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Thread: Blowing In The Wind3327 days old

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    older, but still not wiser keldon's Avatar
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    Blowing In The Wind

    Blowing In The Wind
    All About Case Fans

    Cooling the various components of a case by the use of fans, also known as active cooling, is not rocket science. It must be taken seriously though, and carefully thought out, especially if you plan on overclocking or you are using a non-standard case.

    The basic idea is that air enters the front of the case and is then drawn over the components, exiting out the back. This is called forced convection. This setup generally holds true for all types of computer cases but can be achieved many different ways depending on the placement and number of components, the size and number of fans, and whether or not this is a custom case or off the shelf dime store special.

    There's No Pressure Here

    There are three types of forced convection: positive pressure, negative pressure, and neutral pressure. Each one of these has drawbacks and should only be used under certain conditions.

    Positive pressure is mounting one or more intake fans in the front of the case, thereby forcing air into it. This creates a small amount of atmospheric pressure within the case . The air is then forced out the back through vent holes. The nice thing about this type of a setup is that by only bringing air in through the front of the case you could use a filter to trap most of the dust. As with any sort of filter though, you will have to choose the material wisely so as not to impede the air flow too much. The downside is that any heat generated from the fan will also be carried into the case. This is minimal though and should not cause any real problems.

    Negative pressure, also known as evacuation cooling, places exhaust fans at the back of the case, drawing air into the case through front vent holes. This would eliminate the problem of the heat generated by the fans but dust will be a factor. You can use a filter material but that would cut down on the efficiency of the fans and could also cause airflow problems within the case. When using this type of setup you will create a small vacuum within the case. Like the positive pressure setup up this will create atmospheric instability.

    Air pressure will always try to equalize itself by the easiest method available. With the positive pressure setup, the hot air will flow out the back of the case into the lower pressure. This works the same as opening a can of soda. In order for this to work well though, you need to move a lot of air into that case. With a negative pressure setup, cool air will continually rush into the case to equalize the pressure. I feel this is the best for a properly set up case, but you need to make sure you move more air out than in, or it won't work very well.

    In a neutral pressure setup, intake fans are placed at the front of the case and an equal number of exhaust fans are placed at the back of the case. This also may create a dust problem depending on how you set up the fans and what kind of filters you use. Also, don't forget about the decrease in air flow.

    When using this type of setup you want to remember that it is important to move the same amount of air out of the case as you bring in. This does not necessarily mean the same number of fans, as different size fans move different amounts of air. Air flow is measured in CFM (cubic feet per minute) for these purposes.

    A Bahama Breeze or a Kansas Tornado

    How much air flow is enough, for that matter how do you measure the airflow? When you look at the spec sheet of a case you may see things like: Comes with three 30cfm fans, or comes with two 92mm and a single 120mm fan. What does that all mean, and how will it keep my brand new FX-60 from becoming a hot plate at the next family gathering?

    CFM stands for cubic feet per minute and it is just a measurement of the airflow provided by a fan. The amount of airflow depends on many things but all you need to worry about is the fan speed and size. What does this mean to cooling? To know that you first need to know how many cubic feet are in your case.

    For our example lets take an Antec P180. This is a very nicely designed case and many people use it as a basis for simple mods. The measurements of the case are 21"(H)x8"(W)x19"(L). That makes it a fairly large case to cool, but it also means we have plenty of room to work with. When finding the cubic feet of the case you want to add the three numbers together and then divide by 12. Here we have 21 + 8 + 19 = 48. When we divide that by 12 we get 4 cubic feet. That is the interior space of the case, known as it's volume.

    Now that we know all these fancy numbers lets do something productive with them. Lets say that you have two 50 CFM case fans and a single 60 CFM exhaust fan on the PSU. When you add these together you get a total CFM of 160. That is how many cubic feet of air per minute you are moving around the case. When we divide that by the number of cubic feet in the case you get 40. This means that all your fans, if running at full strength with no problems, will change the air in your case 40 times per minute. Not bad, but the cooling effect depends on what you have in the case.

    To judge for yourself if this is good enough you will need to measure the temperature of key components in your case. If they are not cool enough then you either need to increase the amount of air flowing into the case or you may just need to tidy things up around a specific area such as the hard drive or the PCI slots. Both of these are out of the way areas that may require special attention.

    If It's Too Loud Then It's Too Small

    Fan noise is a concern to a lot of people. They want good cooling but don't want to listen to a 747 under their desk. The new fans that have come out in recent years have made some vast improvements but there are still a few things to keep in mind when choosing a fan for a case that you want to be as quiet as possible.

    The average computer case is usually between 30 and 50 decibels (dba). As a reference point, human speech is normally around 60 dba and damage to your hearing starts to occur at around 85 dba. On most fans there is a dba rating either on the dust cover or on a sticker, right in the center of the fan usually listed next to the voltage rating. Other times it comes on the packaging. The dba rating on the fan will not be entirely accurate though. As a general rule, the fans are tested and rated outside of a case, so you will have some quieting effect depending on where the fan is placed within the case. The bulk of the noise from the fan comes from the bearing assembly, not the aerodynamics, so try to keep this in mind when looking for quiet fans.

    It is a common misconception among some people that the larger fans are noisier than the smaller ones. This is false for the most part. Some of the bigger fans do sound like a hurricane, but most are significantly quieter than the smaller ones. A fan's job is to move air. The larger the surface area of the blades, the more air it will move. A larger fan can move more air just because of its size, therefore it does not need to spin as fast, which means it creates less heat and is quieter than the smaller ones.

    Don't Lose Your Bearings

    The type of bearings that your fan uses should also be taken into consideration when shopping around. It will either be a sleeve type or a ball type. These two styles are very different and each has a strong set of advantages and disadvantages.

    Ball type fans generally have a longer life than the sleeve type but they are inherently more expensive because of this. This is mainly due to the fact that the ball type fans are built to exacting, high tolerances. They have a far greater resistance to heat, and are quieter at higher speeds. These high tolerances also mean that the fans can be mounted in any way, whereas the sleeve type fans can only be mounted vertically.

    Sleeve type fans are much louder at high speeds, mainly due to the sometimes cheaper methods of construction and manufacturing. This makes them less expensive, which is an advantage too, though. Another advantage of the sleeve type bearings is that they may be more rugged. The higher tolerances of the ball type mean that they are much more prone to breaking or going out of alignment if moved around too much. You can actually destroy a ball type fan just by dropping it on the ground.

    A good solution for the general builder is to mix them up. I would use a ball type fan on mission critical components such as the CPU and GPU (the processor on your graphics card). I would then use the cheaper fans for cooling the rest of the case as you will need them in higher quantity. If you do a lot of LAN parties, or often move your system around, then I would strongly advise to look into using all sleeve type fans or at the very least keep a spare fan with you at all times in case you have one fail on you.

    Keep Your Cool

    There are lots of things that you can do with your fans to enhance their cooling capabilities and help bring down the overall temperature of your rig. One of the core components is the CPU. If that overheats you may be fried. One way is to install a separate exhaust fan near the CPU on the back of the case, to pull air away from it and push it outside the case. You can also create or buy small tunnels or channels to funnel the air to an exhaust fan placed on either the back or the side of the case. I recommend the back of the case.

    The middle of the case always seems to get cluttered up with spare IDE cables. This can seriously hamper the air flow of a case and prevent cool air from reaching critical components like the GPU or hard drives. If you are lucky enough to have SATA drives then you don't have much to worry about as the data cables have small surface area, but for those who have the older style ribbon cables, you can buy round IDE cables that will greatly enhance not only the look and cleanliness of your rig, but also allow cool air to reach all areas of the case.

    Note that poor quality round cables can be subject to cross talk interference, which can cause data corruption on high speed IDE connections, so don't be a cheapskate. Alternatively you could use a round cable for your optical drives and tuck your wide hard disk ribbon cable out of the way (e.g. along the side of the case), if length permits.

    You can additionally utilize a tunnel here to pull air from a GPU or any other area of the case. Just install a powerful exhaust fan in the side of your rig and use it to pull heat from the designated area.

    I Feel The Need...The Need For Speed

    Fan controllers are not a necessity but they do have a lot of good things going for them. They can do wonders for controlling the noise of your rig. At night when you crash or at times when you are not using the computer, you can turn the speed down and quiet her down some.

    The controllers are not as complicated as they first may seem. They simply take a singe power input and split it up into a number of outputs, usually between 2 and 4. They work on a very simple principle. The less power you send to the fan, the slower it will run. The main difference between different types of controllers, besides all the extra features they provide, is the variance of the voltage that they allow.

    Some fan controllers allow you to completely cut off the voltage, thereby turning the fan off. Others only allow you to drop it to a certain level. This can come in handy if you run extra fans that are not needed all the time and you only want to run them when under a load.

    With this new found insight into the wonderful world of hot air, I hope you have a better understanding of some of the basic principles and methods used to cool that chunk of sand at your feet.
    Last edited by keldon; 02-10-2007 at 01:04 AM.
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