Air containment can be a tricky subject, and knowing how much air containment is enough for a data center is a very common question. Schneider Electric has gotten this question so much that we decided to test containment across a range of “leakiness” to give some practical guidance. Continue reading to learn more about air containment and how to know how much is enough for your data center.
You have probably heard the term “percent leakage” as a way of assessing the effectiveness of a hot or cold aisle air containment solution, but you may not know what this actually means. One containment-related document defines percent leakage as the open area of a containment surface as a percent the total area. However, this definition leaves some questions unanswered. For example, you may ask if this includes the racks in the surface area or only the containment structure, or if this is with no IT equipment installed. The answers to these questions will significantly change the percent value.
Another document defines it as the amount of air that “leaks” as a percentage of air required by the IT equipment at a given pressure difference (deltaP) between the hot and cold aisle. In this context, “leak” means air that either bypasses the server or is oversupplied through the server. Both documents specify percent leakage values of no more than 3%, less than 5%, etc.
There are many variables when measuring percent leakage. When you finish your containment project and have to validate a percent leakage value, how would you practically validate that only 3% of the surface area was open and that only 5% of air was bypassing the servers? Also, the leakage flow rate is directly proportional to the number of racks, and you could use a different number of racks than what the specification assumed. The racks tend to be the leakiest element in a fully contained pod, so it’s important to remember not to install a containment that is significantly tighter than the racks.
Other variables that you may find in a production environment that complicate a percent leakage validation include IT equipment that has a different fan speed, racks from various vendors have different airflow characteristics, room shape that affects airflow patterns, and more. Practical metrics, including average temperature, the maximum temperature, and temperature variation of the IT supply air at the rack front should be used instead.
Finding the right temperature range is a key indicator for your containment project. The tighter you set your IT supply temperature range, the more containment you will need. A few factors that will help to establish this range include thermal runtime, cooling system redundancy, and ASHRAE upper limits.
Some people decide to set their IT supply air very low (around 65 degrees F), which allows them time to set up emergency cooling in case of a cooling system failure. This factor helps to establish the minimum IT supply air temperature. Be sure to check out Schneider Electric’s Data Center Temperature Rise Calculator to help you find your thermal runtime before you reach a max temperature.
If you have 2N cooling system redundancy, there is a high chance that you are willing to increase your minimum IT supply air temperature to close to the ASHRAE maximum recommended temperature (80 degrees F.)
ASHRAE upper limit is a good place to start for the upper limit of your temperature range- the maximum allowable is 89.6 degrees F for the A1 equipment class.
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