Sign in with
Sign up | Sign in
Your question

AIRFLOW GUIDE - Case Airflow (corrected)

Last response: in Components
Share
March 17, 2008 5:05:56 AM

When it comes to airflow inside a computer case, too many people take it for granted exactly where the air is going to or coming from. In an attempt to shed some light on the subject, here is a basic overview of air movement. We will look at how each fan alters the air flow, and what other effects are seen as we increase the number of fans.

First, lets look at the effect of the back mounted case fan... the single most common and relied upon fan in the system. As we can see the fan does push out a fair amount of air. We can also see that the air that is being pushed out is then sucked in very slightly from every opening in the case. As the air is expelled it creates a vacuum effect inside the case. It is this vacuum that is the only thing bringing air into the case. As you might imagine this does not provide a significant amount of cooling... simply because the volume of air passing through the case is fairly small.

If we then add in the airflow provided by the PSU we can see it makes no overall difference in airflow. At least since we have a lower mounted one. However, if we had a top mounted PSU, then it would be blowing air out of the case, which would then create a bigger vacuum inside the case. This of course, would then draw more air in through all the openings. As a result, the drives would be a little cooler from the added airflow.

Of course no one will run a computer without a fan over the CPU as well. This fan will always be blown towards the closest opening, either up or back. What time means is that the air will be blow straight out of the case. However, what will likely also happen is that the speed of the case fan will slow down. This overall will only increase the airflow lightly because of the added flow from the CPU fan.

As long as the CPU is in a decent temperature range, the case fan does not need to operate at full capacity. Thus, the overall effect is still basically the same. There really is not much of a difference in the overall volume of air flowing through the case. This is a very good thing given that the air actually hitting the CPU fan is a little warmer than normal because of the extra heat generated by the drives.

Now, if we add another fan to the system... this time pushing air into the case from the front, this changes the airflow a bit. Now, the amount of air being drawn into the case through the fans is equal to the volume of air being expelled by the fans. What this means is that inside the case there will no longer be a vacuum created. This in turn will remove the cooling the drives were recieving. This will lower the temp of the air hitting the CPU fan. Yet, in the end the overall cooling effect is actually less.

Now, lets stop for a moment and look at that. We now have more of a straight-through flow of air hitting the CPU fan, which allows the CPU to operate at a lower temp. However, because the drives are not getting any kind of airflow they will not be able to stay cool. This of course will increase the air temp inside the case, but because of the extra airflow we actually do get better cooling. However, we can still do better.


Plus, there is also the issue of harddrives. Up till this point they have been completely ignored. If we add another fan that draws air directly over the harddrives or that blows air into the case over top of them, then two benefits are had. 1) The harddrives now get some cooling happening. Before this was not occurring because there really was no way for the air to flow around the harddrives. And 2) We increase the volume of air being drawn into the case. This in turn increase the volume of air flowing inside the case... which result in the opposite effect of the vacuum. Now air will begin to blow out of the case through all the openings it was being drawn into before.

As a result we actually increase our cooling capacity quite a lot. There is now air flowing around every component inside the case. The drives have air flowing out of the case that is nice and cool because it doesn't have too much time to heat up very much. Since the air is flowing as such a large volume it doesn't need to heat up as much to remove the heat that is within the case.

In the end, this means that the computer as a whole will remain cooler... which we all know increases the life span of all the parts. This then means we can save money by not having to replace worn out pieces as often. Thus, by simply increasing the air flow, we have increased the value we receive from the computer... which we can then also opt to transfer into performance improvements as a result of overclocking... if you so choose.

Now that we have great airflow, what happens when we put in an opening in the side of case to accommodate even more airflow? Well, that depends on what we do with that opening. If we have nothing in the opening, it just allows air to flow freely... then we actually cut off the air that would otherwise flow out past the drive bays. The hole does allow for more air flow, but the only pieces that will benefit are the ones closets to the opening. In essence meaning we actually lose some cooling... even though some pieces are much more cool.

However, if we have a nice big fan in that opening then the situation changes again. If the fan in the opening draws air inside the case then we actually end up with an additional benefit... the air is blown directly on the GPU and around the CPU. This means that those pieces get a little extra cooling... and the net result is that we end up with more air flowing out all the openings... thus cooling the drives even more.

However, if it is blowing air out from the case, then the overall effect will be lost because the air flows straight out from all the areas it is drawn in. The air from the PSU and front of the case will actually be directly diverted to the side fan. This will lower the temp inside the case, which will help to keep the PSU and CPU cool, but will again do nothing for the drives.

Of course, most people won't actually have a bottom fan and a side mounted fan like I have shown... which adjusts the location and volume of airflow accordingly... which I think you now understand enough for me not the have to explain the overall effects.

Now... lets stop for a moment and look at what the overall effect would be on this if we moved the PSU to the top instead of the bottom. Because the airflow here is basically equal in terms of the volume of air being drawn in and the volume being expelled... we cut off the flow to the drives. In the end, this is not as good as if the PSU was down below... but because the case does stay cooler the drives will be able to remain a little cooler too. Since we normally do not punish the drives the same way we do other componenets... in the end this is actually still okay.

CONCLUSION:

What this all means is... it's not a matter of how many fans we have that matters, it's the volume of airflow being drawn in compared to the volume of airflow being blown out, combined with the location of the air flow that matters. Ideally, the best benefit we can get comes from having more fans drawing air into the case (at least one of which is flowing over the harddrives) compared to the number blowing air out... which will allow air to flow out all the openings by the drives.

It also tells us that if we have more fans blowing the air out... we need to make sure there is a decent different in the air volume being blown out. If overall, the vacuum created is not very big, then only a tiny amount of air will flow by the drives... like what we saw when there were only three fans (including PSU). So we really would want at least one more fan blowing the air out up top. Something we could achive by removing the bottom corner fan from the pic with the PSU up top. That would give us enough of a vaccum to keep the air flowing the way we want.

Of course, there are a number of solutions that can be used to increase the airflow in a case that doesn't currently have great airflow. Can try and find a side-panel that will draw air into the case, can get drive fans (fit in a drive bay... though are small fans), or can modify the front of the case to hold a fan (depending on the front of the case of course).

Obviously, use your best judgement if you are going to modify something and make sure you won't be damaging anything else of importance in the process. Plus, the less heat that is produced inside the case, the less cooling that is needed. If you only have a single GPU, harddrive, CD/DVD Drive, and CPU putting out heat, you don't need the same level of cooling as someone who has 4 GPU's, 5 harddrives, 3drives, and an overclocked to the hilt CPU. So adjust your cooling needs appropriately.


Note: Remember... the CPU fan will ensure the rear case fan is not typically running at full speed all the time. Hence, the overall effect of the CPU fan will balance out the case fan in regards to air flow (ONLY). The CPU fan will make a huge difference in the amount of heat drawn away from the CPU... which is why it is essential to have it. It just doesn't do too much with regard to the VOLUME of air flowing through the case.
March 17, 2008 7:01:05 AM

that's grate thanks :D 
March 17, 2008 7:30:52 AM

Don't power supplies usually push air outward?
Related resources
March 17, 2008 8:10:17 AM

That would depend on the unit.

Some, if they are possitioned as in my diagram, could also push the air out the bottom and by-bass the computer alltogether if people wanted to and had the opening for it.
a b ) Power supply
March 17, 2008 8:42:59 AM

I'm thinking of modding my current cheapo case and just having a line of fans along the bottom (sucking in) and the top (blowing out). Possibly with one less top than bottom to take into account my PSU which expels air from the case.
March 17, 2008 9:02:29 AM

lilsage said:
That would depend on the unit.

Some, if they are possitioned as in my diagram, could also push the air out the bottom and by-bass the computer alltogether if people wanted to and had the opening for it.


Actualy you have that backwards, power supplies take air from inside of the case and exhaust it out the back.
When a case allows for it(like in your illustrations) the power supply may take air in from the opening on the bottom of the case and exhaust it out the back.
March 17, 2008 9:15:32 AM

I just updated the pics a bit... made them more clean.

Also... here is what the airflow in my comp looks like... if anyone is curious.


The airflow out the front is what prompted me to create this. Never had a case that ever did that before and thought it was so much better for keeping everything nice and cool. I love my Cosmos 1000 (shameless plug!!!!)
March 17, 2008 9:48:44 AM

evilshuriken said:
Actualy you have that backwards, power supplies take air from inside of the case and exhaust it out the back.
When a case allows for it(like in your illustrations) the power supply may take air in from the opening on the bottom of the case and exhaust it out the back.


Looking further I think you are right. I did this away from home and was working off memory. When I had a look at the bigger version of my avatar pic, there is no fan inside my case at all. It blows from the back down.

I will have to do an update version with the direction changed.

Thanks!
March 17, 2008 11:16:02 AM

lilsage said:
When it comes to airflow inside a computer case, too many people take it for granted exactly where the air is going to or coming from. In an attempt to shed some light on the subject, here is a basic overview of air movement. We will look at how each fan alters the air flow, and what other effects are seen as we increase the number of fans.
http://www.members.shaw.ca/lilsage369/images/case_onefan.jpg
First, lets look at the effect of the back mounted case fan... the single most common and relied upon fan in the system. As we can see the fan does push out a fair amount of air. We can also see that the air that is being pushed out is then sucked in very slightly from every opening in the case. As the air is expelled it creates a vacuum effect inside the case. It is this vacuum that is the only thing bringing air into the case. As you might imagine this does not provide a significant amount of cooling... simply because the volume of air passing through the case is fairly small.
http://www.members.shaw.ca/lilsage369/images/case_twofan.jpg
If we then add in the airflow provided by the PSU we can see it makes no overall difference in airflow. At least since we have a lower mounted one. However, if we had a top mounted PSU, then it would be blowing air out of the case, which would then create a bigger vacuum inside the case. This of course, would then draw more air in through all the openings. As a result, the drives would be a little cooler from the added airflow.
http://www.members.shaw.ca/lilsage369/images/case_threefan.jpg
Of course no one will run a computer without a fan over the CPU as well. This fan will always be blown towards the closest opening, either up or back. What time means is that the air will be blow straight out of the case. However, what will likely also happen is that the speed of the case fan will slow down. This overall will only increase the airflow lightly because of the added flow from the CPU fan.

As long as the CPU is in a decent temperature range, the case fan does not need to operate at full capacity. Thus, the overall effect is still basically the same. There really is not much of a difference in the overall volume of air flowing through the case. This is a very good thing given that the air actually hitting the CPU fan is a little warmer than normal because of the extra heat generated by the drives.
http://www.members.shaw.ca/lilsage369/images/case_fourfan.jpg
Now, if we add another fan to the system... this time pushing air into the case from the front, this changes the airflow a bit. Now, the amount of air being drawn into the case through the fans is equal to the volume of air being expelled by the fans. What this means is that inside the case there will no longer be a vacuum created. This in turn will remove the cooling the drives were recieving. This will lower the temp of the air hitting the CPU fan. Yet, in the end the overall cooling effect is actually less.

Now, lets stop for a moment and look at that. We now have more of a straight-through flow of air hitting the CPU fan, which allows the CPU to operate at a lower temp. However, because the drives are not getting any kind of airflow they will not be able to stay cool. This of course will increase the air temp inside the case, but because of the extra airflow we actually do get better cooling. However, we can still do better.

http://www.members.shaw.ca/lilsage369/images/case_fivefan.jpg
Plus, there is also the issue of harddrives. Up till this point they have been completely ignored. If we add another fan that draws air directly over the harddrives or that blows air into the case over top of them, then two benefits are had. 1) The harddrives now get some cooling happening. Before this was not occurring because there really was no way for the air to flow around the harddrives. And 2) We increase the volume of air being drawn into the case. This in turn increase the volume of air flowing inside the case... which result in the opposite effect of the vacuum. Now air will begin to blow out of the case through all the openings it was being drawn into before.

As a result we actually increase our cooling capacity quite a lot. There is now air flowing around every component inside the case. The drives have air flowing out of the case that is nice and cool because it doesn't have too much time to heat up very much. Since the air is flowing as such a large volume it doesn't need to heat up as much to remove the heat that is within the case.

In the end, this means that the computer as a whole will remain cooler... which we all know increases the life span of all the parts. This then means we can save money by not having to replace worn out pieces as often. Thus, by simply increasing the air flow, we have increased the value we receive from the computer... which we can then also opt to transfer into performance improvements as a result of overclocking... if you so choose.
http://www.members.shaw.ca/lilsage369/images/case_sideopen.jpg
Now that we have great airflow, what happens when we put in an opening in the side of case to accommodate even more airflow? Well, that depends on what we do with that opening. If we have nothing in the opening, it just allows air to flow freely... then we actually cut off the air that would otherwise flow out past the drive bays. The hole does allow for more air flow, but the only pieces that will benefit are the ones closets to the opening. In essence meaning we actually lose some cooling... even though some pieces are much more cool.

However, if we have a nice big fan in that opening then the situation changes again. If the fan in the opening draws air inside the case then we actually end up with an additional benefit... the air is blown directly on the GPU and around the CPU. This means that those pieces get a little extra cooling... and the net result is that we end up with more air flowing out all the openings... thus cooling the drives even more.

However, if it is blowing air out from the case, then the overall effect will be lost because the air flows straight out from all the areas it is drawn in. The air from the PSU and front of the case will actually be directly diverted to the side fan. This will lower the temp inside the case, which will help to keep the PSU and CPU cool, but will again do nothing for the drives.

Of course, most people won't actually have a bottom fan and a side mounted fan like I have shown... which adjusts the location and volume of airflow accordingly... which I think you now understand enough for me not the have to explain the overall effects.
http://www.members.shaw.ca/lilsage369/images/case_toppsu.jpg
Now... lets stop for a moment and look at what the overall effect would be on this if we moved the PSU to the top instead of the bottom. Because the airflow here is basically equal in terms of the volume of air being drawn in and the volume being expelled... we cut off the flow to the drives. In the end, this is not as good as if the PSU was down below... but because the case does stay cooler the drives will be able to remain a little cooler too. Since we normally do not punish the drives the same way we do other componenets... in the end this is actually still okay.

CONCLUSION:

What this all means is... it's not a matter of how many fans we have that matters, it's the volume of airflow being drawn in compared to the volume of airflow being blown out, combined with the location of the air flow that matters. Ideally, the best benefit we can get comes from having more fans drawing air into the case (at least one of which is flowing over the harddrives) compared to the number blowing air out... which will allow air to flow out all the openings by the drives.

It also tells us that if we have more fans blowing the air out... we need to make sure there is a decent different in the air volume being blown out. If overall, the vacuum created is not very big, then only a tiny amount of air will flow by the drives... like what we saw when there were only three fans (including PSU). So we really would want at least one more fan blowing the air out up top. Something we could achive by removing the bottom corner fan from the pic with the PSU up top. That would give us enough of a vaccum to keep the air flowing the way we want.

Of course, there are a number of solutions that can be used to increase the airflow in a case that doesn't currently have great airflow. Can try and find a side-panel that will draw air into the case, can get drive fans (fit in a drive bay... though are small fans), or can modify the front of the case to hold a fan (depending on the front of the case of course).

Obviously, use your best judgement if you are going to modify something and make sure you won't be damaging anything else of importance in the process. Plus, the less heat that is produced inside the case, the less cooling that is needed. If you only have a single GPU, harddrive, CD/DVD Drive, and CPU putting out heat, you don't need the same level of cooling as someone who has 4 GPU's, 5 harddrives, 3drives, and an overclocked to the hilt CPU. So adjust your cooling needs appropriately.


Note: Remember... the CPU fan will ensure the rear case fan is not typically running at full speed all the time. Hence, the overall effect of the CPU fan will balance out the case fan in regards to air flow (ONLY). The CPU fan will make a huge difference in the amount of heat drawn away from the CPU... which is why it is essential to have it. It just doesn't do too much with regard to the VOLUME of air flowing through the case.


This kind of thing makes a really interesting change from intel vs. amd threads. Well done and well written!
a b ) Power supply
March 17, 2008 4:32:07 PM

Personally I would say that if air is being forced out the front of your case as your arrows indicate you need to add either another blowhole to the top, or an additional rear exhaust fan.

My airflow path is a lot different than yours but my case is heavily modified from its standard inefficient stock days anyway, I chambered off my graphics card section and made it enclosed and independent, that stopped it from adding to the heat generated in the case.

The graphics section is supplied intake air from the front added 120mm fan, the case originally was equipped with an 80mm lower intake fan, and I modified the case and changed it to a 120mm, that closed off graphics sections heat is exhausted by a side 140mm fan directly over the graphics section, eliminating the CPU intaking preheated air from the graphic section.

That mod was necessary because unfortunately not all graphics cards exhaust their heat outside the back of the case, and even if they do they still release heat from the backside of the card, and most cases are setup to pull air over the HDDs preheating the air going into the CPU area, thats why I moved the location of my HDDs to below the rear top blowhole, putting them in the exhaust lane instead of the intake lane.

I also moved my P/S outside the case, since it intakes preheated air from inside the case normally, its now intaking normal room temperature air and hasn't the first time even under the heaviest gaming load kicked into its high cooling mode, these case modds have truly made a difference in the overall cooling performance, allowing me to drop my cooling fans extremely low and quiet and still game without any overheating what so ever.

My cpu is fed by another case modded and added additional 120mm intake fan just above the lower front intake, with the baffle chamber plate located between the 2 front intake fans, the 120mm feeds a heavy cardboard air tunnel apprx. 6" in diameter and at the end of that tunnel is a 92mm compression fan that directly feeds air straight into the CPU cooler.

The heat from the CPU cooler is exhausted out the rear of the case by another 92mm exhaust fan, and the 2 top mounted 140mm blowholes, with the rear blowhole dedicated to cooling the HDD carriage, which creates nothing but intake from the front of the case.

Chambering off areas completely changes airflow paths, however these changes require quite a bit of ingenuity, time, determination, and effort to accomplish, its cooler for O/Cing and basically the lifetime of the components, and just flat out more effecient cooling.

Chambering the graphics section was more critical when I was running an SLI setup, the 2 cards produced quite a lot of heat together, though I'm not presently running an SLI setup my future plans will be once again. Ryan


http://i215.photobucket.com/albums/cc165/Ryan_4ryan6/GraphicsChamber.jpg
!