Consulting-Specifying Engineer - May 2008 - (Page 79) Equipment Lifecycles Selecting, maintaining UPS Power protection is critical to any organization’s power infrastructure. Users enjoy a long-term power solution after selecting the correct UPS and then correctly maintaining it. BY ED SPEARS, Product and Training Manager, Eaton Corp., Raleigh, N.C. E ngineers who design and specify systems should be cognizant of the various conditions that facilitate optimal lifecycle performance for an uninterruptible power supply (UPS) system. Among the factors to consider: selecting a UPS uniquely suited to a particular customer and the facility; ensuring that environmental concerns are addressed; overseeing the system’s integration with control systems; and outlining appropriate service requirements for ongoing UPS health. Because today’s MEP designers face a variety of integration issues, it can be beneficial to consider a power chain offering, in which a single vendor packages an integrated system to include products such as surge suppression devices, switchgear, HVAC, power distribution, equipment racks, and generators. In addition to providing significant savings for a customer, a packaged solution also offers a more coordinated approach that is easier to maintain. The up-front capital cost also may be lower. When specifying a UPS, attention must be paid to right-sizing and load matching requirements. Typical guidelines recommend that a UPS be loaded to no more than 80% of its rated capacity, which primarily is to allow headroom for unplanned additional loads. In parallel systems and dual-bus architectures, the UPS system often will operate at less than 50% of load, oftentimes at about 40%. If the system is a 2N+1 configuration, the system can be at 100 86 80 Load losses by unit 60 56 40 23 20 5 0 0 1 2 3 Number of preventive maintenance visits 6 4+ Figure 1: UPS load losses decrease as the number of preventive maintenance visits increases. Source: Eaton Corp. Consulting-Specifying Engineer • MAY 2008 79
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