Ben Hatton How Data Centers use Hot/Cold air Separation to be Energy Efficient

September 9, 2013 by · Leave a Comment 

One topic that continually comes up in the world of data centers is energy efficiency, and what data centers can do to help trim their overall energy use and reduce their carbon footprint.

datacave_exteriorAccording to the US Department of Energy, up to 1.5% of all electricity in the entire country is used specifically to power data centers (for more specifics, check this out). That is a staggering number when you think about it! This number will only go up as well, as more and more business and personal data is created and managed within data centers.

Data centers have traditionally been demanding when it comes to energy use (the above statistic is a testament to that), and will always require a huge amount of energy to operate. However, there are methods that some data centers (and the clients using them) can use to help improve their overall energy efficiency. A few upcoming blog posts will examine some of these methods in depth, but we will start with the single most critical component to any data center: its cooling system.

Traditional Cooling Method

Keeping client equipment cool is always a top priority for any data center, so a huge percentage of the energy used in the data center is specifically for cooling. Traditionally, data centers would utilize raised floors as well as overhead AC units to keep racks cool. While it was certainly a good starting point for the industry, in recent years that methodology has proven to not be very cost-effective for the data center provider, or the clients themselves. Also, as more and more client servers are added to each rack (more servers=more heat), this method can easily result in “hotspots” popping up in each rack, creating a danger to the machines running in the data center.

The reason for this all has to do with the air flow: the traditional approach didn’t allow for much actual SEPARATION between the cold air being put out by the CRAC (computer room air conditioner) and the hot air being put off by the equipment being stored. This can lead to inconsistencies in the temperature itself, as well as in the distribution of temperature across the data center. In an environment where 100% uptime is expected of your equipment, even small variations of temperature like this have the potential to lead to disastrous consequences, such as what occurred with several of Microsoft’s services earlier in the year.

Hot-aisle and Cold-aisle Separation

Because of this risk, the approach we take at Data Cave for keeping client equipment cool is by utilizing “hot-aisle separation.” At its core, this approach involves isolating the heat that is generated by the servers, so that it is not mixed with the cold air being put out by the CRAC units. When the hot air is separated from the cold air in this manner, the overall efficiency of the cooling process is improved, and energy costs are also reduced as well.

Dome data centers have expanded on this concept even further by utilizing methods known as “hot-aisle containment” and “cold-aisle containment.” These take the separation of hot and cold air to the next level, by physically blocking off the cold and hot aisles. While we don’t currently utilize this approach at Data Cave, moving to a “containment” approach is something that could be done in the future.

There are multiple ways that these containment methods can be implemented within a data center, but here is how each method works:

Cold-aisle Containment: The areas directly in front of each server rack are segmented off from the rest of the space in the data suite, and all of the actual cooling takes place in this area ONLY. This ensures that the server intakes in each rack are always receiving cold air from the CRAC’s, on a consistent basis. The fact that the hot and cold air are kept separate allows for this consistency. The photo to the right shows an example of this method, where the cold aisle is physically separated from the rest of the space in the data center.cold_aisle

Hot-aisle Containment: On the other side of the racks, the back rows are completely separated from the rest of the data suite as well, allowing for all of the hot air generated by the servers to be in the same location (totally separate from the cold air on the front side of the racks). From here it becomes much more straightforward for the hot air to be pulled in through the AC intake, where it can then be cooled.

Whether or not a data center employs a full containment method for the hot and cold air near the server racks, taking measures to separate the hot air from the cold air is definitely the preferred approach when it comes to keeping client equipment consistently cool. In addition to being a solid cooling method for our clients’ equipment here at Data Cave, it’s also better for the environment because it allows for consistency in the amount of cold air that needs to be put out by each CRAC. This ultimately makes the energy needed for cooling very predictable, and inevitably, lower.

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