Hot Aisle Containment (HAC) for Data Centers Explained

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Last Updated on October 4, 2022 by Josh Mahan

Looking for a way to reduce the energy expenses for your data center? According to Energy Star, data centers with hot/cold aisle arrangements can reduce their energy expenses by 5 to 10% by using containment systems. 

Employing hot aisle containment systems is a great way to moderate the temperature in data centers, protecting equipment and people while saving on energy costs. We’re looking at exactly what hot aisle containment is and how it may help your data center.

Related: Data Center Cooling 101: From Start To Finish

Hot Aisle Containment Explained

Hot aisle containment (HAC) is a method for improving the efficiency of a data center’s cooling system. The objective of an HAC system is to keep cold and hot air separate. By doing so, the entire process runs better. 

The system itself is mainly a physical separator placed around a data center’s hot aisle. The containment barrier helps to segregate cold and hot air while effectively directing them to different places, depending on where they are needed. This allows the cool air to move to the servers while the hot exhaust airflow moves back to the air conditioning return system.

HAC works similarly, yet in the opposite way as cold aisle containment. In a cold aisle containment system, the cold aisle is the one that is contained. This is based on similar properties related to heating and cooling, yet the execution is the opposite. 

Related: How to Cool a Server Room Properly [2022]

How HAC Systems Work

woman in hall next to server room

Hot aisle systems take advantage of the way air of different temperatures move. Most people know that hot air rises and that cold air sinks. Because of this, trapping and separating the cool and warm air isn’t too tricky. 

In most HAC systems, the hot aisle will be surrounded by a vertical partition that reaches from the server cabinets to the ceiling return. A duct system can be used if there is not a ceiling return. In either situation, the objective is to capture the warm air rising off the system. Then, this hot air can be directed to a specific point, which is typically to the ceiling return. 

Meanwhile, cooled air is pumped into the system through a separate pathway. This may be through ductwork, a raised floor, or AC units. No matter what method is used to pump this cold air, it is kept separate from the warm air. By not allowing the cold and hot air to mix, the air going into the AC is cooler; thus, your system does not have to work as hard to keep things cool.

So, once the complete system is constructed, it basically functions like a conveyor belt. Cold air enters the system, where it cools down the servers. In doing so, the cold air heats up and begins to rise. As it rises, it is carried out so that it does not heat up the servers. In many cases, this hot air is then fed back into an AC unit, where it turns into cold air, and the cycle begins again. The entire process is neat and orderly because it simply directs air where it naturally wants to go. 

Many systems also have an aisle containment door at both ends of the aisle. This allows the system to be accessed in case it needs maintenance, or anything needs to be changed. So, even though the system is relatively closed off, it is still accessible when it needs to be.

Want to learn more about how to keep a data center cool? Check out more of our cooling articles! 

Benefits of Hot Aisle Containment

Hot aisle containment has a few benefits in managing data center temperatures. The biggest one is that the supply and return airflows are separated. This means cold and hot air cannot mix.

This separation means conditioned air stays cool. There isn’t much chance it will heat up on the way back into the system. So, the air being added is cooler, which keeps the area cooler. Because of this, less cool air is needed when air is pumped into the area, and the AC does not have to work as hard. 

Meanwhile, exhaust air stays hot and dry. This is precisely the type of air that should be returned to air conditioning units. This is because AC units are at their most effective when taking in air like this. Return air that is hot with low humidity levels increases the cooling capacity of the entire system.

In fact, HAC can increase cooling efficiency by up to 30%. This has several benefits that add to the system. For one, an increase in efficiency leads to a reduction in the amount of energy needed. This directly leads to saving money on energy bills. Meanwhile, data systems remain at an optimal temperature. This allows them to continue functioning at their best. 

In addition to keeping equipment cool, the overall comfort of the center also improves. In cold aisle containment systems, the areas outside the cold aisle become much warmer. When this happens, it can reach the point where it’s uncomfortable for workers and possibly damaging to equipment. Meanwhile, HAC systems do not have this problem, so workers near the system will always be comfortable. 

Other grid systems can keep your data system at the correct temperatures. However, HAC systems tend to be easier and faster to install compared to these alternatives.

Related: Data Center Power: Best Guide to Efficient Power Management

Downsides of Hot Aisle Containment

Compared to cold aisle containment systems, hot aisle systems have a few downsides. The biggest is that they are generally more expensive. For smaller organizations, this could be initially prohibitive.

They also need ductwork to move the heated air. This can present a problem if the infrastructure is not currently there to support this air movement. 

However, we feel that even with these few downsides, HAC tends to be more beneficial for most situations compared to cold aisle containment or other grid systems. The benefits outweigh the additional costs that may come with a HAC system.

Need help planning your data center infrastructure? Learn more with Alertum’s resources!

Is Hot Aisle Containment Right for You?

telecommunication equipment

Hot aisle containment is an effective way to manage heat in data centers. While there is a higher upfront cost compared to the alternatives, HAC is vastly more efficient, saving energy and money over time.

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