under the well‐mixed condition and exposed to UR‐UVGI‐LED (or UR‐UVGI‐MV) device. The intensity output of the UR‐UVGI‐LED was also varied from 0% (no LED), 25%, 50% to 100% to further evaluate the UR‐UVGI‐LED disinfection effectiveness under different power levels. The decay rates for UR‐UVGI‐LED ranged from −0.1420 ± 0.04 min−1 to −0.3331 ± 0.07 min−1 for Escherichia coli, −0.1288 ± 0.01 min−1 to −0.3583 ± 0.02 min−1 for Serratia marcescens, and −0.0330 ± 0.01 min−1 to −0.0487 ± 0.01 min−1 for Staphylococcus epidermidis. It was noticed that the intensity level had a non‐linear influence on the UR‐UVGI‐LED’s performance. The decay rates achieved by the UR‐UVGI‐MV system were −0.3867 ± 0.08 min−1, −0.4745 ± 0.002 min−1, and −0.1624 ± 0.02 min−1 for Escherichia coli, Serratia marcescens, and Staphylococcus epidermidis, respectively. Hence, the disinfection performance of both UR‐UVGI‐LED and UR‐UVGI‐MV systems was comparable for Escherichia coli and Serratia marcescens. These results demonstrate that the UR‐UVGI‐LED system has a high potential to be used as a safe and effective irradiated light source to disinfect indoor airborne pathogens.

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Distribution characteristics, growth, reproduction and transmission modes and control strategies for microbial contamination in HVAC systems: A literature review

Cited by 104 publications

References 121 publications

Disinfection by in‐duct ultraviolet lamps under different environmental conditions in turbulent airflows

Disinfection by in‐duct ultraviolet lamps under different environmental conditions in turbulent airflows

Bacterial community analysis of floor dust and HEPA filters in air purifiers used in office rooms in ILAS, Beijing

Comparison of disinfection performance of UVC‐LED and conventional upper‐room UVGI systems

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