Is Neg air pressure really that bad?

[Xdrone]

I will have three intake and three exhaust fans in my build.

The exhaust fans run at higher rpm.

The case is off the ground, less dust.

Are there any problems with this, mainly regarding negative air pressure?

[sazrocks]

We'll find out in a few months.

 

[vanished]

In theory yes, since it will cause air to be drawn in through every little gap in the case to make up for the deficit, where as with "positive pressure", air will be flowing out through these holes, meaning the only air that enters through the case is drawn in by the fans you dedicated to doing it, which are pulling through a filter (if you set it up properly).

 

7 minutes ago, sazrocks said:

We'll find out in a few months.

 

I have to wonder how this might have been impacted by the construction work...

[smartroad]

2 minutes ago, Ryan_Vickers said:

In theory yes, since it will cause air to be drawn in through every little gap in the case to make up for the deficit, where as with "positive pressure", air will be flowing out through these holes, meaning the only air that enters through the case is drawn in by the fans you dedicated to doing it, which are pulling through a filter (if you set it up properly).

Thats what I understood as well. My machine sits on the floor so I have designed it to pump more air into the case then out under low/medium loads. It is only if the CPU/GPU get mega hot that my design may move into a little negative pressure. Which reminds me, must clean filters...

[vanished]

This is probably a good time to explain what's really going on, in case anyone cares or doesn't know.

 

When you first power on the fans, the ones pointed in start pushing air in and the ones pointing out start moving it out.  Depending on the net flowrate of air (if there is more going in or more going out), air will either start to build up inside the case (we call this positive pressure) or it will start to suck the case down, like a vacuum (we call this negative pressure).  Because cases are not very well sealed, and case fans are not very powerful (yes, even your fancy static pressure optimized ones) this process quickly "plateaus", or reaches what we call "steady state".  At this point, the pressure in the case is either above (positive) or below (negative) that of the room it's in, and because of this, certain fans get more or less effective, and air starts to move in or out of other cracks in the case where no fan exists.  At this point, air is moving in as quickly as it is moving out, and it will remain this way unless fan speed is changed again to disturb the system.

[PeachyUwUSenpai]

no not really worrying about airflow is what people do after their done min maxing everything else it's like trying to decide between noctua thermal paste and artic silver aka less than a 1% difference in anything real world

[LogicalDrm]

Simplest terms. Negative performs better, but brings in more dust from all holes which aren't filtered. Positive brings less dust but doesn't cool that well. Neutral would be best but is really hard to achieve.

[vanished]

8 hours ago, LoGiCalDrm said:

Simplest terms. Negative performs better, but brings in more dust from all holes which aren't filtered. Positive brings less dust but doesn't cool that well. Neutral would be best but is really hard to achieve.

Please explain how negative vs positive vs neutral would have any inherent effect on cooling ability...

[airdeano]

simple and relatable terms

you eat 2 pounds of cookies and crap 2 pounds you have a neutral position= good (in with the good, out with the bad)

you eat 2 pounds of cookies and crap 1 pound you have a positive position = bad (still got 1-pound of cookies left taking up space)

you eat 2 pounds of cookies and crap 3 pounds you have a negative position= worse (s'mthing other than cookies has fallin' out - see a doctor immediately)

[LogicalDrm]

1 hour ago, Ryan_Vickers said:

Please explain how negative vs positive vs neutral would have any inherent effect on cooling ability...

Not any direct. But try to explain it to half of people in here (same who still think hot air rising has any effect). So being as simple as I can, more exhaust = negative = more hot air removed = better cooling performance.

[vanished]

11 minutes ago, LoGiCalDrm said:

Not any direct. But try to explain it to half of people in here (same who still think hot air rising has any effect). So being as simple as I can, more exhaust = negative = more hot air removed = better cooling performance.

Except that regardless of positive or negative, once it's been running for a few seconds and reaches steady state, the rate of air in is the same as the rate out (obviously, or the case would eventually implode/explode).  Neither one inherently causes more or less exhaust, they just dictate where that exhaust leaves the case, whether it's through the fans pulling it out (negative), or through any gap it can (positive).

[LogicalDrm]

13 minutes ago, Ryan_Vickers said:

Except that regardless of positive or negative, once it's been running for a few seconds and reaches steady state, the rate of air in is the same as the rate out (obviously, or the case would eventually implode/explode).  Neither one inherently causes more or less exhaust, they just dictate where that exhaust leaves the case, whether it's through the fans pulling it out (negative), or through any gap it can (positive).

So essentially it's all about dust. Which only matters if one lives near heavy industrial area or next to dessert.

[vanished]

Just now, LoGiCalDrm said:

So essentially it's all about dust. Which only matters if one lives near heavy industrial area or next to dessert.

Well, there's dust everywhere, even in a relatively clean house, but yes, that's the idea.  You can have good or bad airflow with positive or negative - that's not why people pick one or the other.  The difference is just about dust control, since with positive pressure you can ensure that the only air entering the case enters through your intake fans and thus if you put a filter on them, you'll have clean air inside, whereas with negative pressure, air will be sucked in through every little gap to feed your exhaust fans and with it, they will bring dust.

[HisEvilness]

Negative: Best Cooling results but more DUST is attracted.
Positive: Cooling is slightly hampered with poor cable management dead air pockets can decrease your cooling efficiency.
Balanced: Keeps out the dust as well as being efficient in cooling over positive pressure.

Made this sheet when I wrote my article to test out various pressure setups: Case Cooling CFM, Static Pressure and Watt Calculator (1).ods

[MrMarriarty]

Been pointed here from another thread..... so are we all in agreement from a cooling point of view negative is best? im happy to argue the science with any non belivers lol

[HisEvilness]

2 minutes ago, MrMarriarty said:

Been pointed here from another thread..... so are we all in agreement from a cooling point of view negative is best? im happy to argue the science with any non belivers lol

I would just buy fans in the name of science and change cooling solution once per let´s say 3 months, it all does the same but as with intel and AMD people have a preference.
Negative pressure is what I am running since it offers the best results for me.

[vanished]

1 hour ago, MrMarriarty said:

Been pointed here from another thread..... so are we all in agreement from a cooling point of view negative is best? im happy to argue the science with any non belivers lol

No, we're not because it's absurd and nothing you can possibly bring up will support it.  I've already explained here how it works, and the reason(s) one might choose one setup over another.

[MrMarriarty]

9 hours ago, Ryan_Vickers said:

No, we're not because it's absurd and nothing you can possibly bring up will support it.  I've already explained here how it works, and the reason(s) one might choose one setup over another.

Science time....
So today we are going to be learning about thermodynamics, in particular conduction and radiation of heat.

 

Conduction (Your heat sink) (EDIT Technically convection has a part to play as well within the heat pipes)
When heat is transferred via conduction, heat is transferred internally, by vibrations of atoms and molecules.Metals have many free electrons, which move around randomly; these can transfer heat from one part of the metal to another.

 

Radiation (From your heat sink to the air in your case)
Energy is transferred in the form of electromagnetic waves. When everything is at the same temperature, the amount of energy received is equal to the amount given off. Because there is no net change in energy, no temperature changes occur. When things are at different temperatures, however, the hotter objects give off more energy in the form of radiation than they take in; the reverse is true for the colder objects. The amount of energy an object radiates depends strongly on temperature.

 

We can use the following equation to express this... the important part here is the “triangle” next to the "T" in the top  right. It represents difference in temperature

 

So how does this apply to pc cases and cooling you say? Well positive air pressure (pumping in more cool air than your exhausting hot air) will cause the ambient temperature in your case to rise*, which in turn will slow down the transfer of heat from the heat sink to the air around it. Purely because the electrons in the air have more energy so they absorb less. Negative air pressure (exhaust your hot air faster than your putting cool air in) keeps the temperature gradient within your case higher, thus promoting faster heat transfer to the air. If you were actively cooling the incoming air say with AC then this makes the effect less prominent but still a fact

 

Now we are only talking about a few degrees difference depending on your components but isnt that what pc coolings all about a degree here and a degree there? Yes bad air flow will have a greater impact on cooling with dead spots, hot spots ect. But we are talking about the transfer of heat not air flow that's another lesson altogether as are AIO’s as we need to start looking at convection of fluids for this
 

*By keeping the heat in your case longer the hot air will transfer heat to the cool air

[Cyracus]

20 minutes ago, MrMarriarty said:

Yes bad air flow will have a greater impact on cooling with dead spots, hot spots ect.

I seem to remember Luke doing a workshop video where he filled the pc case with a bunch of junk to obstruct airflow and there was no change in operating temperature, if there was it was like 1ºC 

But I remember seeing someone test airflow, ridiculous negative and positive and a somewhat balanced setup, negative did slightly better and the balanced setup with sensible airflow was the best. I'd try to find it but google is my bitter enemy and refuses to give me the search results I desire... @#*%ing google

[MrMarriarty]

4 minutes ago, Cyracus said:

I seem to remember Luke doing a workshop video where he filled the pc case with a bunch of junk to obstruct airflow and there was no change in operating temperature, if there was it was like 1ºC 

But I remember seeing someone test airflow, ridiculous negative and positive and a somewhat balanced setup, negative did slightly better and the balanced setup with sensible airflow was the best. I'd try to find it but google is my bitter enemy and refuses to give me the search results I desire... @#*%ing google

Air flow is much more complicated as it really depends where the turbulence is to how detrimental it is, my fluid dynamics is a bit rustier but i can have a pop at explaining that if you want

[Cyracus]

5 minutes ago, MrMarriarty said:

Air flow is much more complicated as it really depends where the turbulence is to how detrimental it is, my fluid dynamics is a bit rustier but i can have a pop at explaining that if you want

That's alright, I have a pretty good understanding of all that, just figured I'd keep it short and skip the technicals

[vanished]

1 hour ago, MrMarriarty said:

[...] So how does this apply to pc cases and cooling you say? Well positive air pressure (pumping in more cool air than your exhausting hot air) [...]

We need to address this first before we have any hope of exploring more complicated aspects of this scenario.  As I have said many times before, regardless of how your fans are configured, once the pressure inside your case stabilizes at higher or lower (or even equal to if you can manage it) than the outside room air, the rate of cool airflow into the case equals the rate of hot airflow out of the case.  If it didn't, the case would continue to fill up, or get sucked down, until it exploded/imploded.

 

If you can't agree with that then frankly there's no hope of continuing this discussion of delving into anything more complicated.

 

But I'll go on just for the sake of it.

1 hour ago, MrMarriarty said:

Conduction (Your heat sink) (EDIT Technically convection has a part to play as well within the heat pipes)
When heat is transferred via conduction, heat is transferred internally, by vibrations of atoms and molecules.Metals have many free electrons, which move around randomly; these can transfer heat from one part of the metal to another.

Yes, and while the effect is likely too small to even measure, in all likelihood, the rate of heat transfer from the heatsink to the air that's cooling it is higher in a positive pressure scenario due to the air being of a higher density, but I wasn't even going to bring it up since, like I said, the effect is so small I doubt anyone could reliably measure it with ordinary tools.

1 hour ago, MrMarriarty said:

Radiation (From your heat sink to the air in your case)
Energy is transferred in the form of electromagnetic waves. When everything is at the same temperature, the amount of energy received is equal to the amount given off. Because there is no net change in energy, no temperature changes occur. When things are at different temperatures, however, the hotter objects give off more energy in the form of radiation than they take in; the reverse is true for the colder objects. The amount of energy an object radiates depends strongly on temperature.

 

We can use the following equation to express this... the important part here is the “triangle” next to the "T" in the top  right. It represents difference in temperature

Yes, but regardless of your setup that plays virtually no role here since positive vs negative isn't going to alter the temperature of your components, heatsinks, or the case itself in any meaningful way, as already stated.

1 hour ago, MrMarriarty said:

So how does this apply to pc cases and cooling you say? Well positive air pressure (pumping in more cool air than your exhausting hot air) will cause the ambient temperature in your case to rise*, which in turn will slow down the transfer of heat from the heat sink to the air around it. Purely because the electrons in the air have more energy so they absorb less. Negative air pressure (exhaust your hot air faster than your putting cool air in) keeps the temperature gradient within your case higher, thus promoting faster heat transfer to the air. If you were actively cooling the incoming air say with AC then this makes the effect less prominent but still a fact

*By keeping the heat in your case longer the hot air will transfer heat to the cool air

Already went over this, the whole sentence and the rest of the paragraph is made useless by the fact that what I bolded is simply absurd and incorrect.

 

You're right that if the temperature in your case goes up that the components will also heat up, since all component temperatures are maintained at some offset relative to ambient, where ambient in this case is technically the internal case temperature (though many make the simplification that it's relative to room temp), but having negative vs positive vs neutral pressure will have zero inherent impact on your case temp.  If you do see a difference going from positive to negative by moving fans and keeping all else equal, I promise you it's because air just happens to flow better with one fan configuration than the other (which is a whole other topic), and obviously increasing the airflow through your case (regardless of whether you maintain the inside at positive or negative pressure) will increase cooling performance.

[MrMarriarty]

10 minutes ago, Ryan_Vickers said:

We need to address this first before we have any hope of exploring more complicated aspects of this scenario.  As I have said many times before, regardless of how your fans are configured, once the pressure inside your case stabilizes at higher or lower (or even equal to if you can manage it) than the outside room air, the rate of cool airflow into the case equals the rate of hot airflow out of the case.  If it didn't, the case would continue to fill up, or get sucked down, until it exploded/imploded.

 

If you can't agree with that then frankly there's no hope of continuing this discussion of delving into anything more complicated.

 

But I'll go on just for the sake of it.

Yes, and while the effect is likely too small to even measure, in all likelihood, the rate of heat transfer from the heatsink to the air that's cooling it is higher in a positive pressure scenario due to the air being of a higher density, but I wasn't even going to bring it up since, like I said, the effect is so small I doubt anyone could reliably measure it with ordinary tools.

Yes, but regardless of your setup that plays virtually no role here since positive vs negative isn't going to alter the temperature of your components, heatsinks, or the case itself in any meaningful way, as already stated.

Already went over this, the whole sentence and the rest of the paragraph is made useless by the fact that what I bolded is simply absurd and incorrect.

 

You're right that if the temperature in your case goes up that the components will also heat up, since all component temperatures are maintained at some offset relative to ambient, where ambient in this case is technically the internal case temperature (though many make the simplification that it's relative to room temp), but having negative vs positive vs neutral pressure will have zero inherent impact on your case temp.  If you do see a difference going from positive to negative by moving fans and keeping all else equal, I promise you it's because air just happens to flow better with one fan configuration than the other (which is a whole other topic), and obviously increasing the airflow through your case (regardless of whether you maintain the inside at positive or negative pressure) will increase cooling performance.

I see why i was pointed here now, we need to grab a coffee and discuss this further! I understand and appreciate what you're saying but at the same time you must see that removing the hot air quicker is only going to improve the gradient between components and the air. Pumping in more cold is only going to "dilute" the hot air not directly address it... 

[vanished]

6 minutes ago, MrMarriarty said:

I see why i was pointed here now, we need to grab a coffee and discuss this further! I understand and appreciate what you're saying but at the same time you must see that removing the hot air quicker is only going to improve the gradient between components and the air. Pumping in more cold is only going to "dilute" the hot air not directly address it... 

Lets take a step back and really get the movement nailed down.

 

In any system, you can describe the flow like this:

 

Input - Out + Generation - Consumption = Accumulation

 

Now, we're not generating or consuming any air, so right away this simplifies:

 

Input - Output = Accumulation

 

Imagine a system with 4 intake fans and 1 exhaust.  When you first turn it on, Input will be higher than output and so Accumulation will happen like this (in a very generalized sense):

 

4 - 1 = 3

 

This is what establishes the positive pressure in the case.  You can easily imagine the same scenario for 4 exhausts and 1 intake:

 

1 - 4 = -3

 

This would establish a negative pressure system.

 

Regardless though, this can't carry on forever.  If it did, the positive pressure system would explode due to having more and more air shoved in, while the negative pressure system would eventually implode due to having every last molecule sucked out.  What happens rather quickly is once the case has positive pressure, it starts flowing out through all the cracks and gaps, and in addition to that, the exhaust fan becomes a little more effective, and the intake fans become a little less effective, and the system thus reaches what's called "steady state" where the rate of air moving in = the rate of air moving out:

 

2 - 2 = 0

 

This same thing happens with the negative pressure system, except all the little gaps draw air in, and it's the exhaust that gets less effective while the intakes get more effective.

 

The point is the rate of airflow through the case is one value - there isn't more going in or more going out, and it doesn't matter if it's positive or negative.

 

So for this reason the concept of "removing the hot air quicker" is simply nonsensical - in either system, you are just moving air through.  For every molecule in there must be a molecule out (well, not that precisely but on the large scale ).

 

If you're wondering about the temperatures of those streams, it's safe to say that the air going in is at the temperature of the room, and the air coming out (if we can assume well-mixed conditions within the case) is at the bulk temperature of the case air.  This is now the only variable of interest.  Obviously to maximize the rate at which heat is moved from heatsinks to the case air (so it can later be exhausted) you want the case air to remain as cool as possible.  This can be done in two ways - either cool off the room so cooler air is drawn in, and/or increase the rate of airflow through the case, thus bringing the bulk temperature down closer to outside ambient.

 

I think this is what you're getting at, but notice that there is no dependence on the pressure in the case, or what fan setup you have.  It's just a function of inlet air temperature and total flow rate.  You can't manually specify a separate rate for the inlet and the outlet because of the mass balance I explained earlier, and you can't selectively exhaust only the hottest air either unless you build vents from the outlet of your various components directly to the outside of the case, but in that situation the problem's been changed entirely anyway so none of this would be relevant.

[Xdrone]

3 hours ago, Cyracus said:

 

 

1 hour ago, Ryan_Vickers said:

 

 

1 hour ago, MrMarriarty said:

 

 

 

13 hours ago, HisEvilness said:

 

Alright everyone needs to calm down ? 

I appreciate the solid discussions, but I have come to a conclusion after analysing all this information I have received, I will keep it balanced, and get 6 ml120 fans all of which cover the intake and outtake (3 each).

Thankyou guys for helping me reach this conclusion.