I like speed adjusted but powerful computer fans exchanging outside air for inside air, and utilize both intake and exhaust fans, and with reflectix on the sunny side windows can keep my van's interior cooler than until about noon, then same as ambient temps, and by late afternoon when things start cooling off is the only time it is warmer in the van than outside it, and not for long.
I have not done so yet, but I will be replacing my one silverstone FM121 exhaust fan on my ceiling mushroom exhaust vent with a Noctua Industrial 3000 rpm 120mm fan.
The Noctua can move the same overall CFM as the silverstone(with no restriction/resistance), but for 25% less energy consumed, and has more than 2 times the static pressure rating. As my exhaust fans blow into a mushroom vent through a 4.75 to 4.0 inch stepdown ring, there is considerable restriction, so the higher static pressure rating should prove very beneficial to overall airflow and perhaps allow the same or higher airflow for signifiantly less noise and amperage consumed. Perhaps.
While the silverstone fm121 fan comes with a speed controller, the Noctua does not. But I have seen that Noctua is offering a speed controller that will control the speed of their PWM fan versions via the fourth PWM wire.
https://www.amazon.com/Noctua-NA-FC...r=1-12&keywords=computer+fan+speed+controller
https://www.amazon.com/Focused-NF-F...id=1499709718&sr=1-1&keywords=Noctua+3000+pwm
While I do not really require better ventilation, I am just so impressed with Noctua fan's engineering that I must obtain one of these high rpm industrial versions, and perhaps use less juice to move more air for less noise.
While I have the rain vents on my front windows, they are more for extra shade than ventilation. When I want to keep the interior cooler I have tight fitting reflectix shades stuffed into these windows which would allow very little air to be pushed past them by my intake fans located in a sliding conversion van window in back.
Also, while the 120MM computer fan has the most product choices, a bigger fan can move more air for less noise and sometimes less amperage consumed.
The 180MM silverstone fm181 fan can move ~150CFM for 0.28 amps, and is very quiet, and comes with speed control. My intake fans reside by my head in bed and i can sleep with the fm181 on full speed inches from my head, and love the airflow. My intake shroud has room for 3 fans, one 180 and two 120mms and fits tightly so any air moved by the fans cannot to a 180 and recycle through the blades. A fan shroud for 100% air displacement is so much mroe effective than just a fan placed in an open window.
Usually the 120MM ones in my shroud are rarely turned on. it has to be HOT to require them, and 120MM at higher rpms are not quiet, but the fm121s at minimum speed are.
Speed control of the fans, is very necessary, in my opinion.
Controlling PWM fans via the fourth wire is something I will be working on soon. I have one extremely powerful 120mm Delta fan that needs to be tamed as the airflow and noise are too much 99.5% of the time, but I would love that 252cfm that 0.5% of the time.
The 4th PWM wire needs a PWM signal sent at 5 volts.
While all fans can be speed controlled by using a PWM motor speed controller, or LED light dimmer on the red and black power wires, this is not a good idea on 4 wire PWM fans, and a lot of fans when slowed via the power wires will make a whining sound at reduced speeds, and the PWM signal might be bad for The motor itself. Those exploring this route should find pwm motor speed controllers with 21Khz or higher as only Fido should be able to notice the whining. Most are in the 11 to 15khz range, so do your research and find one which claims 21Khz or higher. I know of one person using a PWM motor speed controller on the industrial Noctuas and claims they do not hum nor seem badly affected by the 15KHZ PWm signal he feeds them on their powerwires, but the damage would eb cumulative, and they are located where any additional noise would not be a concern.
Many fan speed controllers also do so by controlling the voltage fed to the fan via a voltage buck converter.
These buck converters will require some overhead though, meaning if they are fed 12.8vDC the highest voltage they might allow on the output is 11.8v, and thus the max fan speed is not realized, which I find unacceptable, where as a PWM fan fed a PWM signal on the fourth wire should have the full speed range available, and perhaps suffer less conversion losses, meaning mroe efficeint.
When I have some acquired the components to cobble together to feed the fourth wire a 5volt PWM signal, successful or not, I will update on one of the other ventilation thread in which I have already posted a lot of info.
Those not into the DIY of electrics concerning fan speed control should likely consider the silverstone fans which come with a built in Speed control like the FM121 or fm181 or the fm92, which should mate nicely with some 4 inch marine vents for those exploring holes in the floor.
The noctua Industrial versions are just so well engineered though, that hacking their 21$ speed controller, to mimick a computer mother board, should be quite easy to accomplish for about 45$ with fan and speed controller. Not an inconsiderable sum, unless one is a ventilation Nazi.
The Noctua industrial versions also have some higher ingress protection ratings, meaning they are more resilient in dusty or moist atmospheres. Most all my fan failures have been from salt air laden moisture issues rotting the circuit board. My silverstone fm181 fan had its windings and circuit board coated with DEoxit shield spray, and the wires, where they are soldered to the circuit board, I covered this problem area with either 'amazing goop' or dielectric silicone grease, can't remember.
So far so good, but even if the FM181 fails tomorrow, I'd get another as it is so effective, and quiet
Silverstone offers a AP182 180mm fan which is much more powerful, and expensive, but I found it does not like battery charging voltages at max speed. The hub would get stinky plastic hot. this might have been a contributing cause to its failure, but green corrosion on the wires where they are soldered to circuit board was its the death knell.
My complaint with the silverstone fm 121/181 fans is their white color. I prefer black as it make it much harder to notice them in my conversion van sliding window, which only ever gets fully closed in winter. It is screened and security protected with fine mesh chicken wire. I have removed the impellers and spray painted these fans black, though one can easily throw off the balance of the impellers if not careful. A black sharpie works OK, but takes forever and comes off during fan blade cleaning.
Computer fans vary so widely in air moved for amps consumed and noise made than anybody who just slaps just any fan in place will not realize the full benefit available from computer fans.
Look at the engineering which goes into some Noctua fans.
http://noctua.at/en/products/fan
Their latest offering in the 120mm range is not yet available on Amazon or Newegg, nor it it designed to be a powerful fan, but its efficacy when attached to a computer heatsink is impressive.
I have a Noctua NF-f12 on the condenser of my compressor fridge pushing air through it instead of the original fan location which pulled air, and was rather stunned at the reduction of compressor run times. The Noctua fan draws 70% less juice, makes half the noise, and decreased the time which the refrigerator ran from about 5.5 minutes to just over 4.5 minutes each time it cyucled on, during my tests.
Their newest fan:
http://noctua.at/en/products/fan/nf-a12x15-pwm
apparently performs even better when attached to airflow restrictive finned heatsink, but draws 0.12 amps instead of the NF-F12's 0.05 amps. As the new fan is 10mm thinner, it might also allow even less restriction in my fridge cabinet. I've no problems with 0.07 more amp consumption and can retask the NF-f12 to exhaust my electrical cabinet getting rid of a loud ineffiecient 80MM fan I pulled from a failed Wfco converter.
