In October 2020, the Ministry of Science established the “Body of Experts Aerosols”. More than 10 scientists from various disciplines research how the risk of an infection with SARS-CoV-2 in closed rooms can be reduced. The body of experts investigates the extent to which particle concentrations in enclosed indoor spaces can decreased with the help of highly effective indoor filters.
To weigh up the most effective methods, the Ernst-Abbe-Hochschule Jena, University of Applied Sciences participated and investigated active filtering and exchange of room air using a mobile air conditioning unit to prevent infection with the SARS-CoV-2 virus.
The complete report with all results is available free of charge [German language].
Further information on the study as well as videos of the experiments [German language] are available at https://www.simmi-bleifrei.de/sonstige-dinge/ .
Closed interior rooms are a bigger problem in winter
Closed indoor spaces in schools, universities and music schools are a problem, especially in winter, when cold temperatures limit the ability to air rooms. One way to allow facilities to operate normally despite the restrictions is to filter and actively exchange the air. A tracer washout experiment will be conducted to show whether and how well it is possible to achieve this with a mobile air conditioning unit.
A mobile air conditioning unit and a swivel fan were used to prevent aerosol clouds in the room. They actively circulate the room air and assist in the circulation process, respectively. To investigate the washout process, disco fog and thus a fog machine were used as a measurable tracer medium.
The TRDA 2.0 measuring instrument with a 1.5 m light measuring section from NETZSCH TAURUS Instruments GmbH determines the relative light transmission in a defined room. Here, it was used to measure the relative smoke density or, in this case, the density of fog.
The original purpose of the test device is the determination of the smoke production of materials during thermal decomposition in accordance with DIN 50055. It is therefore ideally suited for the objective determination of the density of disco fog in the room and was made available to the University of Applied Sciences Jena for the duration of the investigations.
Investigated parameters of the experiment
The following values were considered for the investigation:
Air exchange rate (n) = How often is the air in a room renewed by fresh air within one hour?
Air filtration rate (f) = How often is the air in the room circulated and filtered?
Within three days, experiments were conducted in three rooms of different sizes (room 1: 18m3, room 2: 120m3, room 3: 220m3).
Figure 2 shows that the air volume (fog) in the room with 18m3 was completely washed out within t<15 min. In the process, the air volume was exchanged about 20 times (f = 20 / h). Similarly, the following results are obtained for the other room sizes:
Room 2 with 120m3: After 65 minutes, the fog was completely washed out and the air volume was exchanged somewhat 3 times (f = 3/h).
Room 3 with 220m3: After 83 minutes, the fog was completely washed out and the volume of air was washed out about 1.6 times (f = 1.6 / h).
All details of the test results as well as the modeling of the washout function can be found in the report [German language] here.
Mobile air-conditioning systems are an effective solution to prevent aerosol-clouds and thus infections with SARS-CoV-2 in closed rooms in which active ventilation is not possible. The room air is effectively exchanged, circulated and filtered. This could be demonstrated using disco fog and a smoke density test device. Modeling of the washout time function has to be approximated more accurately by higher mathematical models, since a mixing process of the old and fresh room air has to be considered. Further experiments in classrooms and laboratories during ongoing teaching must also follow this investigation to serve as acceptance tests.
One disadvantage arises from the use of mobile air conditioners in schools and universities: The devices develop a significant amount of noise, which can be disturbing in class. However, there is the clear advantage of air conditioners in summer, as the devices can cool the air in the room by about 2 to 3 °C, which can improve learning success despite the noise. As a temporary solution until large investments of stationary air conditioning units are possible, mobile air conditioning units are therefore an effective solution to avoid aerosol-clouds, to filter the room air and simultaneously achieve a temperature reduction.
About Ernst-Abbe-Hochschule Jena
The Ernst Abbe University of Applied Sciences (EAH) Jena was founded in 1991 as the University of Applied Sciences Jena and was thus one of the first in the new federal states. For some years now, it has not only been Thuringia’s largest university of applied sciences, but also the one with the most research. EAH Jena’s intensive research and development contributes greatly to strengthening Thuringia’s technological potential. Research focuses include precision systems, technologies and materials, health and sustainability, and the cross-sectional field of digitization.