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Part 2: UPS Design Concerns: Cooling, Surge Protection, Maintenance and Batteries
By John Yoon
February 2014 -
There are a number of design concerns to keep in mind for a UPS. Cooling, surge protection, maintenance, and batteries all must be incorporated into a comprehensive UPS design.
3. Design for adequate cooling. Designing adequate cooling for the UPS room will ensure the reliability of the equipment itself. While UPS equipment can tolerate relatively high temperatures for short periods of time (typically up to 104 F), most manufacturers recommend a temperature of 77 F or less for this room. A rule of thumb: For every 10 degrees Celsius (18 degrees Fahrenheit) increase in operating temperature, the expected life of the UPS components can be cut in half. Redundancy applies to the air conditioning for the UPS room as well. If only a single air conditioning unit supports the UPS room, what happens if it fails or needs to be shut down for maintenance?
4. Don't forget SPDs. While the UPS protects the downstream load in the event of a power failure, the UPS itself should be protected via a surge protective device (SPD). Power semiconductors used in modern UPS design still are sensitive to transient overvoltages caused by lightning, utility grid switching, etc. While the UPS may have some form of integrated SPD, an external SPD provides additional insurance in locations with power quality issues.
5. Proper UPS location for security and maintenance. The best location for a UPS is based on the pessimistic assumption that it will fail and the most likely cause for that failure will be human error. As such, the location should limit access and be designed such that in the event of a catastrophic failure, required replacement parts can be moved in and out with ease. (Remember: Many larger UPS units cannot fit through a standard 3-ft. door opening.)
6. UPS batteries. Aside from human error, battery failures are the most common cause of UPS downtime. Because battery issues often go undetected until batteries are needed, monitoring the health of the batteries can be the first step to avoiding a potential failure. A battery monitoring system can be added on to the battery strings to compare the UPS battery characteristics over time to predict when they will fail.Typically, VRLA (valve-regulated, lead-acid )batteries carry a 10-year prorated warranty, but it is accepted industry practice to proactively replace them after just five years.
The quantity of batteries for each UPS system is directly proportional to the load and amount of run time required. But the more batteries needed, the more potential points of failure exist, as it only takes one battery failure to bring down an entire UPS system.
7. Monitoring. Because the UPS system is typically housed in a back-of-house location, remote monitoring is a must. Regardless of when a failure happens, facility staff must be informed immediately that something has failed. Specify the UPS with optional network interface cards that can accomplish this via e-mail or SMS notification.
Part 1: UPS's Key Role In Data Centers Demands Close Attention To Preventing Problems
Part 3: Commission UPS Before Operations Begin To Ensure Performance Meets Expectations
Part 4: Tips For Operating UPS In Data Centers