Frequently asked questions
1) What kind of cabling infrastructure should be in my data center and why?  
This really depends on several factors. First and foremost is the length of time you plan on being in that facility. Obviously, short term data centers may be different than longer term facilities.

Broadly speaking, your options are single- or multimode fiber only (which is quite rare), a combination of fiber and copper (the most common) or copper only. Fiber will likely remain the medium of choice for backbone applications. Your choice in fiber is either 62.5 or 50 micron multimode in various grades (internationally also OM3) with the most popular being 50 micron laser optimized or you may also hear the term zero water peak. Some facilities build in an amount of single mode for future proofing, but it will likely remain dark for some time.

On the copper side, your choices are category 6, 6A (shielded or unshielded) and category 7/class F (fully shielded S/FTP). As of today's date, category 7/class F is the only published standard that is called out in the IEEE 802.3an standard for 10GBASE-T. The category 6A (augmented category 6) standards should publish in 2007. Category 7A standards are also in progress although products for that standard are already available. Basically a 7A system is a 7 system with 1000MHz cable.

2) How do I measure the cooling consumption of my data center?  
Cooling consumption cannot accurately be measured in the data center. However, there are a few strategies that will help you approximate how much cooling your data center is consuming.

You can monitor and record power consumption. This is the major variable that correlates to cooling requirements. Get as accurate and precise as possible - right down to individual cabinet power strips, which are now available with both local and remote metering. This will also help you maintain load balance on dual UPS's and phase balance on 3-phase circuits, both of which contribute significantly to power stability.

Install temperature and humidity monitors at key locations in the room. Preferably, install monitors in each cabinet, too, but at least in each "High-Density" cabinet. There are many systems now available to do this. The system won't tell you how much cooling you need, but this will certainly identify when and where cooling is needed.

3) What is the minimum ceiling height of a data center?  
At least 12 feet . . . but 14 feet is even better. Generally speaking, the higher you can go the better. The space above the cabinets accumulates rising heat, which minimizes its mixing with cold air. This improves air conditioning efficiency. Obviously, it also provides space for overhead cable trays and good lighting.

4) How should I use vapor barriers in the data centers?  
The purpose of a vapor barrier is to keep condensation out of insulation because moisture reduces the insulating value. They also keep moisture from ultimately rotting the insides of walls. If the walls don't go from floor to the slab above, this is not a concern since moisture can escape out of the open walls at the top. But a data center wall should be slab-to-slab, both to maintain the interior environment and to provide the fire rating. The generally accepted rule is that the vapor barrier goes on the warmer side of the wall.

5) What best practices should we follow for normal operation during a UPS maintenance window?  
During UPS maintenance, companies providing mobile power have to service a variety of customers and usually use very good, well regulated equipment. The main thing I would suggest is that your Power Feeder is protected with a good Transient Voltage Surge Suppressor (TVSS).

6) How do I figure size requirements for new UPS unit?  
For years, large UPS systems have been designed based on a PF of 0.8, which means that a 100 kVA UPS will only support 80 kW of "real" power load. Most UPS systems continue to be designed that way, even though the majority of technology today has power factors of 0.95 – 0.98.

Neither the kW nor the kVA capacity of the UPS can be exceeded, but because of the higher PF numbers, it is usually the kW rating that governs today. There are, however, some UPS systems on the market that are PF-corrected so that the kW and kVA ratings are the same.
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