Moving air "without sound".

The big quiet fan moves far more air with far less noise than box fans, and gets considerably higher flow to noise ratio than even the best PC fans.  In many common environments it is actually inaudible and has been described as "without sound". 

The "killer app" for this fan is air purifiers for use in classrooms, offices and other spaces where quiet is important yet large amounts of clean air is needed.  There is a new engineering standard to change building ventilation after the lessons learned from the airborne disease pandemic, called ASHRAE 241.  It specifies about 2.7 times more clean air than the previous building standards.  There are also limits on noise, such as ANSI S12.60, which specifies noise limits in classrooms.  Hospitals and other spaces have similar standards.  COVID-19 is transmitted primarily through the air on small particles that hang like smoke in the air, not droplets.  Clean air is the best solution.  There are also many other reasons to clean the air.

To meet both these standards at once is extremely hard, and the Big Quiet Fan can be used to make an air purifier which meets this need, when practically nothing else in a reasonable price range will.   I have done the design work for a "reference design" for an air purifier that gives as much clean air at the same noise level as about $5000 worth of the next best air cleaner on the market (the Blast MKII).  And yet it costs only about $500 in parts and labor, if the fan is $200. (see www.bqap.ca.)

The best prototypes so far produce about 35 dBa at 1 meter distance, at 300 RPM (1110 cfm flow in the case of the largest of the air purifiers shown below) and 43.5 dBa at 400 rpm (1450 CFM in the same context.  Unimpeded flow has been measured at about 1750 CFM at 400 rpm).  Higher RPMs may be possible with the eventual mass produced version.

To put in perspective the amount of sound energy the machine produces, 35 dBa is nearly the same noise as a single P14 fan, which is one of the quietest PC fans available today.  The entire BQF, moving at 300 rpm and transporting 1110 CFM across MERV-13 filters, actually makes nearly the same amount of noise as a single P14 fan.  ~43 dBa would be about 8-10 of the P14 PC fans, approximately.  And yet it moves more than triple the air, costs less, is more reliable and also practical in many ways.

The character of the  noise of the fan is also very good, with no hum or buzz (tonal noise), except for the very small amount of motor hum I'm still working on.  From the blades, there is just a gentle whoosh.

The fan and reference design are both fully and deeply open source, MIT license, so free to use for anything by anyone, even for profit or for proprietary derivatives.  This is part of a different production paradigm, proving open source hardware works and works well.  Most business people don't like this idea, however it makes sense in many ways when you look into the details.

There will be a crowdfunding campaign to get pre-orders and raise capital to produce them in large numbers at low cost, and get them UL listed, and otherwise certified for safety.  For now they are all 3D printed on a large 3D printer.   I can make many like this, but thousands is not practical.  We need thousands to get out there.

The fan will be good for a great many things, including use as a whole house fan, window mounted fan during hot weather, a circulator fan, and more. 

 Air purifiers can remove pathogens such as SARS-Cov-2 (COVID-19), regular flu, colds, whooping cough and RSV (much like a cold, and very common), from the air before they can cause disease, for mere pennies per infection prevented, in the right circumstances.   They can chop infection rates in a space by more than 80%.

  I have tested and proven that machines that can be built with the BQF are dramatically superior, providing more than ten times the clean air per dollar as the next best HEPA purifier machines currently on the market at the same noise level, and many times again the clean air per dollar of typical machines. Clean Air Kits and NorthBox machines are much better and cheaper than bog standard HEPA machines,  but BQF based machines are still about 2.5-3 times higher clean air delivery rate at the same noise, than even pc fan based machines, when you need >500 CFM CADR capacity or thereabouts.  For large capacity values, a machine made with the BQF is also more practical in other ways, including lifespan, running cost, and size of the set of equipment.

  The resulting machine can be 1/3-1/4 the total size of an equipment set that provides the same clean air delivery rate at the same noise level, and also have much lower upfront cost for the same clean air delivery rate.

It can be substituted in place of the common box fans such as the Lasko 3733, in "CR boxes", also known as filter boxes, to produce a machine which has 3-4 times the clean air delivery rate, with much less noise than the lowest speed setting of the box fans (which I measured at 50 dBa, max speed is 64 dBa on the Lasko 3733) , and yet with a total machine cost that is only slightly higher, if we can hit the goals of <$140 USD per fan sale price, including delivery.