While this design still works, the box fan is still hard to source. There's a newer and improved approach to use multiple PC fans powered by a 12V or 5V power supply which show silent opeation and good CADR. See here for an example https://www.cleanairkits.com
- What is a Corsi-Rosenthal box / Comparetto Cube?
- Bill of materials
- Building instructions
- Noise
- Effectiveness
It's a DYI Air cleaner that can be built rather inexpensively, and have been proven to significantly reduce airborne particles (such as SARS-CoV-2 carrying droplets and aerosols).
Read more about it, how to build it, etc... here:
https://encycla.com/Corsi-Rosenthal_Cube
https://cleanaircrew.org/boxfanfilterfaq/
Materials add up to about ~120 EUR per cube.
The original building instructions are based on 20 inch box fans. There are not many 50 cm / 20 inch box fans on the market in Germany. I found the following one offered by Sichler Hausgeräte:
http://www.sichler-haushaltsgeraete.com/Extrastarker-Bodenventilator-3-Stufen-NX-6414-919.shtml
(It is being sold by Pearl for about ~60 EUR)
Power consumption: 60 Watts Air Flow: 50,26 m³/Min.
Germany (and other european countries) use ISO 16890 to rate air filters compared to ASHRAE/MERV used in the US. Roughly comparable to MERV-13 is ISO16890 ePM1 which filter at >50% of particulate matter sized 0.3 - 1 micrometers. The previous (now obsolete) standard EN779:2012 equivalent is F7.
Z-Line filters are available from different sources (search for "Z-Line F7" or "Z-Line epm1"). I found the following for about 15 EUR/filter (sized 495mm x 495mm x 48mm, about 20 inch x 20 inch x 2 inch):
https://htm-shop.de/filterzelle-z-line-f7-iso-epm1/fz-02-1005-634
Cardboard, adhesive tape.
Check the Construction Guide for details.
The filters are directional, three's a soft fuzzy outside and a structured inside. An arrow on the label indicates the air flow direction.
Filter Outside
Filter Inside
Direction Label
Arrange all filters so that the airflow points inwards:
Fixate them with a bit of adhesive tape
Cut out cardboard for the bottom
Use the adhesive tape to seal the sides and bottom airtight
Mount the fan on the box, blowing upward
The space at the edge can be used to pass through the power cord
Mount the fan and seal it with adhesive tape.
The airflow only takes place in the middle (tested using tissue paper)- this calls for a fan shroud.
Measured from the center, the airflow happens in a circle of about 18 cm radius. Cut out a fan shroud of the appropriate size and place it on the fan. Seal it with adhesive tape.
At its highest setting, at about 1m distance I measure about 56 dB using the most sophisticated measurement device I have available.
At the medium setting, I measure about 49 dB in 1m distance and 47 dB at 2m distance.
I don't have access to any measurement device to measure the airflow to calculate CADR.
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