For years we’ve all heard the claims that positive case pressure can help reduce the amount of dust entering your PC case. There have been countless opinions stating why positive case pressure is beneficial, but until now there has been no scientific data to prove this hypothesis we’ve run across. Being proponents of empirical testing, and the scientific method in general, Overclockers has teamed up with be quiet! to conduct what could be the first physical testing as to whether positive case pressure really does reduce dust in your PC.
We should start by thanking be quiet! for providing the necessary components for making this test possible. The combined costs of these components would have prevented the article from ever getting started. Donations include three Pure Base 500DX mid-tower cases, three Pure Power 11 500 watt power supplies, and three Dark Rock 4 CPU coolers.
What is Dust?
Whether you like it or not, dust will accumulate in your house. It is an inevitable fact, and according to an article by Page’s Personal Cleaning, bedrooms and living rooms are the most susceptible to dust formation. Unfortunately, this is also where a majority of computer systems reside in the home. So, what is dust, and where does it all come from? Dust is primarily comprised of dead skin, hair, pet dander, fur, pollen, blowing dirt, sand, bacteria, mold, textile fibers, dust mites and their excrement, and decomposing insects. Due to the nature of its contents, dust is highly varied by different regions of the world, even neighboring houses will have vast differences in their make up.
Dust is not just disgusting, it can cause a multitude of problems for your computer. Over time it builds up in heatsinks, radiators, and fans, severely reducing the effectiveness of these cooling devices. It can also create catastrophic shorts in electrical circuits like the motherboard, graphics card, or power supply. So how do we stop it?
“An ounce of prevention is worth a pound of cure.” – Benjamin Franklin.
Naturally, this famous American Statesman wasn’t referring to dust prevention, but this idiom is certainly applicable. Housekeeping is the best way to keep dust from collecting in your PC case. Replacing house furnace filters with High-Efficiency Particulate Air (HEPA) filters and frequently vacuuming carpeting will greatly reduce the amount of dust in the air. Many vacuums come equipped with HEPA filters as well. Finally, your PC chassis is the last line of defense. Fortunately for us, nearly all case manufacturers are on board with dust prevention and come equipped with filters designed specifically for dust prevention while allowing maximum airflow. Keep in mind these filters will need to be cleaned regularly and are generally designed for easy removal.
Pressure vs. Airflow
Airflow is an easy concept for us all to grasp. We’ve all sat in front of a fan and enjoyed the cool breeze it provided. Air pressure, on the other hand, is not as easy to visualize. It’s all around us, even now as you read this article, there is a barometric pressure applying force to your hands, feet, and eyes. Normally, our bodies aren’t very sensitive to it. It isn’t until you get a head cold or other ailments that you can really feel it. But it is there, always.
Fans create pressure and airflow by spinning its fan blades at high speeds moving the air. The airflow is measured in Cubic Feet per Minute or CFM. The pressure is also measurable, though it’s not quite as easy to explain. When related to fans, generated pressure is sometimes called hydrostatic pressure or just simply static pressure, and its unit of measurement is millimeters of water or simply mmH2O. Hydrostatic pressure is defined as the pressure exerted by a column of water of 1 mm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity. I warned you there was going to be science here.
So why all the technical talk? It turns out that, although airflow is a product of pressure, the two have very different applications. Airflow is essential in removing heat from within a PC’s chassis: static pressure, on the other hand, is not. Its role is best served when the fan is mounted directly onto a radiator or other heatsink with tightly packed fins. A great way to visualize the difference is static pressure is the force that pushes air (through the radiator for example), while airflow is the volume a fan can move. Since the testing environment isn’t a closed chassis, we use the term ‘pressure’ loosely throughout this article. So this raises the question, do case fans produce enough pressure or airflow to affect how much dust enters the PC? Let’s test it and find out.
Testing the hypothesis that positive case pressure reduces dust presented several unique challenges. First, how can this be done promptly? Nobody wants to wait an entire year to see if a hypothesis has merit and to be honest, I’ve been hoping to conduct this test for several months. While waiting to hear back from several potential sponsors and other behind the scene events, nearly six months’ worth of dust had been collected.
Secondly, a means of containing all that dust during actual testing and not allowing it to re-enter the household was paramount. Some type of dust containment chamber was a necessity, and that is exactly what was constructed. The frame is built from wood and features a cardboard floor. Plastic sheeting and a whole lot of duct tape wrapped around the entire structure and what we end up with is the opposite of a cleanroom. A hole was needed at the top near the front to allow for all the dust to be added. At 29″ tall, 37″ wide, and 43″ deep, the dust chamber has an internal volume exceeding 26 cubic feet. This will do perfectly.
Since every household contains a wide spectrum of dust particulates, the testing was conducted in two phases. First, the collected dust was filtered through a standard window screen to eliminate any large particles and was allowed to run its course through the chamber. This dust represented the fine particles that are most common in a variety of homes and is what you generally find when cleaning your PC. Periodically, an air compressor was used to kick up the dust to ensure as much entered the three cases as possible.
The second phase utilized a larger particulate of filtered sand and sawdust. This larger and heavier particulate represents computer systems that are located in the dry arid regions or in workshops of various types. Like the fine dust, this was added a little at a time, frequently using the air compressor to make sure all three rigs had a fair chance at collecting this larger particulate.
Now for the computer builds; how do we eliminate the great number of variables? With the large variety of cases in the world and an even greater number of case fans, all having different CFM ratings, it was critical to complete three identical builds and reduce as many of these variables as possible. We are very fortunate to have be quiet! partner up with us for this project and provide the bulk of the components. In addition, Overclockers.com provided three additional Pure Wings 2 140mm case fans to complete the builds.
The installed motherboards, memory, and graphics cards are non-functional and added simply for mounting the air coolers and simulating typical airflow scenarios. As the fans are different on each of the GPUs, they were not provided power, therefore maintaining consistent conditions. Each build utilizes four 140mm Pure Wings 2 case fans which each generate 61.2 CFM at 900 RPM, for a combined total of 244.8CFM per build. The only difference between these systems is the location of the intake and exhaust fans. Every fan, including the CPU cooler, is powered directly from the power supply to maintain 100% power throughout the testing process. Intake filters were left in place while all exhaust filters were removed. This will best simulate a real-life scenario.
Intake Heavy Build
The positive pressure build has three intake fans and a single exhaust. Two intakes fans are located at the front of the case with the third at the front of the top. The single exhaust is, of course at the rear. Each Pure Wings 2 140mm fan generates 0.76 H2O of air pressure which gives the positive pressure build an intake to exhaust pressure ratio of 2.28:0.76 H2O or a +1.52 H2O positive pressure. In theory, this positive pressure will allow air to escape the many case vent holes and in the process prevent dust from entering. Since the intake fans are located at the front and top filters, most of the dust should get collected there making clean-up a breeze.
Neutral Airflow Build
There are two intake and two exhaust fans in the neutral pressure build providing a near balanced pressure ratio of 1.52:1.52 H2O or a +0 air pressure. True neutral pressure is really a fallacy as it is nearly impossible to create an absolute balance of pressure (with the tools we have available). The main variable being the resistance the fans experience pushing or pulling air through the filter and case mesh. However, for argument’s sake, we will call this build neutral as it is as close as possible. With this set-up, there are the same two front intake fans and rear exhaust fan, but the top fan is moved to the rear of the top and installed to exhaust. With a balance of intake and exhaust, there should be little to no air flowing through the holes that are not occupied by fans. Theoretically, this too will force all dust entering the case to pass through the front intake filter.
Exhaust Heavy Build
For the negative pressure case, we located a single intake fan in the middle of the front and three exhaust fans at the rear and top of the chassis. This creates a negative pressure ratio of 0.76:2.28 H2O or a -1.52 H2O air pressure. The major theoretical concern with this type of set-up is, with negative pressure inside the case, air and dust can be sucked into the unfiltered ventilation holes.
You can see right away that these builds were placed in an absolutely brutal environment. No computer should ever be tortured to this extent, but in the name of science, sacrifices must be made. The testing was conducted for approximately 50 hours and was terminated when several fans developed a loud clicking noise. For safety reasons, it was decided to ‘pull the plug’ before too much dust accumulated in one of the power supplies, creating a potential fire hazard. With the testing concluded, we can finally compare the three different results. Keep in mind this testing was conducted in an extreme condition and would more closely simulate years of neglect, rather than a few days, weeks, or months.
Intake Heavy Results
Starting with the positive ‘pressure’ case we can see the outside of this case is literally coated with sand, sawdust, and house dust. The front filter prevented quite a bit of the small particulate from entering the case. Looking inside we can see plenty was still able to enter and collect on the air cooler, fans, and other internal components. All the large particulate was collected at the bottom. This type of dust has more weight and lacks the ability to attach to the upper components. A cotton swab was used to wipe a small area clean to show how much of the larger dust was able to enter.
Neutral Airflow Results
Here we see the results of the neutral ‘pressure’ testing. Again the front filter does a great job of collecting the small particulates but there is a portion that still makes it through and attaches to the air cooler, fans, and other internal components. Looking at the bottom, we find the larger particulate collected in the same manner and location as in the positive pressure case. In fact, the results are nearly identical. If it weren’t for the different internal components it would be difficult to tell these cases apart.
Exhaust Heavy Results
Finally, we look at the negative ‘pressure’ case. Surprisingly, the front filter blocked about the same amount of dust with only a single fan as opposed to two fans. Looking inside and the results are eerily similar to the previous two test subjects. Both the small and large particulate dust collected and attached in the same fashion as the others.
Comparing the three results side by side allows us to conclude it really doesn’t matter if you implement a positive, neutral, or negative pressure system for these chassis’. Just be sure all your intake fans have filters, preferably the fine mesh type that is designed for the small particulate dust. This test also concludes that there is no substitute for regular cleaning.
At this point you may be wondering how these results can be so similar, surely there was an error in testing. Well, the explanation will require two laws of physics. The first states that air reacts in a similar fashion as fluids. While the second is more commonly known, and it is that fluids will naturally flow in the path of the least resistance. Both of these statements are at play here. While the case with more exhaust will intake air from the unfiltered vent holes, the single intake fan creates the “path of least resistance” and therefore the majority of its intake air will pass through the front filter. Naturally, the opposite is true in a case with more intake than exhaust. The single exhaust fan provides the easiest path for the air to escape and therefore most air will exhaust out of the back of the case.
It is through empirical testing and the implementation of the scientific method that we can finally lay to rest one of the oldest debates in the computing community, at least for this chassis and configuration. While these results are for this specific chassis and configurations we would expect similar results from other cases as well. Whether you use more intake than exhaust, around the same, or more exhaust than intake, so long as all other variables are the same, they will all allow approximately the same amount of dust into the PC case. Whether you normally fight with small particulate house dust, the heavier sawdust, or sand from the arid western United States, the results will all be the same. This myth is busted.