Configuring a Dust-free Cabinet

[lordirecto]

I have been thinking about ways in which I can reduce dust deposition in cabinets. This article is my attempt to put my thoughts and logic into words, and I feel that my idea(which is extremely vague) will have noticable effect if not a drastic one. Do feel free to ask for any clarifiactions and also tell me if I have made any kind of mistake in it.

Basic Logic:
This is the basic logic that prompted me to think further about applying this logic to cabinet. It is as follows:
All aircrafts need to maintain a threshold of pressure when flying at high altitudes, internally. This pressure has a purpose, which is, to keep all the passengers comfortable so that everyone feels that they are at sea level. When this pressure drops, you will be able to feel it effects which can range from reduced hearing sensitivity to pain in your ears. The same phenomena can happen to people when they are travelling down from a mountain. So, in short, the pressure between a human being's internal pressure and the external atmospheric pressure has a large impact on every human.

Pressure logic in a Cabinet:
NOTE: Please do not assume that I will ask you to place your cabinet in a pressure chamber.
Every cabinet has to have air flow that will circulate within the cabinet and then dissipate to the exterior. In this process, the fresh air that is drawn in is forced to remove the heat produced by the various components that are present within a cabinet, by the process of conduction. This process is always present and is perpetual as long as there is air to circulate.

The pressure inside the cabinet is the amount of air that is drawn into the cabinet, which I intend to call Cabinet pressure. The pressure that exists outside the cabinet is the normal atmospheric pressure, can be called External pressure.

Now the Cabinet pressure is created my fans in a cabinet that draw in fresh air from outside, which is very obvious. This same cabinet pressure is reduced be fans inside the cabinet, which push the air to the outside.

Understanding Dust Accumulation:
I am sure many of you would have opened your cabinet after every few months to find that your cabinet has more dust than our Indian streets, and I am sure many of you are frustrated about the amount of dust your cabinet is able to collect.

According to the logic I have mentioned above, there are two ways that air gets into your cabinet and leaves, which most of you will assume are the only ways that your cabinet collects dust. You are correct to some extent, but there is a third way too!

The third way that air/dust enters your case is through passive openings present in your case. Now our objective is not to seal off all the passive openings so that dust cannot enter. Do note that dust does enter into your case along with the fresh air that you intake fans, and the same dust also exits your case through the exhaust fans. But some of the dust stays behind and settles in your cabinet, which you have to deal with no matter what cabinet you have got.

The first and second way of dust entering your cabinet can be controlled if you can device ways to inhibit dust from entering. It is the third way that cannot be controlled easily.

Controlling the Third:
Recall the two terms Cabinet pressure and External Pressure, as these are the ones you need to befriend.

Here are the three cases which explains the amount of dust accumulation:
1. When the amount of air your cabinet takes in and exhausts are equal, Cabinet pressure equals External pressure and the passive air intake is balanced, but the amount of dust accumulation is not reduced. This is neither worst case nor best case. But this is not the most effective way to reduce dust accumulation.
2. When intake air is lesser than exhaust, Cabinet pressure is lesser than External pressure and results in high passive air intake. Here more air is flowing through the cabinet and so more dust gets into the cabinet. This is the configuration that most people use, thinking that more air flow will give better results, which is true as long as dust does not accumulate. Hence this is the worst scenario to get your cabinet and components into.
3. When intake air is higher than exhaust, Cabinet pressure is higher than External pressure and the results become astounding. Once the Cabinet pressure gets higher, the exhaust fans start to work at their optimal air flow as they get more than abundant air to push out. Also the passive air flowing openings in you cabinet starts to act as exhaust. This keeps out air from entering, which inturn reduces the amount of dust that can enter. This is what you want to achieve, and this is what you need to implement in your cabinets to make your life easier and to decrease your cabinet maintenance. Hence this is the best scenario and is to be preferred the most.

Achieving Results:
I have not been able to come up with a precise calculation of calculating the air flow in your cabinet, and so this is going to be hitting around the bush kind of work. You are the one who will judge your cabinet's airflow and so you are the best judge of what you do.

1. Inorder to make sure you get a reasonable and gaugable idea of what you need to do, try and get an idea of all the fans that you are using in your cabinet and how much air flow it offers. The standard unit of air flow measured in computer cases is CFM-Cubic Feet per Meter(I'm not exactly sure about the expansion).
2. Calculate the total amount of intake air, by all the intake fans.
3. Calculate the total amount of exhaust air, by all exhaust fans. This includes even the fans that comes with the PSU.
4. You now need to remove all the air filters that are present against the exhaust fans, this will give you an uninhibited flow of air, which inturn translates to better efficiency.
5. Factor in the amount of air that all intake fans are able to provide when the intake filters are mounted. Here you have to use your best judgement.

Place your hand in front of the blowing end of the intake fan when its filter is removed, observe the amount of air flow. Now place the air filter and once again observe the amount of decreased air flow. Try to come up with a percentage for the difference, ofcourse with your best judgement.

Calculate the amount of air flow,

Effective Cabinet pressure = (Total intake CFM(point 2) - Percentage of CFM decrease(point 5)) - Total exhaust CFM

If the resulting number is positive to a very small margin(like 1-3 CFM), then you can consider increasing your intake CFM as you have an acceptable Cabinet Pressure.
If the resulting number is positive to a large extent(like 6-11 or above), then you have a optimal Cabinet Pressure.
If the resulting number is negative to any extent, then you have to reconfigure your fans, as you have a negative Cabinet Pressure.

Clarifications: [I intend to update this section as people ask more questions]
1. Many people will say that the increase in Cabinet pressure, which translates to reduced exhaust air can affect cabinet temperatures:
Note that you are not trapping all the air that get into your cabinet. You are only configuring your cabinet fans in such a way that the air that comes in goes out slowly, instead of being a runaway train. This method is only to help you contain/reduce the accumulation of dust by preventing passive air circulation through your cabinet.

2. Air spiralling in your cabinet.
I have mentioned that air is spiralling in the inside of your cabinet, which I am sure many people will question me. Inorder to show you what I specifically mean, I think a visual idea will be best to clarify any doubts that people will have.
I found this video of a HAF X cabinet owner who uses dry ice to do some airflow benchmarking, in youtube. Here is the link: Click Here
Here is a video that shows how different fans push the air in different directions.
[YOUTUBE]8m8fC809TK0[/YOUTUBE]
NOTE: It takes me a long time to research the questions posed by people in real life, to confirm the same details described. So please bear with me for my delayed replys, as I do not want to give away any misinformation.

UPDATE: [10 March 2012]
After an year of usage of my Cooler Master HAF 942, I have found that having just one exhaust and more than 1 intake produces best results. For the past year, I have cleaned my cabinet only 4 times. And I found less than 1mm of dust every time. Here are some pics as to how I have configured my fans.
*img526.imageshack.us/img526/56/996d38f817b4ba74e4c38fb.jpg
*img641.imageshack.us/img641/5941/330507.jpg

 

[venram87700]

gr8 idea and a gr8 theory lord
i just had a few questions though it may seem obvious bt i may be asking questions that others may not or may be thinking them selves
1. what type of a fan config wud u recommend wat i mean to ask is so we need to have fans at the front of the tower to get the optimum flow of air.
2. some ppl also have the habit of placing their towers inside an enclosed cabinet thinking that it will prevent dust from entering the tower (alas that is nt the case n i proved it to my frnd when he told me that he was confident that his tower did nt hav any dust bt when we opened it we found dust deposits to put the streets of mumbai to shame )
3. also as hotter air tends to be lighter than cooler air do the fans that exhaust the heat out need to be placed relatively higher than the intake fans ??

 

[lordirecto]

1. what type of a fan config wud u recommend wat i mean to ask is so we need to have fans at the front of the tower to get the optimum flow of air.

I am working on some pictures of cabinets to illustrate what kind of fan arrangements will give you maximum airflow, but minimum dust intake. Please give me some time so that I can give a reasonably good idea in the form of pictures.

2. some ppl also have the habit of placing their towers inside an enclosed cabinet thinking that it will prevent dust from entering the tower (alas that is nt the case n i proved it to my frnd when he told me that he was confident that his tower did nt hav any dust bt when we opened it we found dust deposits to put the streets of mumbai to shame )

You are correct. Placing a cabinet within an enclosed space does not mean it will keep out dust. Your friend's idea might work only if he can operate his computer in a "clean room", which is not possible for our every day lives, sadly.

3. also as hotter air tends to be lighter than cooler air do the fans that exhaust the heat out need to be placed relatively higher than the intake fans ??

No, intake and exhaust fans can be placed any way. This does not matter because for the very reason you have mentioned, hot air raises. Even if you have a top intake fan, the warm air from your components will find a way out through passive openings around your case. But this is not usually used as we usually feel that top is for exhaust, no matter what. This is because we tend to think to a very straight and simple extent that we forget an important aspect, turbulence. As air is invisible, we cannot see any turbulence at all what so ever. But the way air moves inside of the cabinet is completely different from what we can even imagine.

To keep things short, every object that moves creates turbulence behind it(heard of air packs making a aircraft unstable?). And we have atleast 2 fans even in the lowest end computer. So try to think of the amount of turbulence that your cabinet can generate.

I do hope you are able to create a picture in your mind.

Ofcourse you can counter my answer by taping/sealing all the passive openings. But that will not prove beneficial for your components inside your case.

EDIT: It just occured to me, try and hold a incense stick inside your cabinet, with or without the side panel. Do the same to every fan(in front as well as behind) you can reach. Tell me what you observe.

 

[Gaurav Bhattacharjee]

Ah, reminds me of the P(Total) = P(in) + P(out) concept.

 

[lordirecto]

^ What formula is that exactly?

 

[asingh]

@OP:
Nice analysis. Advice me.

1. Intake 1000 RPM [FRONT]
2. Intake 3000 RPM [SIDE PANEL] - Scythe Ultra Kaze
3. Exhaust 3000 RPM [SIDE PANEL] - Scythe Ultra Kaze
4. Intake 2000 RPM [BOTTOM]

All 4 are on a fan controller. 2,3 are currently runny at 1500 RPM.

?

 

[lordirecto]

@asingh:
FYI: I can tell you that Scythe Ultra Kaze is a fan that can easily push a lot of air. But the problem is that most of the air gets pushed like a cone(the cone's tip is near the center of fan blades). Most high rpm fans have this problem, which can be rectified by using a shroud. So most of the air will be blown towards the sides of your case, regardless of the case you have.

I see that your case is CM 690. What kind of fan does your gfx card have? Is it a stock fan or a redesigned fan?
If it is a stock fan, then your bottom fan is doing a great job(read the FYI above to understand why).

From the images of CM 690 that I can see in google, your cabby does not have too many passive openings. So I feel that it is safe to assume that your 690 is like a pressure cooker now, you have enough intake air to get a high cabinet pressure.
To verify this, are you able to feel warn air raising from the air vents on top? Have you removed all the aluminium screens that are present in your 5.25" drives? If so, you have increased the passive openings. Do your intake fans all have air filters? If not, then all intake fans are sucking in a lot of dust.
You must have reasonable results now, but if you want to see if you can increase(read decrease dust) performance, I suggest you lower the exhaust rpm to 1300-1000(if possible).

But I really dont think that you need to push any futher, but it is worth a try to squeeze every ounce of performance from your cabby.

 

[asingh]

^^
Thank you for the comprehensive and detailed reply.

My HD4890s (2 of them, since am running XfireX) have standard shrouds. You can see the image here. By the bottom fan, I meant it is next to the bottom mounted PSU. Yes, right now both the Scythe Ultra Kaze's (side intake, and back exhaust) are running at around 1500 RPM. The front intake is at 1140 RPM, and I have kept the bottom intake OFF. For some reason this last fan sucks in a lot of heat.

Also have you accounted that my HSF has two fans in push pull..? During hight summers I run the exhaust back Scythe at full 3000RPM. Sounds like a jet.

Any other advice. The XfireX changes the dynamics totally.

 

[lordirecto]

@asingh: Sorry for my belated reply, I got swept off into other things once my LED LCD TV arrived.

For the matter at hand, I did not take your HSF into account at all. I only noticed that you have a Noctua NH-D14 after you specifically mentioned it.
Can you please clarify? You are telling that rear is a exhaust? Does that mean you have an exhaust fan on the side panel too?

As for the gfx cards, most of the hot air gets pushed to the rear by the card fans itself. But that does not mean 100% of the hot air, as there will be some leakage no matter what. The leaked air will surely be sucked into your HSF, which cannot be avoided. So from what I am able to imagine, your computer case is like a wind tunnel(if you have a rear exhaust), not a pressure cooker

Assuming you have an exhaust in the rear of your case, then it is best to make that rear exhaust the only exhaust. That way, the hot air from your CPU as well as those that arise from the gfx cards get pushed back via your HSF. So basically you are trying to control a run away effect that can easily get created.

Let me know what you think.

EDIT: If you want to improve the temperature of your gfx card that is near the proccy, then you can add a intake fan on the side panel that will be on the same level with the gfx card fan.

 

[asingh]

^
The Noctua has two fans. One pulling one pushing. And behind that is another Sythe Kaze at 3000RPM (now) for exhaust. This is the rear cabinet one. This is the only exhaust as of now, apart from the 2nd Noctua fan.

 

[lordirecto]

@asingh:
Your cabinet should be doing fine. I do not see any noticeable complications that maybe able to arise.

Here is something that I think will help you. Placement of you cabinet in your room will greatly influence the amount of dust. Try to find out the paths of air drafts in your room. Remember the following 2 points,
1. Air drafts that come from other room are more likely to bring in a lot of air/dust along with them.
2. Your exhaust air needs to freely move away from your cabinet, else it will spiral back to your cabinet and is likely to bring back the dust.

As for placing the cabinet, if you have a dusty room, then placing it on high level/altitude will reduce your dust intake.