Water cooling and negative air pressure?

0d3nnis0

0d3nnis0

0d3nnis0

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13 Jan 2020
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Hi there,

i am new to this forum and i hope this hasn´t been discussed a hundred times. I am not a native english speaker so please excuse my wording.

I´m wondering if someone has experience with full negative air pressure in a water colled system by using only exhaust fans and no input fans. It really bothers me to buy the newest RGB Fans for 30$ just to mount them upside down and stare at cheap sticker on the back while all this RGB-goodnes lightens the inside of my radiator... I found some tests stating negative pressure is better for overall temps. There is even a test by Linus showing that there is less dust entering the case than in a neutral pressure environment. But all these tests refer to air colled systems as far as i can see, so i wanted to ask if somebody gave it a try or even runs a system like that and would like to share their experience?

For those of you who are interessted, i am running a LianLi O11d with one 360 radiator on the bottom and one in the top so temperatures are no problem its all about the look

.....with all that ARGB-madness going on i wonder why nobody offers fans in Pull-configuration.

cheers
Dennis
 
Hey doyll,

thanks for your reply. I have a LianLi o11d with two 360 rads, one at the bottom and one in the top. Currently running with 6 LianLi BR lite but I gonna change them for Corsair ml120 pro rgb.
I am pretty familiar with airflow setups but like I said I really wanna try negativ for the aesthetic. I think I just have to give it a try, temps should be good and adiditonal dust filters at the back/pci slots should help ceeping the case clean.

Cheers

kj76g2L.jpg
 
Yeah i know but you still see the spider at the back which bothers me and the ml120 just seem to be the better performer. And for the lack of brightness i just install two aditional RGB stripes...
 
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Why do you want to have a negative pressure case?

We talk positive pressure and negative pressure like there is much difference, but the reality is the amount of pressure computer fans make is minisqule .. about as much difference in pressure as there is between air pressure at sea level and at about 10 feet above sea level .. only enough to move air.

10 feet of elevation change at sea levle at 15c is 3.727mm H2O of pressure change. ;)

Altitude to Pressure Conversion
Altitude Change
ft . . . m . . . ps . . . . . mm H2O . . . . . mm H2O
0 . . . 0 . .. . 14.696 . . 10332.276 . . . . 00.000
1 . . 0.3048 . 14.69546 10331.9308651 . 00.34514
10. . 3.048 .. 14,6906 . 10330.41348 . .. 03.72706
50 . 15.240 .. 14.669 .. 10313.650713 .. 18.6353
100. 30.480 . 14.643 .. 10295.025426 . . 37.250
 
I think you got me wrong. It is not like i musst have negative pressure, I just want all my fans "facing up" (exhaust) for the aesthetic which results in negative pressure. So I am looking for the pros and cons especially regarding that all tests I found so far are claiming its best for temperatures overall. Nonethless nearly everybody goes for neutral/positive pressure and I wonder why...
 
I don't think it really makes much difference whether positive or negative pressure, just as long as the airflow is good. In your current setup you have 3 intake and 3 exhaust, so the amount of air coming in roughly equates to the amount of air going out.
If you have all 6 fans as exhaust then you need to ensure that plenty of cool air is entering the case from elsewhere, like the PCI slots. Adding extra dust filters to the PCI slots will only make the airflow situation worse.
 
To be honest
In your case I doubt positive /negative will make much difference you have a good custom loop
A few degrees maybe
The main thing is actually having air flow
I would do it how its aesthetically pleasing to you
I seriously doubt you will have any thermal issues
Some people worry too much over a few degrees C
If temps are at a decent level then why worry that turning all the fans around might be 3c cooler or whatever
You can always try both if just curious
Since every one's setup is different we can't guess the exact effect it would have for you anyway

And if all fans are exhausting air then of course air is coming in somewhere
Your fans can't pump all the air out leaving a vacuum
 
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Negative vs positive pressure case makes no difference in performance as long as pressure differential is the same for both .. and the amount of pressure differential our fans make is so little it doesn't take much resistance to stop air from flowing.

but if we need equal vent airflow potential of vents bring air into case as we have vents letting air out .. it's simple physics that our cases cannot flow more air then the lesser potential amount of intake vs exhaust. Think of airflow as water flowing . On a practical level if we have a case with 6x vents all the same size with same grilss we need 3 flowing air in and 3 flowing air out. If we have 4 flowing air in then the 2 flowing air out we limit the amount of air flowing to the amount the 2 vents are flowing out.
 
@Mcnumpty2323 thanks for your thoughts. I am pretty sure I will go with the all exhaust attempt and forget about it when temps are pleasing. Unfortunately there isn´t much space underneath the graphics card so flipping fans is a pain in the ass, time will tell if i am curios enough to compare temps :D

doyll said:
Negative vs positive pressure case makes no difference in performance as long as pressure differential is the same for both
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there is a difference, one can argue how much but there is.

doyll said:
If we have 4 flowing air in then the 2 flowing air out we limit the amount of air flowing to the amount the 2 vents are flowing out
Click to expand...
that would only be true for a completly sealed case. In those "open" cases we are dealing with it is nearly impossible to create neutral pressure environment where air volume coming in (through fans) equals the air volume going out (through fans), but that´s beside my point...
 
0d3nnis0 said:
@Mcnumpty2323 thanks for your thoughts. I am pretty sure I will go with the all exhaust attempt and forget about it when temps are pleasing. Unfortunately there isn´t much space underneath the graphics card so flipping fans is a pain in the ass, time will tell if i am curios enough to compare temps :D

there is a difference, one can argue how much but there is.

that would only be true for a completly sealed case. In those "open" cases we are dealing with it is nearly impossible to create neutral pressure environment where air volume coming in (through fans) equals the air volume going out (through fans), but that´s beside my point...
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Can you give me any data that shows any difference in component temps bases solely on fans pulling air out (negative pressure case) vs fans pushing air in (positive presure case)? Keeping in mind the air temp into coolers needs to be the same. Because different placement of fans (as well as fan speed) created different airflow paths that almost always result in differing air temp to components .. but that's not the same thing as neg vs pos pressure. I'm guessing , are you really talking about airflow and it's paths and not really neg vs pos pressure? ;)
 
doyll said:
Can you give me any data that shows any difference in component temps bases solely on fans pulling air out (negative pressure case) vs fans pushing air in (positive presure case)
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sure https://www.youtube.com/watch?v=srhw_mPZkj4&t=271s
https://www.hardwaremax.net/guides/hardware/305-der-perfekte-airflow?showall=1&limitstart=
the basic idea is, that an intake radiator would "feed" warm air to all the components within the case including the exhaust radiator, so only one of the rads gets cool ambient air... makes sense in my opinion.
If you break it down to just one radiator like an AIO setup, pretty much everyone would suggest to mount at exhaust at the top and not as intake in the front!?
I don´t want to offend anybody, I´m just seriously curious. Some times people do things because it´s done that way for ever but what´s proofen for aircooling doesn´t need to be best for watercooling. I hope you get my point here..

Cheers
Dennis
 
Seems reasonable, but it's more the result of changing airflow paths, not negative vs positive pressure that is giving lower air temp. I often use a themometer with remote sensor to monitor air temp different places inside of case and change that temp by fan placement and rpm. 2nd post above has link with image of what I use. Sometimes slower speeds give lower temps, sometimes higher speeds.
 
drakulton said:
I don't think it really makes much difference whether positive or negative pressure, just as long as the airflow is good. In your current setup you have 3 intake and 3 exhaust, so the amount of air coming in roughly equates to the amount of air going out.
If you have all 6 fans as exhaust then you need to ensure that plenty of cool air is entering the case from elsewhere, like the PCI slots. Adding extra dust filters to the PCI slots will only make the airflow situation worse.
Click to expand...
Agree. Having the same number of fans as pushing air in as exhaust, even if the exhaust (when not dealing with the extra barrier of a filter to overcome), will more or less balance out.
If it was all pushing air in, the airflow as exhaust would need to find a space to exit the case. Tried here before and somehow the hot/warm air was mostly trapped at the GPU area. Using a big case, Enthoo Primo.
Using all fans as exhaust, the air required to be exhausted, would need to come from somewhere, and quite frequently, it will find its way through unfiltered gaps.
The best way is balanced, but as you're more worried about the looks of it, either get few of those RGB rings.
Another solution would be to have it as exhaust, as you want, but sort some fans pushing air in at the front of the cas, if possible.
 
You could go really mad and add extra air intake capabilities to the case. Depending on which orientation you have your PSU, remove it's cover (not the PSU shroud ) and flip the PSU fan so it's now sucking air in from the back . Refit the PSU with the fan blowing up into the case not down out of the bottom of the case.
 
More fans may or may not help. It's not so much about number of fans or how much air we can push into/through a case, but more about what paths that airflow is taking and how well heated exhaust airflow is flowing out of case versus mixing with cool intake air going to coolers. With air cooling component temp rises almost 1:1 ratio to airtemp at same fan speeds. So is air temp is 10c higher than room, component temps will also be 10c hotter.
 
MrPotato said:
...some fans pushing air in at the front of the cas, if possible
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The 011d doesn´t has any front mount possibilities and with my setup I "only" have 3 fan spots in the bottom and 3 in the top left.
drakulton said:
You could go really mad and add extra air intake capabilities to the case. Depending on which orientation you have your PSU, remove it's cover (not the PSU shroud ) and flip the PSU fan so it's now sucking air in from the back . Refit the PSU with the fan blowing up into the case not down out of the bottom of the case.
Click to expand...
Interessting idea, but the PSU is located in a back chamber so that´s not an option.

I just gonna try it with all fans exhaust when my ml120 arrive....
 
The only downside of negative pressure is that dust is meant to be sucked into the case whereas positive pressure is meant to blow dust out of the case (well reduce it settling in there). I don't find any difference. And it seems irrelevant if you have dust filters on the front (apart from the fine dust that goes through the mesh). I have seen youtube videos of jayz2cents and gamersnexus where they have done stupid things with case fans (like having all the fans blowing into the case!) and ultimately there hasn't been much difference).

I assume that you will clean your case out every 3 months to a year?
 
Alan1969 said:
I assume that you will clean your case out every 3 months to a year?
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Yes, since this case has two glas panel I clean it very frequently.

I just gonna observe it for 2-3 month and if dust is getting a problem I instal aditional dust filter. Interestingly there is a video by Linus where he compared possitive, neutral and negativ airpressure over one year in terms of dust and the negativ system collected the least :eek:
 
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