How airflow works inside of a server

 

Computing equipment is notorious for generating heat and servers can pack some very powerful equipment. Because of this, knowing as much as you can about airflow is essential to managing a server rack. 

Even up to the data center level air flow works the same, albeit, managed with different mechanisms. 

Server heat dissipation 

Silicon chips in processors, motherboards, and almost every other computer component generate heat at a rapid rate when under load. Because of this (and unrelated reasons) silicon itself is never exposed and is always covered by a heat spreader.

Internal Heat Spreaders (IHS) are the first level of heat dissipation. The more powerful a chip, the less an IHS will be able to manage heat. All non-mobile CPUs and GPUs will have some kind of heat sink attached to them. This is essentially a bigger chunk of metal that spreads out heat to a greater extent. 

For low powered chips, like in a Macbook Air, the heat sink is enough for cool the CPU while browsing the web. Servers on the other hand will need a fan in addition to the heat sink. On top of that, the fan needs to have access to airflow. 

In summary, your server manages heat for different components in different ways. GPUs and CPUs will have an IHS, heatsink and fan while chips on the motherboard and RAM will only have an IHS. Heat sinks are also used for chipsets and VRMs on a motherboard.

Server chassis cooling design 

Even if all of the cooling mechanisms are in the right places inside of your server, there needs to be air running through it. In the video above, the YouTuber stress tested a computer with no fans other than those on the CPU and GPU. The result was a GPU that ran at 93 degrees Celsius and a CPU at 71 degrees.

Temperatures on the GPU were flat out unacceptable for long term usage while the CPU was in a reasonable range. Results would vary depending on the case you use, but both temperatures were 20-30 degrees higher than what you would expect in a fully cooled case. PC and server cases work similarly, with the exception of additional additional “cooling shrouds” on servers.

For servers, heat management is even more important because they run 24/7, are in thin chassis and have more components. Intel CPUs have a maximum heat capacity of 100 degrees celsius and once that is reached, the CPU decreases voltage and clock speed, dramatically impacting performance. If it is unable to control temperatures after throttling, the system will crash.

Having a well ventilated server could make the difference between a safe operating temperature and decreased performance or complete failure. Server Case UK recommends a 4U Rackmount chassis for best cooling as you are able to move large volumes of air with a 140mm fan. Not everyone needs this much cooling, and mainstream brands like Dell, IBM and HP can be trusted to properly manage thermals in a thinner chassis. 

Controlling a server’s environment 

The most notable difference between consumer PC and server thermal management is that people usually have more than one server. As you increase the amount of servers in use, their environment becomes more and more important. If you have a bunch of servers, you’ll need to put as much effort into cooling the room as you do cooling the case. 

Data centers and server rooms will have different cooling mechanisms, but the general idea is the same. Cold air goes into the front of the server and hot air is exhausted out of the back. Your focus is to make sure that hot air doesn’t leak into an area where cool air is coming from. 

Products to improve server airflow

There aren’t any cooling accessories you can add inside of a server chassis that the OEM didn’t supply. Thankfully, there are some tools that can definitely improve thermal performance when rack mounted. 

1. If your rack has any open space, there is risk of hot air recycling into the cold air section. Blanking panels help prevent this by giving hot air less access to the front of servers.
2. Even if you use blanking panels, stagnant air can create hot spots. These develop after long use in a poorly ventilated area and can increase temperature of equipment around it. Installing server rack fans can help move around the heat in an area with hot spots. 
3. A combination of a blanking panel and rack fan tray is a horizontal rack fan. These are able to seal off airflow and break up hot air in the rack. 
4. Lastly, an effective measure to direct airflow is to put side panels on an open frame rack. This is another way to stop cold and warm air from mixing and to help control temperature.