AMCA (Air Movement and Control Association ), recently commissioned a simulation study presenting how the operation of circulating fans within warehouses may impact airborne particle and aerosol transmission. The purpose of the study was to improve the body of Covid 19 guidance in relation to circulating fan use and operation.
The principle investigator of the study was Dr. Liangzhu (Leon) Wang, PhD, PE, who is also an Associate Professor of Concordia University’s Department of Building, Civil and Environmental Engineering. Dr. Wang was assisted by a several other research scientist, engineers and other industry professionals(a full list can be found within the study details, the full study can be downloaded at https://users.encs.concordia.ca/~leonwang/moodle/mod/forum/discuss.php?d=13 ).
The building used for the simulation measured 330ft x 150ft x 28ft with two large diameter ceiling fans installed 120ft apart. The simulation assumed the warehouse location was in Chicago IL. There were a wide variety of layout configurations simulated in regards to worker line locations, fan air speeds and worker orientation. The results gained from the study are applicable to a wide range of industrial type facilities. (Download the full study at https://users.encs.concordia.ca/~leonwang/moodle/mod/forum/discuss.php?d=13 )
Summary of Conclusions
Operating a fan at the highest speed in the downward direction produces the most favorable results (creating the greatest amount of dilution)
During the winter months, operating a fan at high speed in a downward direction may create too much draft for employees. It’s very common to run ceiling mounted fans in a reverse direction during the winter months. This study found reversing fans at the highest speed reduces the performance compared to running the fan in the downward direction.
Reversing fans at slower speeds may further reduce the diluting effect and the warehouse concentration could become higher.
Fan Operation Recommendations (For Mitigation of Airborne/Aerosol Transmission)
- Summer Fan Operation – Operate fans in a downward direction and at the highest speed setting..
- Winter Fan Operation – Operate fans at highest speed possible while limiting drafts as much as possible(keeping in mind higher speeds show increased effectiveness).