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Hot Aisle or Cold Aisle Containment

Hot Aisle:

More Efficient

More Expensive

Area around servers is cool

Hot aisle is very uncomfortable

Easier for new data centers

A common practice in the modern data center is aisle containment. Containment refers to a system that encloses a space in between servers.

There are two types of containment: hot aisle and cold aisle.

On the right, you can see an illustration of hot aisle containment. In a hot aisle containment system the room in filled with cold air and the servers take advantage of that for cooling. The air is heated as it goes through the servers. In order to prevent the hot air from killing hard drives or other equipment, it is contained in the center. It can then be dealt with in a variety of ways. One way is by having air handlers directly above the containment system. This is one of the ways we can do it inside of our Critical Infrastructure Module. Another popular method is what is known as in-row cooling. In this system, heat is contained in the center and is exhausted through chillers that are in line with the servers. The room around the servers warms up and is chilled by either rooftop units, through wall CRAC units or a central AC plant.

Cold aisle containment is the exact opposite.

Instead of containing the heat hot air coming from the servers you instead create a small area to cool. These are usually connected to CRAC cooling units in the computer room but can be connected to rooftop units or a central AC plant. In-row cooling is not really an option due to the small area the both the hot and cold air would be coming from. Cold aisle containment is usually used when retrofitting an older data center as it is cheaper to implement. In our data modules, both hot and cold aisle are available and they have the same cost, so it is up to you to determine what is best for your needs.


There are many ways to cool a data center beyond these, however containment systems have relatively low additional costs and can save a lot of energy. They usually have a payback period of 1-2 years.


Due to the way our modules work, cold aisle containment is more efficient. A normal data center would see higher efficiency with hot aisle containment because of the workspace around the servers would need to be cooled for the worker's comfort. In our modules, there should be no workers permanently stationed and the area that needs to be cooled is much smaller, reducing cooling needs. That being said, hot aisle containment is not without merit. Having a pressurized cold room allows for the more effective use of a vestibule as dust and dirt and pushed out of the server room via air pressure. ​

Based on Traditional Data Center

Cold Aisle:

Less Efficient

More Affordable

Area around servers is hot

Cold aisle is comfortable

Easier for old data cneters

So what is the best option?

In order to answer that, we must look at why server rooms are cooled to 75 Fahrenheit. Modern CPUs, RAM and motherboard components can operate up to 95 Celcius, that's about 200 °F, this is why "hot water cooling" works. Even 140F water in Arizona can cool a CPU. Solid State Drives can operate from 60-75 °C or 140-165 °F and about the same for networking equipment. The ONLY reason the hardware is cooled to 75 °F is because of hard disk drives. If it were not for hard drives, data centers could operate at much higher temperatures. These temperatures would also be too hot for workers, so they would likely be brought down a bit. Because of hard drives, sub-ambient temperatures must be reached (although free-cooling can be taken advantage of) and this requires enormous amounts of energy. These costs can add up and choosing a sub-optimal cooling solution could change your electricity costs from 10% of the server costs to 40%.

Now that we know why we need to cool things down we can determine what is the best. So, we want to operate at the highest possible temperature without killing hard drives. We also have to factor in human workers. Even in our modules, people will still need to go in and maintain equipment. People produce heat and will disrupt thermal equilibrium. We need to be able to account for that temporary extra heat. Cold aisle is more efficient in our modules and hot aisle is more efficient in a traditional data center. Hot aisle systems have a greater heat capacity as there is a larger room full of cold air to absorb extra heat. However, enterprise hard drives can safely operate 24/7 at up to 85 °F so by operating at 75 °F you should have enough heat capacity to account for latent heat. 

With all that said, hot aisle is our choice for a traditional data center and cold aisle is our choice for a modular data center.

If you are interested in either hot or cold aisle containment or are wondering if a different system would work for your unique needs, please contact us so we can help you evaluate your needs.

If you have questions or would like some more information, please contact us.

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