Presentation of the results of the spatial lift filter study

When using a room air fil­ter from MANN+HUMMEL, Heil­bronn Uni­ver­si­ty (HHN) demon­strates a reduc­tion in aerosol par­ti­cle con­cen­tra­tion of up to 90% with the rec­om­mend­ed set­ting and best pos­si­ble instal­la­tion. The research team led by Pro­fes­sor Jen­nifer Niess­ner and Prof. Dr. Raoul Zöll­ner inves­ti­gat­ed the rel­a­tive risk of infec­tion explic­it­ly at the points where stu­dents inhale, rely­ing on a low-cost sen­sor net­work and flow simulations.

Indoor air puri­fiers are con­tro­ver­sial as a means of con­tain­ing the SARS-CoV2 pan­dem­ic for schools and uni­ver­si­ties. One of the main routes of trans­mis­sion for SARS-CoV­‑2 virus­es are tiny air­borne droplets called “aerosols” that are emit­ted when peo­ple breathe, talk, sneeze, cough, and sing. Mobile room air fil­ters aim to reduce the indi­rect risk of infec­tion by remov­ing aerosol par­ti­cles. How­ev­er, it has not yet been clear what role the posi­tion and ori­en­ta­tion of a room air fil­ter has, whether these devices always lead to a sim­i­lar reduc­tion in infec­tion risk at all posi­tions, or pos­si­bly increase it local­ly in spe­cial cases.

HHN Pro­fes­sor Niess­ner and her team inves­ti­gat­ed the effec­tive­ness of the OurAir SQ 2500 room air fil­ter, which was pro­vid­ed by MANN+HUMMEL. The occu­pied seats in the test lec­ture hall, the loca­tion of the “infect­ed”, the instal­la­tion loca­tion and the ori­en­ta­tion of the room air clean­er as well as the vol­ume flow of the room air clean­er were var­ied and the tem­per­a­ture and the rel­a­tive humid­i­ty were examined.

Mea­sure­ments and flow sim­u­la­tions were used for this pur­pose. A peri­od of time was con­sid­ered, con­sist­ing of a com­bi­na­tion of 20 min with a run­ning par­ti­cle gen­er­a­tor and 20 min with­out par­ti­cle gen­er­a­tion. Even with an unfa­vor­able posi­tion and ori­en­ta­tion of the room air clean­er, the par­ti­cle con­cen­tra­tion is reduced by approx. 60 % on aver­age. How­ev­er, care must be tak­en to ensure that the direc­tion of dis­charge does not allow par­ti­cles to be trans­port­ed from per­son to per­son. With a good set-up posi­tion, local reduc­tions of up to 90% are mea­sured in this com­bined scenario.

The device was set up in a step audi­to­ri­um of the HHN, Cam­pus Son­theim (room E116). Card­board box­es with light bulbs served as dum­mies for peo­ple to sim­u­late a real heat­ing sit­u­a­tion and a real flow obsta­cle. One of these dum­mies was equipped with an aerosol gen­er­a­tor and emit­ted harm­less salt spray. The team deter­mined the aerosol par­ti­cle con­cen­tra­tion, and thus the risk of infec­tion, using high-accu­ra­cy opti­cal par­ti­cle coun­ters and a net­work of low-cost par­ti­cle sen­sors placed in the “face” of the dum­mies, i.e., the loca­tions of poten­tial inhalation.

“The study results show that indoor air fil­ters can help reduce the risk of infec­tion in enclosed spaces and can be an effec­tive com­po­nent of pan­dem­ic response for schools or uni­ver­si­ties, for example.”

- Pro­fes­sor Jen­nifer Niessner

The results of the indoor air fil­ter study are being incor­po­rat­ed into the col­lab­o­ra­tive research project “Test aerosols and meth­ods for effi­ca­cy stud­ies of air purifi­ca­tion tech­nolo­gies against Sars-CoV­‑2.”
Niess­ner is coop­er­at­ing here with col­leagues from the Uni­ver­si­ty of Stuttgart, the Karl­sruhe Insti­tute of Tech­nol­o­gy (KIT) and the Uni­ver­si­ty Hos­pi­tal of Tübingen.

The aim of this project is to inves­ti­gate the appli­ca­tion, char­ac­ter­i­za­tion and sam­pling of test aerosols, to check whether analo­gies from sur­ro­gate virus­es to SARS-CoV­‑2 are per­mis­si­ble and to find out how dif­fer­ent para­me­ters and spa­tial con­di­tions influ­ence the effec­tive­ness of air purifi­ca­tion devices.

Heilbronn University — Competence in Technology, Business and Computer Science

With approx­i­mate­ly 8,200 stu­dents, Heil­bronn Uni­ver­si­ty is one of the largest uni­ver­si­ties of applied sci­ences in Baden-Württemberg.
Its com­pe­tence focus is on the fields of tech­nol­o­gy, busi­ness and com­put­er sci­ence. At four loca­tions in Heil­bronn, Heilbronn-Sontheim,
Künzel­sau and Schwäbisch Hall, the uni­ver­si­ty offers more than 50 bach­e­lor’s and mas­ter’s degree pro­grams. The uni­ver­si­ty main­tains close coop­er­a­tion with com­pa­nies from the region and is thus very strong­ly net­worked in teach­ing, research and practice.