Moving air "without sound".

The big quiet fan moves far more air with far less noise across pressures in the 10 pascal range, than any other fan in the world, by far.   In many common environments it is actually inaudible and has been described as "without sound", while moving enough air across a set of filters to mostly protect a whole room of people from airborne disease, or particulate pollution of other kinds. 

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 costly with current on-market solutions, 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.   A CR box can be built with it, by just taping together filters.  This is the main intended use for the near future, but I have also done some design work for a "reference design" (except that it's not really done) for an air purifier that gives as much clean air per minute at the same noise level as about $5000 worth of the next best HEPA machine on the market (the Blast MKII, HEPA is actually not the best idea btw).  And yet it costs only about $500 in parts and labor, if the fan is $200 (see BQAP link on the top of this page).  By this, I mean that if you turn the blast MKII down to a level where it gets a CADR to noise ratio that is the same as the latest and best BQAP, then divide the CADR of the BQAP by the CADR that that machine gets, and multiply by the retail price of the Blast MKII, you get about $5000 CAD.  This is approximate, it could be more or less depending on the details, and does not include tax and shipping.

Total cost per cubic meter of clean air for a typical CR box made with a BQF, below 42 dBa for all compared machine sets (multiple machines are needed, each turned down, aside from the BQF machine), is approximately 1/8.5 times that of the best PC fan air purifiers, about 1/16 that of the most economical off the shelf HEPA machine I have been able to find (the Blast MKII), and indeed, discarding the noise limit, approximately a third that of even the infamous CR box on maximal power (which is of course is much louder than 42 dBa, about 64), which given it's extreme cheapness, you would think would be king.  Because the BQF uses the filters better, and takes less electricity, it actually is cheaper still, while at the same time being far quieter.

Note: I feel bad for picking on the Blask MKII, but to be clear I am doing that because it's the best machine I know of for this purpose.  Why bother with anything but the best?  The manufacturers seem to be great people, no criticism is intended. It's a great machine.

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 41.6 dBa at 400 rpm (1450 CFM in the same context.  Unimpeded flow has been measured at about 1750 CFM at 400 rpm).  The mass produced version will have a top speed of between 410 and 425 RPM.

To put in perspective the sound intensity the machine produces, 35 dBa SPL at 1 meter distance, 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.  

The character of the  noise of the fan is also very good, with no hum or buzz (tonal noise), for the latest prototypes.

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.  It's not just that the design and code is available, it's also adapted in many ways in coherence with the general open source ethos - no planned obsolescence is designed in, for instance, although there is always some in the lower level components.   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.

The crowdfunding wasn't working out very well, I may pick it up again another time.  The near term plan is to just produce kits, and then improve the production process over time by using injection molding instead of additive manufacture, improving techniques, etc, one part at a time, starting with the parts where this delivers the most benefit.  Then an assembly service will eventually also be offered, an approach pioneered by others and already used in the clean air community for some things like PC fan boxes.  

 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), and Adenovirus (also similar to a cold and quite common) from the air before they can cause disease, for mere pennies per infection prevented, in the right circumstances.   10 liters per second CADR (21 cfm) per person gave about 80% reduction in infection rates, so it works pretty well, even factoring in near field transmission (1).  A BQF with suitable filters can give about 1000 cfm CADR, so enough to chop transmission by 80% for 50 people (a bit more with better filter sets, the record is about 1200).  >1000 cfm plus entrained air mixing tends to break up near field transmission some in a room the size of a classroom.

  I have tested and proven that machines that can be built with the BQF are dramatically superior, providing more than ten times the cubic meters of 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, NorthBox, the Tempest and similar machines are much better and cheaper than bog standard HEPA machines and are not really in competition, they are smaller format machines, this is a big one.    For large capacity, a machine made with the BQF is also more practical in other ways, including lifespan, running cost, and size of the set of equipment.

In general we can actually consider the pressure-flow rate and noise relationship of the PC fans, which are the next best option for these parameters, and the BQF, and draw an equivalency.  We can draw an equivalency because if you turn a fan down, it's pressure-flow-noise relationship improves, but at the cost of less overal flow.  It is possible that some fans cannot be compared because the static pressure of one is lower than the operating pressure of another in some region.  However that is not the case here. If we look at the flow at 10 pascals, a typical pressure for a filter box, it takes about 46 p14 fans, all turned down to an absurdly low RPM, to move the same air across that pressure at the same noise output as a BQF.  This calculation is imprecise as dBa figures change considerably from error, a 3 dB error is minor and yet represents a factor of 2 in total noise energy.   The cost of the fans is higher anyway, and unless you get the ball bearings (which invariably costs even more although I don't think it fundamentally has to much) then they don't last very long, the hydraulic bearings only last 1.5-2 years continous operation.  If one of the 46 fans fails, air tends to go backwards through it.  You have to mount all those fans, add finger guards to them, wire them all, and interface them all to filters, all of which are more complex and costly than their equivalent with one single larger diameter fan.  In general it is clear that for large scale deployment of air cleaning power, we should not be confining ourselves to large numbers of these small fans.  

Pc fans with standard filters are a good step forward and are still fine for smaller format machines, but it's time to move beyond small format machines and ensure clean air for all people at all times in all spaces at a large scale, and the BQF is a very good start on that.

References:

(1)https://pmc.ncbi.nlm.nih.gov/articles/PMC9787545/  Increasing ventilation reduces SARS-CoV-2 airborne transmission in schools: A retrospective cohort study in Italy's Marche region