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Ultraviolet Germicidal Irradiation in Educational Facilities

As the 21st century continues to unfold, it has witnessed the widespread growth of the COVID-19 epidemic virus across the world spelling disaster for large groups of people in various types of facilities, ranging from Health care to commercial ones; Educational facilities focal centers for disease transmission, as a result, encounter dire consequences as well. Educational facilities are basically classified into five types for children and students as follows:
Because young people’s concentration is almost in classes, it causes cross-infection when even a single child comes to school with an infection such as a cold or the flu. Consequently, children who attend school bring home contagious infections which are then transmitted to family members, thereby continuing the process of epidemic spread in the community. To address this problem, Ultraviolet Germicidal Irradiation (UVGI) has been proven to be an effective measure
It should be taken to the concentration that each type of educational facility and age group is subject to particular types of infections, and this should be considered while designing a UVGI system. For example, daycare centers or nursery schools are commonly subject to high rates of Adenovirus, Echovirus, and Rhinovirus while Colleges and Universities are commonly subject to outbreaks caused by Adenovirus, Bordetella, Chlamydia, Influenza, Mycoplasma, Parainfluenza, Neisseria, and Streptococcus. Meanwhile, the Majority of microbes are susceptible to UV disinfection in air and on surfaces; therefore, by utilizing the UVGI system in such areas concentration of microbes can be significantly reduced.

How UVGI works

It has been verified that UVG disinfects specific pathogens in laboratory experimentation. By destroying the DNA of microorganisms, UVGI could inactivate and stop the reproduction of the pathogens. All viruses and almost all bacteria are vulnerable to moderate levels of UVGI exposure, but the magnitude of the effect is species-dependent. Ultraviolet rays with wavelengths shorter than 300 nanometers (nm) are extremely effective in killing microorganisms. The main germicidal band; in other words, is within the C bandwidth (UV-C) ranging from 200nm to 280nm. The cell membranes and DNA break down when exposed to high intensity UV at 253.7nm. This is the process through which short-wave ultraviolet light can disinfect liquids, surfaces and indoor air. The effectiveness of UV-C is directly related to intensity and exposure time. In addition, environmental factors like humidity, airborne mechanical particles and distance can also affect the performance of the UV fixtures; thus, for reaching best conclusion each project condition should be scrutinized with painstaking attention when UVGI system is picked and designed.
Upper room and in-duct UVGI are the most conventional UVGI systems types installed in educational facilities. In the rest of this article, we will investigate two case studies (one for each method of UVGI system installation) and will discuss their results.

Case Study 1

Case Study of Upper-Room UVGI in Densely-Occupied Elementary Classrooms by Real-Time Fluorescent Bioaerosol Measurements, Chunxiao Su, Josephine Lau, and Fang Yu, 2017
This study evaluated the reduction of bioaerosols counts by using an upper-room UVGI in classrooms of an elementary school, as an example of densely populated indoor area. The experiment has been done in 20 days over a 4-months period. The researchers compared the count of bioaerosols in two different sets of classrooms: UVGI group and non-UVGI group; to quantify the difference between the two. The results of this study are summarized as follows:
Upper room UVGI
■ Upper-room UVGI devices can reduce the bioaerosols found in an elementary classroom. Daily samples collected from the control classroom were statistically significantly higher than those from the classroom equipped with UVGI devices. The figure below shows the difference between the two groups in consecutive months.
Comparing the concentrations from occupied and unoccupied periods found significantly higher pathogens count during the occupied periods of all visiting days. This result supports the notion that humans and their activities are the primary cause of an increase of detectable pathogens during occupied periods.

In-duct UVGI

Case Study 1

Advanced HVAC Systems for Improving Indoor Environmental Quality and Energy Performance of California K-12 Schools, Report by California Energy Commission (CEC), 2006

■ Total fungal and bacteria colonies on cooling coil surfaces were reduced by 65–100%
■ The system air flow and efficiency did improve, but was not statistically significant due to sample size and testing conditions
■ The success of the technology is dependent upon the quality of the installation. Review and inspection of installation will help assure quality.
Combining coil disinfection with air disinfection is recommended for maximum effectiveness.

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