I think you would get better resolution of results if the flap was completely enclosed within the tube so that the air had to push the flap completely out of the way to move through instead of just far enough to jump out the side

My primary thought is to somehow make the measuring arm longer so you can have finer measurements. You're going to have a lot of measurements that are barely off from each other, and your current scale may not be able to show the difference very well. This is a really cool way to do this! I'm in favor of this shift, overall.

Test Engineer here. I think you're going to see a very tight grouping in your results because you have three things going on: 1) As the door opens further, it takes a highly non-linear amount of air flow to push it further. This is because of the reduced flow restriction combined with larger opening. 2) As the door moves to horizontal, the airflow's mechanical advantage is reduced (look at where the force vectors are pointing at 0, 45, and 70deg) 3) As the door becomes closer to parallel with the direction of air flow, the air's ability to impart force is reduced (the sail moves from crosswind to headwind) If you want to measure pressure, you could just use a good ol' analog gauge. They're actually pretty easy to make in addition to being inexpensive to buy.

A proper meter for this would normally have one control orifice, basically having the flap inside of a square tube so it only opens on one side. The current design has the orifice increase exponentially as it opens.

you can use actual water to measure static pressure. Add a U shaped glass pipe at the end of the wind tunel, add water and calibrate:) It will not have any part which can add friction to the equation. Some additional thought: diameter of the pipe can change sensitivity of the sensor.

Your setup currently has nonlinear scale. It can probably be linearized if you add a semi-circular shroud for the door, with a single continuous slot along the bend, so that the amount of air escaping before it can exert pressure on the flap is directly proportional to the flap height. You'd need to manufacture another flap with a counterweight such that its center of gravity lies on the hinge, and drive it closed using a spring. In turn, to avoid the same nonlinear forces problem as with gravity, connect the spring to the flap through a wire and a wheel.

I motion to have the top three of all seasons tested as well, for a more complete set of data. As for another tool to measure the static pressure, use U-pipe Manometers, three of them to be more precise. One measures the differential pressure of zone 1-2, one of 1-ambient the last of 2-ambient. Basically you have enough data to compare since you have the 1-2 one measure the delta directly and with the other two based on the ambient pressure you can check that in case of suction effects occuring.

I like the concept. I’ve always advocated that each fan should be directly compared to the others by max rpm, specific rpm values, and specific decibel values.

this still "measures" air flow through an obstacle (your grid infill). the radial scale could be improved/extended with a linear one so small changes at higher lift result in more noticable results. static pressure would have to be measured before the obstacle - u-shaped tube with water in it, like other suggested.

You may be able to set up a hydraulic static pressure tester by having a water reservoir that the fan blows down into, with an elbow out the side that connects to a vertical, clear acrylic tube with graduations on it. The higher the water rises up the tube from your baseline, the more static pressure you have.

It would be more complicated, but you could mount a mirror (or laser) to the door near its axis and record deflection of a beam. This would allow you to make the deflection angle much larger than a mechanical lever. Or you could use an optical range finder and measure the movements of the door. A potentiometer may be able to do something similar, but I'm less certain of their sensitivity.

The problem i can see with this is that just measuring the angle is going to be more representative of flow rate since the door will open more with more flow. say if you put a tiny fan that had really high sp it would still only open it a tiny amount making it seem like it actually has very little sp. What might be a good idea that could still use this design is to use the flap to push against a set of fine scales and have the flap set to only open to a set position to keep the opening the same size for different fans. And to add to that you could also mount your anemometer inside the box so you could set the opening so each fan was producing the same flow rate and then measure how much force that takes to hold back the flap to get a somewhat normalised flow vs pressure test.

The main issue I would think is as the angle increases the less the flap is in the way meaning it won't be getting the full force

The way is made it's not at all linear making it impossible to compare beyond bigger/smaller. Maybe using more of a lid that lifts straight with a linear spring of some sort. edit: to ckarify, I mean not leaving an opening, which would allow a better pressure reading without airflow/turbulence having an effect.

A lot of people advised to use a U shaped manometer. My two cents to this idea is to use a fluid which has the lowest density as possible. Oil is less dense than water. This can increase the sensitivity of the device.

I like last season's "blowing through a radiator" type of method better, static pressure and air volume are two unserapable parts of a fan's performance as you always have to overcome some kind of resistence in a real life situation, and air is what ultimately takes away the heat so volume matters too. But the concept is nice, even though numbers on the gauge barely mean anything, this device can be useful in comparing fans, maybe add this to last season's test suite. The lower half of the gauge is basically unreachable using ordinary pc fans, as the angle got wider, the contact area will get smaller, and more airflow will just pass by the plate without applying any force or just a little force.

Since you asked, A larger reinforcing grid on the door to lighten it would allow more movement, making the gauge more accurate. I love this concept. It reminds me so much of the wind tunnel the Wright brothers used to design their propellers on their aircraft. Balance weighted and simple, they used the box to design a propeller with an efficiency close to today's standards.

In theory, could get a digital reading with a magnet and a Hall effect sensor. Not sure about repeatability and consistency, though Hall effect sensors are used to great success in flight sticks.

My main concern is that the scale may not be quite linear but more logarithmical in nature since the opening gets larger for a larger scale reading, which alleviates some of the additional pressure.This implies that small differences in the scale readings with regards to high performer fans actually means a greater pressure difference than expected

Hi, I think your solution is pretty good for what you're trying to do. While you were explaining your idea of how to measure static pressure, I visualized a U shaped pipe with the bottom filled water and one end sealed with what you already built so that the air coming out of the fan goes into the pipe. That way the air coming out of the fan would push the water up the open end of the pipe and it should be easy to measure how high the water is pushed. That said, I think it would take some experimenting to find the best diameter of the pipe and it would need to be tall enough so the water doesn't overflow out of the open end. I hope the description makes sense. Love your videos, will see you in the next one.

Interesting idea. Maybe have the flap fully enclosed and sealed with some kind of rubber bracket (or equivalent) on the side facing the fan, then hooked up to a weight scale. Like a food/baking one should be sensitive enough. There's even entirely mechanical ones that you could repurpose. 🙂

Hey, i am using a Sensirion sdp810 differential pressure sensor for a project. it measures 500Pa, communicates over i2c to build a data acquisition system with a microcontroller, it is a very good resolution sensor and not that expensive (35 bucks I guess). but I also like the flap measurement system.

I love the idea and suggestions. You can also clearly see the curve slowing as the fan reaches the top. Makes everything so easy to see.

Hi automotive engineer here, I love your mechanical gage design idea! But I can see a few issues with your measurement. The door flap will not open linearly to the gage. There are two things at play. The door wants to come down, but the force at which it does is related to the angle. The higher it goes, the more the center of gravity is pushed beyond center, and Fg increases exponentially. Also, as the flap opens, the area of the air that can escape is increasing exponentially, too. Your scale drawn is linear, so there could be alignment there. It's hard to calibrate, though. To eliminate the escaping air, you could enclose the flap with like 0.5m of plexiglass. For the angled gravity, you could try a counter balance so that this is perfectly able to rotate freely. I hope this helps.

I think this will work for comparison. But the actual number will be meaningless. You should be able to tell if one is better than another, but not really accurately by what percentage. The resolution might be too low, getting above 10 or so seems nearly impossible, most fans will probably be between 0 and 5. I imagine a lot of fans will be at the same number. You might need a bigger dial with a longer indicator at the top to get a more accurate reading.

Don't know if this would work but. What about using another fan at the end of the pipe and reading the volage generated from air flow.

love the progression of your testing and the tools you're making to test this!

I think what I like the most about this channel is the way people think outside the box and im all for it.

It would be interesting to see the difference of an unimpeded box (without the grid pattern you have to clean up the airflow). I understand why it's there, just curious if it's necessary or not.

Like the idea, much nicer to see this than a number 😀 Also, how does it look with smoke pushed through it 🤔😁

Good job. I like the simplicity and the fact we can make our own.

This is a really cool idea, it's a great way to visualize it, i'm in favor of this! cheers man!

I like it, I wonder if it will be sensitive enough to identify small increments. What was the difference in static pressure measured between the A12 and the Winner of last year in CFM?

I like the box idea, just wish it had more resolution, but I don't know how that could be done. Maybe put a long needle on the end of the gauge and make the gauge circumference bigger. Im also curious on how the "flow straightener" impacts the ability of the fan to lift the door. Can you try one without the flow straightener and one with? That would be easy to design and print.

I've seen suggestions but as I have no idea about this stuff I can't evaluate them. So just want to say, this refresh is a really good idea, always making adjustments to the testing methods, maybe it wouldn't be necessary but for sure it makes the series even more interesting! I'm so happy about this!

To the Author, i think your low rpm test reshiems are fine and don't listen to haters/critical responses, i thought your channel when I first saw it was a little underpowered 😢 but now I see that your low speed tests are very representative of how they would act at high speed (10x's or more) so happy to see your video's and hope to see more from you, i am a sheetmetal worker/engineer that builds my own jet engines from old turbos but have learnt more from your fan testes! Keep up the good work and look forward to more from you 😀😀😀

You could make a tunnel where the fan sits in the middle of it and there is a pitot tube both at the inlet and outlet side. The difference in the pitot tube would give us the pressure difference. 😊

cool test rig, I like the idea of using it along with other testing to create a more complete picture.

EXCELLENT! Now for the micro improvements over time as with any first build.

Oh nice measurement concept, I love it!

As for the manometer a single tube filled with water (or oil for increased displacement) making a U bend and with open ends before and after the load (different thicknesses/style of radiator) would be enough to show the pressure. With a camera and a macro lens against a precision scale you could get quite precise measurement. If you want to you could use some sort of iris with variable aperture (like in a lens) as the load/resistance to create a Pressure/Velocity graph.

How about a load cell attached to the end of a free swinging door with slots around it for air to pass through. Should give you a linear readout of pressure on the door for all wind speeds.

thanks for doing these tests! lots of cool ideas in the comment section, hopefully you can incorporate some of them if they sound legitimate. the engineering is deep!!

I love the idea of using this for the next season! I think the numbering should be modified though, where the gap between units is less as the numbers get higher. Here is my reasoning: To get a fan to go from a 2 to a 4 is pretty easy, where if you were to try to get a fan to go from a 14 to a 16, it will take much more airflow to do so. Therefore, the units should be closer together as they get larger, to help differentiate the top competitors more easily without getting into decimals/fractions. In any event, I would love this to be an equal factor in determining the best fan, along with the traditional methods used prior. Thanks for the awesome content!

I think the angles measured could be not granular enough to differentiate between different fans and you might end up with lots of entries having the "same" result. And even reading the correct value seems pretty prone to error.

You should add a geared indicator so you can have more discrimination between intervals relative to flap displacement angle or a longer indicator tip so you can include more gradations between presently available marks. Your ability to measure differences will likely suffer without something like this.

The wind tunnel is lovely, and those are some nice high quality prints.

This is a good idea. It just needs some refinement. 1) The flap needs to be enclosed in a shroud significantly longer than it is. Right now, you have a lot of spillage that is lowering your results. 2) You need to calculate the moment of inertia of your flap. The effect of static pressure on it is not going to be linear. It is going to vary significantly with the angle. 3) You need to determine the amount of resistance your flow guides impart. Alternatively, if you put an extended shroud on the outlet, they may not be necessary. 4) I would create a second test. Turn your apparatus vertically and create a slightly outwardly sloping shroud. Put a weighted plug at the end that just barely seals where it contacts the apparatus. The static pressure will push up the plug until the pressure maintained under it equals it's weight. The plug should have sloping walls that match the shroud walls. If you know the weight and the elevation change, you can calculate the force applied (F=ma), and from that, the pressure (P=F/A). This would be a simpler design to calibrate, I think. However, it is still not linear because the gap around the edges opens as a function of height since they both slope.

not a bad setup and simplicity is king. while you might have issues keeping it level, maybe find some ultralight linear bearings on some guide rods, blowing air up against gravity holding the weight down would provide a slightly more linear pressure reading. this way its always blowing against the full surface area rather than a diminishing surface.

Hi there, my suggestion is to balance your door/flap so that the T-30 just about maxes the gauge out... because no normal 120mm fan running on an AX12-25 is going to go that high. That should also bring the stock AX12-25 closer to the middle of the scale.

Great idea, even better execution!

Love it! Use a high vis protractor to get accurate angle of deflection and you'll be GOLDEN!

Man I've missed the fan showdown!

Would be awesome to start a contest on submitted Impeller blades for a 3D-printed water pump and test self-priming (height), psi, vertical lift, and GPM. Could still be PC-related if used for CPU cooling. EDIT: yes, using a static pressure test would be cool, and other tests. The water test mentioned might be a better test tho.

Fellow mechanical engineer here. Seeing lots of people suggest a U-tube manometer, but I'm not convinced that'd work very well for this application since the difference in pressure between the two sides of the fan is so low, not to mention any static pressure would likely be overshadowed by the venturi effect resulting in a device that essentially measures velocity anyway. The biggest problem with this machine at the moment is that it's not measuring static pressure at all -- it's measuring a quantity related to the stagnation pressure, which is a function of both static pressure and velocity (it's not quite the stagnation pressure since the air doesn't quite come to a complete stop when passing the flap). If you wanted to accurately measure static pressure you need to make the velocity of the air zero, i.e. have a fan blow into (or out of) a sealed container and measure the difference between the pressure within the container and atmospheric pressure somewhere far away from the fan. The only practical way I can think of for doing this with such low pressures is an actual manometer, unfortunately. That being said, I still think that this is an interesting way to gauge the effectiveness of a PC fan and could definitely be used in the next season, albeit with a change in what you claim the device is measuring. Several other people in the comments have left great ideas about how to improve the repeatability and resolution of the device so I won't repeat them all here.

You're so smart bro. Very inspirational. I love the if I can create it I will mind set. As well as the open sourcefulness. ❤

Hey man! Remember psi is per square inch! I think a better way would be to see how many grams of thrust is produced then dividing that by the square inch size of your push plate. This giving you thrust per square inch. Also don’t flip the flap, the flap should be pushed parallel to the thrust produced.

Can you use known values from certain fans to calibrate your scale?

I like this design. I think it's a very good way to compare fans

Interesting. These new tests make the show even more interesting.

Man, ur one innovative cookie! Keep it up bud!

I would strongly suggest to print at least 1 or 2 alternative flaps with more weight and probably also oversize the length by a good margin. The static pressure creates a force against your flap and you basically only measure that force by seeing how far it pushes your weight up. The current problem with this is that the greater the angle of the flap the lower the amount of air that actually reaches it and applies force. So you have a system that for e.g. linear gains in static pressure only measures sublinear changes. With your concept I don't see a solution how to circumvent this entirely but if your flap is longer it means that even at an angle the 'whole' air stream will still reach it. And if your flap has more weight the applied force will move it less, meaning your angles stay within a smaller interval and have less impact on the force balance. If you are interested in a different concept I would suggest to use a spring with a low spring constant and place that inside your tunnel with a flap that moves collinear with an increasing air stream instead of at a varying angle.

great idea! maybe some of the big brains here could argue my idea further but... use a potentiometer on the door axle and measure the resistance. with that you could dial in some insane mini increments. love the channel, great work!

I like your idea. I would love to see how the results look as the season goes on

E4 mafia to E4 Mafia. You can take this concept linear! Use some springs, and make it push the grid open from the flat side and the flat side only. Making it push the grid open on one side only completely delegitimizes your solution!

I love this contraption, and i think the most important thing to figure out would be a name for your unit of measurement :) My best suggestion would be "Fannies" because haha funny word :D

This is pretty cool. I see a bunch of comments talking about non linear measurements on it which make sense, but this scale can be logarithmic similar to Decibels. Neat concept. Curious to see how this plays out this season.

This works for the job. As a few have pointed out, making the arm at top a little longer while adjusting the weight value for the counter arm to get finer measurement. Kinda like adding a .1 to .9 to the scale for the deciding numbers. New fan designs and even some of the older fans that would show promise to test again can be in this group.

Like several comments have said, a u shaped of tube filled with water or other liquid i.e. alcohol, can buy used as a manometer, tilting the board the tube is mounted to will increase the resolution and you can use trigonometry to find the actual results, or just use it as is to compare fans without getting a perfect number

Im an aerospace engineer- i can say that this should do alright, but it’s technically still a dynamic pressure meter/ flow meter- flaps like this have actually been used on early aircraft to measure speed. It’s still a solid idea though.

I actually made wind tunnels to test samples in conditions at work. My dad is retired NASA and put me in contact with the head of the wind tunnels at his base. He made two very helpful suggestions to ensure I had laminar flow at my sample port. I needed to use streamliners in the tube. He suggested jumbo straws. Next I needed 6x the diameter in tunnel length from the streamliners to the sample port and at least 2x after it. It worked perfectly. I get nice even and non turbulent flow at my test port. In your case your test port is your flap. So add a tube after and lengthen you tube before and add straws equal in length to the diameter. I used 6" PVC for my tubing.

INCLINED TUBE MANOMETER!!!! Since you do not have a large static pressure differential to raise a "vertical" U-Tube manometer water column a measurable amount just make a longer run of tubing at a slope to give yourself a more granular accurate measurement.

I like the idea of building a test rig instead of spending a ton of money on meters. Some other comments made strong points about flaws in the current design. Good luck!

Woo Fan Showdown is back!

Interesting idea. If you split the flow straightener to leave a little gap in the middle and then 3D print an averaging ring duct around the sides with ports all around the edge. This can then be tapped and piped off to a simple inclined U-tube manometer to get very accurate static pressure measurements.

Pretty good Mk. I static pressure gauge. Can't wait to see the tests, and possibly a Mk. II when what improvements can be made become more apparent.

I think it's a cool idea! I think this and the wind tunnel measure different things, so I think both tests are useful info.

I think exploring in the direction of static pressure is a natural direction for this sweet experiment. I used a digital kitchen scale(4" x 4") with a plastic bag made into a tube tape sealed to it, sealed that to the bottom of a 120mm wind tunnel. Got repeatable results matching Noctua's P-Q graph. Another guy on reddit used a cork floating on a sealed water dish with an indicator off the side of that, got solid results too. Some pics on print-ables --> GPU/CPU Fan, the PSF (Psychedelic Super Funkitron )

This is better than an official set up because it comes with love

Mount a laser pointer to the flap so you can project it long distances and get a more precise reading. You could use a double mirror to extend the beam length in a tight space if needed. Just make sure it stays calibrated if you do that.

cool elegant result

I like the pressure machine. Great work!

Measure everything. Add your new rig, keep all the rest, too. I really like that you're still improving your benchmarks. I'm constantly surprised how compelling the fan showdown is to follow.

I like the idea of trying to shoot for your control being in the middle. Add a little bit of glue to the top to counterbalance it until your control is indicating in the middle. And I do also love the idea of having both results because yes your rig is nice but it's not a realistic thing of like a radiator. So people could see a realistic thing and then also comparable numbers in a scientific way with your device

Interesting concept to show an apples-to-apples comparison between fans. For the purposes of what you're doing, it's a really neat solution. For more precise measurements, you want to measure static pressure at zero airflow, so you'd need a sealed chamber and a manometer. Most PC fans are in the

A key thing to keep in mind is that the air pressure and air flow are related and not necessarily in a linear way. All of your tests so far, including this one, are testing some point on the pressure-flow curve using different resistances. The open tunnel was about as low of resistance as you could get, which is basically the maximum airflow - an interesting number, but not really reflective of a practical application. The radiator applied a considerable resistance, which makes it a much more practical working example. Measuring the airflow with the radiator tells us something about a point a long that pressure-flow curve, where the pressure determines the airflow through the resistance (the radiator). If we knew more about the radiator, we could calculate the total power of the fan as a combination of the pressure and flow developed. What you are aiming for now is pure static pressure with zero flow. In order to get that, you need it to actually be zero flow, so it has to be into some kind of closed orifice. The classic water tube is one way to measure the static pressure at the outlet. Perhaps you could direct that pressure into some other mechanism that would indicate the pressure, such as gauge using a diaphragm and spring. Which, at the end of the day, is just an analog pressure gauge. I looked at low pressure digital manometers for last season and the costs were prohibitive. Even more annoying is that lots of gauges will mention the resolution of their display, but not the minimum pressure or the accuracy of the measurement itself. I bought one that I thought could be useful and it just barely tipped the scale off of 0 when applying the full static pressure of a 50mm blower for a 3D printer nozzle, so that's useless. Models that seemed useful were at least a few hundred dollars, which might be worth it for running a KZfaq channel, but certainly wasn't worth it for me to play around with making my own fan blades and nozzles. However you manage to measure the static pressure, I think it's important to judge a fan just by a single characteristic. A fan that maximizes peak air flow at zero resistance will have terrible static pressure and vice versa. That's why airplanes use different motor and prop configurations depending on whether they are meant for level flight (airflow at high air speed) or 3D use (static pressure for hovering). That's why all those compressor designs did so poorly for maximum airflow in the wind tunnel test. Another consideration is that fans have a stall speed. If you apply too much resistance and the airflow through them decreases, the behaviour of the airflow over the wing changes and you get a completely different behaviour. Knowing the static pressure at zero flow and the max flow at zero static pressure tells us what the ends of the spectrum look like, but nothing in the middle. What I would love to see is an actual sweep of the pressure-flow curve. What kind of resistance can it handle? What use cases is this fan good for? Does it fall apart at the slightest resistance or can it handle a clogged radiator and still function decently? I think you'll find that the Noctua is good specifically because it maintains a solid flow even up to relatively high pressures. What about the wind tunnel but with a variable grid in the middle, like you might have in a floor vent (I forget the name of that grate design). By varying the cross-sectional area of that part of the tunnel, you control the vast majority of the resistance along the path, and therefore can see how pressure and flow vary with that resistance. Sweeping this through several points from fully open to fully closed should give you a good idea of that pressure-flow curve. Even if you can't measure the static pressure that builds up behind the grid, we know that, below the maximum air flow, the air flow is determined by the resistance of the grid and the pressure behind it, and the grid is the same for all fans tested, so the pressure is simply a function of that flow. Bonus points if the settings for the grid can be matched against common situations like a typical computer case and a radiator to give an idea of how that fan would work in those everyday situations. As for scoring them, it's not immediately obvious how to get a single number from this, but a common metric in similar situations is to take the area under the curve. By taking the area under the curve, we measure how well it works across all situations, rather than just one. With the same area, you could balance it to be really good at static pressure or really good at max airflow. But if you manage to improve both, that will show up as an increase in the area, making it an overall better fan.

I prefer your inhouse engineered testing solutions. I think it is what makes your channel so great! That being said, you do run into issues with airflow exiting the sides of the flap once you reach a certain point. Your data point grouping will be very very close. But a mechanical visual result is way more entertaining than numbers on a 200$ device.

To the Author, did you realise that the first airflow meters for fuel injection engines in the mid '80's used this 'trapdoor' arrangement? They were restrictive but accurate and I love you for using this method to upgrade your test results 😅 love your channel and will stay tuned to all your future posts😀

I like it. Simple, Repeatable. Easy to compare results. My only suggestion would be to increase the counterweight or change the flap size because the over-powered fan should be closer to 100% of your scale.

That’s such a great idea to measure pressure performance!

You could also construct a large baffle that goes around the apparatus that way no room air or just other air disturbances can affect the test can affect the test. It would pretty much be a loop and that way you could also potentially get rid of noise in the data. If you were to do this and add a monomer to it it would allow you to test different static pressures. In doing this you would basically make a fantastic machine that could reliably test for any static pressure

Perfect! It's like a speedometer! Love it! Just add a little bit more counter balance to it.

What a great contraption bro ! This is soooooo coool. I want to see a ton of fans tested ! Can you test some of the lian li fans and some more phanteks ?

Another thought is still using a smaller door for more resolution but require a minimum open angle while Adding some type of small weights to the door on the standard a12x25 to reduce to this minimum angle. This way you can judge each fan by the amount of weight required to open the door required distance. This will definitely restrict the outlet volume to the sane size on each fan while giving an idea of the fans ability to deal with static pressure. It wouldn’t matter if you even used paper clips as long as the increments are small enough to get good resolution in the weights. It’s the simplest way to go build this without extra complexity.

This looks awesome

I was thinking about using the definition of the static pressure itself: mm H2O My idea was a sealed chamber with a hole that a fan can be mounted onto it with a decent seal. another opening is pointed downward then curl back up like a U that is filled with water. The pressure will be measured by the difference in height between the 2 half of the U pipe.

At work, we use Dwyer 477AV manometers for low pressure gas measurements, but they are a bit pricey at ranges of 20" w.c. or less (which you probably want the 4" or maybe even 1" models for the highest level of accuracy). I have found Superior Sensor Technology has some low pressure sensors which can communicate either I2C or SPI with good accuracy specifications. They even have some evaluation kits that you can use to hook up via USB to a PC for taking measurements (such as EK04-HV-SPI or EK04-HV-I2C). I wouldn't recommend using an actual water column manometer, because getting a good one that is in the 0"-1" w.c. range can be quite expensive and you have to periodically fill those back up with special fluids.

I think that if you (mostly) close the sides of the door, even with a transparent panel or something like that, the increase of the area where the air can escape would be slower when the panel opens and you might be able to get more granular results than you're getting now where I fear the fans might end up all too clustered on similar value. Closing the bottom too might help if the sides are not enough.

Maybe a sealed box with a small water resivor and a clear hose going straight up. Right now its a simi static pressure test. As the door opens the pressure will drop and the fan can then speed up and then it's not really a static pressure test. Keep up the great work man 😊

The design is excellent. The only thing I'd change is extend the walls a few cm after the flap, so it actually pushes back more on the mass of the air, instead of just hanging in there once a sufficient gap is created to allow for all the air to flow out fast.