Now that you’ve identified the power contributors, you can focus on how to remove heat from the system. Many thermal contributors either provide no active cooling or vent hot air back into the PC case to be recirculated. This hot air must be vented with a combination of case fans and vent holes.
A major consideration should be convection. Hot air rises, and you can take advantage of this. It’s common to see a fan mounted at the top rear of the case, blowing outward. This pulls air from the front of the PC, usually through vent holes near the bottom. This configuration not only works with convection but also prevents hot air from blowing out of the front of the chassis toward the user. You don’t want to try to pull the air down toward the bottom of the case. This method works against convection and has the effect of pulling risen, hot air back over the hot components.
Much discussion online surrounds inward versus outward airflow, that is positive versus negative pressure. Should a fan be oriented to blow into the case or out of it? Both solutions can achieve the wanted effect if you consider convection and identify hot components. A correctly designed system provides efficient cooling with streamline or laminar airflow. You want this type of airflow because there is little turbulence that recirculates hot air that can cause hot pockets. You can achieve this with positive or negative pressure if there is a clear inlet and output path.
To achieve laminar airflow, you need a clean, unrestricted chassis. If there are any unused peripheral cards, remove them because they only trap heat. For peripherals in use, space them out if possible. Poor cable management can restrict airflow, so tightly bundle or remove unused power cables and connectors. Most PC chassis have some way to use cable ties to secure cables out of the way. Be sure that you’re not blocking an inlet or output vent. There should be plenty of space around the PC. If the chassis is cleanly organized but there is still insufficient air flow, you may need to upgrade to a larger PC case. Finally, keep your PC clean. Dust is an insulator and makes even a well-designed system inefficient at removing heat.
Cool Your System With Fans
You can choose from many fan options, but few are designed to operate at high temperatures or for extended periods. For this reason, you should consider industrial fans for these applications. When looking at fans from reputable manufacturers like ebm-papst, Noctua, and Sanyo Denki, consider the following features.
The fan’s construction material contributes to not only its max temperature rating but also its durability. This affects how well the fan can handle the accidental foreign object inserted while spinning. Typically, high-quality industrial fans contain fiberglass reinforcement that can take the high temperatures and hazardous environments.
Low-cost fans typically contain sleeve bearings that rely on oil/grease for smooth rotation. Over time, the lubricant is lost or changes in viscosity—this is accelerated at high temperatures. Because of the change in lubricant, the fan can fail abruptly and negatively affect the system with little warning. For this reason, you should consider ball bearings. These are sometimes a bit louder because there are moving parts, but they have a much longer lifetime when compared to sleeve bearings. Industrial fan manufacturers have made improvements in both sleeve and ball bearing designs that outperform the standard bearings, making the choice more complicated.
It may be intuitive to focus on fan speed. You may expect a 2,000 rpm fan to outperform a 1,500 rpm fan but that may not be the case. It’s important to look at the cubic feet per minute, or cfm. This merit describes the amount of air the fan can move. Speed is a factor but there are others as well, such as diameter of the fan, number of blades, angle of the blades, and aerodynamic design. That being said, the importance of a properly designed system with efficient airflow trumps the effect of the fan cfm.
You can control fan speed in a couple of different ways, and it’s important to know what types of fans are compatible with the system you are designing. The two main ways are DC voltage and PWM control. For a DC-controlled fan, the speed is proportional to the DC voltage that is applied. Some DC fans provide a signal indicating the fan speed back to the system. For PWM fans, the fan speed is proportional to the duty cycle of the signal applied. These fans provide a speed-indication signal back to the system as well.
Some fans include an ingress protection, or IP, rating. This rating system uses two numbers to indicate the level of dust and water protection. As shown in the figure below, the fist number ranges from zero to six and gives the level of dust protection. An IP5x or IP6x fan is recommended to keep out some or all harmful dust that may cause a fan to fail prematurely. The second number indicates the protection from liquids. This is generally not a concern for computer-based systems since other components would fail in wet environments before the fan. Note that a fan that is IP rated doesn’t mean that it is “high quality.” Furthermore, an unrated fan is not necessarily less protected against dust—it just wasn’t tested and certified to an IP rating.
For particularly dusty environments, you should include dust filters on computer fans. Dust filters keep insulating dust out of the system and extend the lifetime of fans by keeping them clean. The filters, however, reduce the total cfm of the fan and that may warrant using a fan with a higher cfm rating. Consider also adding dust filter material to the inlet holes of the system. It is critical that you clean dust filters regularly. A clogged dust filter can hinder a system’s cooling more than it helps.
The best quality fans are made by companies that stand by their products. Look for fans that have more than a two-year warranty. Some fans come with a warranty of five years or more. It’s even better if the company provides a mean-time-to-failure number to give an estimated interval before replacement. This value is usually given in hours.