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Edit by Guy Kuo

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[title] Fans Tested
[* black] Typical, small tubaxial fans lack sufficient static pressure capability for use in the Fan HALO configuration. We are drawing air in ''through'' a viral filter. Static pressure capability is vital, but we must also balance against filter flow limits.
[* black] Blower style fan yields much better performance than tubaxials. I use this 51 mm blower from https://www.digikey.com/product-detail/en/nmb-technologies-corporation/BM5115-04W-B50-L00/P15682-ND
[* black] NMB Technlogies BM5115-04W-B50-L00 blower fan with 3.5 CFM (0.098m³/min), but higher static pressure of 0.803 in H2O (200.0 Pa) provides ample airflow and pressure with a single air intake filter and two expiratory flutter valves.
[* icon_note] Max CFM rating might seem too high, but remember that is ''without'' back pressure. With resistance of filter and flutter valves, actual flow rate is much lower, about 20 l/min.
[* icon_caution] PLEASE DO NOT HORDE FANS. Only obtain the number you will actually ''deploy'' to providers. Hording deprives others in need during this COVID-10COVID-19 crisis.
[* black] Other blower fans may yield more ideal combination of power draw, static pressure, flow rate, noise, and availability, but I am limited in project prototyping budgetavailability. 150 to 250 Pa static pressure capability is likely best range. Fans in the upper end of range may require reductionchange to a single flutter valve to control flow rate.
[* black] These alternative fans are good candidates, but I have not yet tested them...them. If you change fan model, verify CO2 levels via gas sampling
[* icon_caution] PLEASE DO NOT HORDE FANS. Only obtain the number you will actually ''deploy'' to providers. Hording deprives others in need during this COVID-10COVID-19 crisis.
[* black] Other blower fans may yield more ideal combination of power draw, static pressure, flow rate, noise, and availability, but I am limited in project prototyping budgetavailability. 150 to 250 Pa static pressure capability is likely best range. Fans in the upper end of range may require reductionchange to a single flutter valve to control flow rate.
[* black] These alternative fans are good candidates, but I have not yet tested them...them. If you change fan model, verify CO2 levels via gas sampling
[* icon_note] https://www.digikey.com/product-detail/en/sunon-fans/MF50151VX-B00U-A99/259-1829-ND/7691033 https://www.digikey.com/product-detail/en/sanyo-denki-america-inc/109BC12GC7-1/1688-1035-ND/6191751 https://www.digikey.com/product-detail/en/cui-devices/CBM-5020V-148/102-5585-ND/7623146