When in doubt: make it exhaust

[Bdonedge]

I have recently purchased a custom die panel with an additional fan which was supposed to be used for my video cards to make them cooler.
It's a 140mm Xigmatech Crystal Series fan, White LED. I hooked it up, it is a real neat looking light. The issue I had though, was that my cards (I run dual 4850s) were running hotter with this additional intake fan.

Now, before this fan, I had a negative pressure system with dual 140mm intakes, and 2 x120mm exhaust and a PSU exhaust. The most center of the 3 pushed out a lot of air adding up to a negative system. My system was running at a decent temp but I wanted to make it better because my cards were hitting a lot hotter than I had liked.

Fast forward through the purchase and installation, I am sitting there wondering how on earth this is possible. For a fan that pushes 60CFM of cool air onto the video card, how that can make the card hotter. I would please love for someone to explain this to me.

I turned the fan around to make it an exhaust, and what do ya know, my card temps dropped a few degrees lower than what I was at originally. The issue now, is that because of this, the CPU is a little hotter then when it was an intake. I was so sure an intake is what I needed because the cards are hard to get cool air to being as I have a full tower case. Has anyone gone through something similar? If so, please post results, or any comments on the matter.

 

[Deleted member 184142]

You are running into what I believe allot of people tend to over look...Flow disruption, more fans is not always better, nor is more CFM, a well planned and placed air path is far more productive than brute force. The side fan tossing in air can cause all sorts of turbulence inside the case, you would be shocked at what that can do in terms of air pockets etc.

So, without knowing the case, fan layout and inside wire routing, that would be my guess as to your problem.

 

[Bdonedge]

I have a Lian Li A70F, a thermaltake 120mm back fan and everything else is stock. (and the added 140mm on the side). My cable management isn't bad at all compared to what I used to have (Centurion 5). I'll take some pictures when I'm off work at home to show you what I have.

Do you have any suggestions?

 

[Indeterministic]

BlueFireIce said it well. Air flow is quite a complicated subject, especially when adding in a computer case, all the parts inside, multiple fans, speeds, etc. I went through a few computer cases and several dozen fan layouts before finally settling on something that worked well.

Experiment with as many options as your current system will allow. A quick way to get a positive pressure system is to reduce exhaust fan speed and increase intake fan speed (if it's possible). To manage flow paths inside your case you can experiment with cardboard ducts/barriers until you find something that improves temperatures (doing so can also give insight into what the air is doing). Sometimes reducing air flow altogether or at certain points can show improvements (reducing fan speed or blocking off fans/intakes).

 

[Bdonedge]

Interesting. What benefits are from a positive pressure, other than dust? I'm not worried about dust really because I have an air compressor at my disposal, so I have an unlimited supply of canned air basically.
Eliminating the hot GPU is a task in itself it seems. I'm going to have to try one of those things you suggested Indeterm.

 

[Indeterministic]

Dust and it can help external exhaust systems already in the case a little bit. Either way is generally fine. However, taking it one way or another can create different airflow paths if your case has open air vents so it will depend on your case too.

 

[Deleted member 184142]

Interesting. What benefits are from a positive pressure, other than dust? I'm not worried about dust really because I have an air compressor at my disposal, so I have an unlimited supply of canned air basically.
Eliminating the hot GPU is a task in itself it seems. I'm going to have to try one of those things you suggested Indeterm.

I would not call it positive "pressure" as you are not going to ever achieve either positive or negative pressure in a PC case, there are just to many air inlets and outlets for this to be practical, you might end up with a theoretical higher or lower net input or output. And over all I have tried both setups and have seen little impact from either, and the only real usefulness seems to he in helping out with dust.

But to break it down, the only positive way to drop temps on the GPU's is to get new HSF's for them, you can try replacing TIM and the like on them and see if that helps, but there is only so much you can do inside the case as far as airflow goes to make them run cooler. My first suggestion would be some good quality fans to replace what you have and get more net airflow with the same noise and probably end up with an over all better sound tone. But other than replacing the HSF's on them, you are going to have very little over all impact for the amount of airflow/noise/money you will put into it.

 

[Tudz]

I would not call it positive "pressure" as you are not going to ever achieve either positive or negative pressure in a PC case, there are just to many air inlets and outlets for this to be practical, you might end up with a theoretical higher or lower net input or output. And over all I have tried both setups and have seen little impact from either, and the only real usefulness seems to he in helping out with dust.

You can and do achieve slight negative or positive pressure, that's how air gets sucked in or blown out of holes which dont have fans on them, the pressure difference drives an air flow. This guy with only an exhaust fan shows the case has enough negative pressure to hold up a tissue (lower pressure on one side of the tissue causes a net force on the tissue pressing it against the grill and friction against the grill holds it up).

http://www.overclock.net/air-cooling/748134-negative-pressure-rig-no-case-fans.html

Anyway, its all about airflow. Regardless of positive or negative pressure you just need to make sure fans are set up to cause a good flow of cool fresh air over your components and then exhaust that air out of the case. By nature its easier to achieve in a negative pressure case (its easier to force out hot air and let cool air seep in through the cracks than force in cool air and hope the hot air exhausts).

 

[Deleted member 184142]

You are going to create a negative or positive air flow, but you are not going to achieve any kind of meaningful "pressure" in the case. As fans deal more with high volume than they do with pressure, as fans create a flow within a gas, and deal less with pressure. So you are dealing more with flow, if you did end up with any kind of meaningful pressure change in the case would you would be dealing with some seriously over powered fans.

We can get as "technical" as you like, my point still stands, that neither have any kind of meaningful impact on temperatures and is better to have a well sorted air flow in the case.

 

[Tudz]

You are going to create a negative or positive air flow, but you are not going to achieve any kind of meaningful "pressure" in the case. As fans deal more with high volume than they do with pressure, as fans create a flow within a gas, and deal less with pressure. So you are dealing more with flow, if you did end up with any kind of meaningful pressure change in the case would you would be dealing with some seriously over powered fans.

We can get as "technical" as you like, my point still stands, that neither have any kind of meaningful impact on temperatures and is better to have a well sorted air flow in the case.

Well say you have a case with a single exhaust fan, how does air get into the case? Fan blows air out, lowering pressure inside the case and the pressure difference causes air to flow into the case. Hence why its called negative pressure. It may not be a big negative pressure, it may not be the sort of pressure difference you see on an aircraft wing or in a balloon, but its still the pressure difference that drives the airflow into the case. Pressure and airflow drive each other, you can't say fans deal in airflow without also saying they deal in pressure. Yes, they aren't brilliant at forcing fluid through a high headloss obstruction as say a turbine might be, but you're still dealing in pressure differences.

The reason I said negative pressure is harder to screw up is because you are less likely to cause stagnation points if your fans are set up with negative pressure in mind (you still can, its just less likely).

I haven't tested this, so could be totally wrong, but I suggest if you have a case with multiple fans in different directions turning all of them to blow inwards, causing positive pressure will probably yield higher temps than setting them all to blow outward (its dependant on the case of course, I'm being overly general). I could test it but I really can't be bothered switching all my fans around, and my case isn't the best test bed as mesh over most of it so it probably wouldn't make a lot of difference.

EDIT: Though of course the best thing is simply to have your airflow set up right, but that's generally easier said than done, especially if you have a system with a lot of fan orientation options and fans blowing at right angles to each other, esp. around large obsructions like a high end video card.

 

[rive22]

With a single exhaust fan air is sucked into the case through any opening. Smoke a cigar in front of the case when you tinker with your setups and you'll see how the smoke flows.

 

[Tudz]

With a single exhaust fan air is sucked into the case through any opening. Smoke a cigar in front of the case when you tinker with your setups and you'll see how the smoke flows.

Yeah exactly... coz the inside of the case is a lower pressure than the air surrounding it and a fluid will naturally travel from high pressure to low pressure.

 

[mtrupi]

Don't get too hung up on the pressure discussion. The fans aren't designed to provide much pressure differential. A slightly higher pressure inside can help with dust if the intakes are filtered. That's about it for pressure. As already stated, the side fan is disrupting the airflow design of the case. It's not surprising that there is a give and and take regarding video card and CPU cooling. Changing where you put the side fan, adding baffles to control the flow, and so on. There's a lot of things you could experiment with and it would probably be kind of interesting to do. However, the advice to put a better heat sink on the video card is only sure bet.

 

[Deleted member 184142]

Well say you have a case with a single exhaust fan, how does air get into the case? Fan blows air out, lowering pressure inside the case and the pressure difference causes air to flow into the case. Hence why its called negative pressure. It may not be a big negative pressure, it may not be the sort of pressure difference you see on an aircraft wing or in a balloon, but its still the pressure difference that drives the airflow into the case. Pressure and airflow drive each other, you can't say fans deal in airflow without also saying they deal in pressure. Yes, they aren't brilliant at forcing fluid through a high headloss obstruction as say a turbine might be, but you're still dealing in pressure differences.

The reason I said negative pressure is harder to screw up is because you are less likely to cause stagnation points if your fans are set up with negative pressure in mind (you still can, its just less likely).

I haven't tested this, so could be totally wrong, but I suggest if you have a case with multiple fans in different directions turning all of them to blow inwards, causing positive pressure will probably yield higher temps than setting them all to blow outward (its dependant on the case of course, I'm being overly general). I could test it but I really can't be bothered switching all my fans around, and my case isn't the best test bed as mesh over most of it so it probably wouldn't make a lot of difference.

EDIT: Though of course the best thing is simply to have your airflow set up right, but that's generally easier said than done, especially if you have a system with a lot of fan orientation options and fans blowing at right angles to each other, esp. around large obsructions like a high end video card.

And like I said, you can get as "technical" as you like about it, my point (that is my first helpful point) is that you will not create any kind of meaningful pressure of any kind in the case, and even if you could it would have no effect on temps. Fan's are high volume low pressure, unlike things such as compressors which are high pressure low volume, fans are about flow and trying to be all technical about how you are going to define this is not helpful in the least to the OP and his problems, and I am not going to further try and debate with you that you might be able to create a -0.01kPa inside of a case, the discussion is really very pointless. And as such I will be ignoring any other posts of yours unless you decide to post something constructive to the OP's problem.

 

[Tudz]

Jeeze, no need to get all huffy about it. The OP specifically asked about differences between positive and negative pressure. The relavant part I put in my first post, which is directly related to the OPs problem.... "Regardless of positive or negative pressure you just need to make sure fans are set up to cause a good flow of cool fresh air over your components and then exhaust that air out of the case. By nature its easier to achieve in a negative pressure case (its easier to force out hot air and let cool air seep in through the cracks than force in cool air and hope the hot air exhausts)."