Читать книгу Maintaining Mission Critical Systems in a 24/7 Environment - Peter M. Curtis - Страница 59

Suppose we made only one conversion of the incoming AC to DC at the UPS, and then distributed the DC throughout the facility without any further conversions, thereby eliminating two power conversions along with the attendant losses. Not only would this make for a more efficient system, it would also reduce the number of components, thereby eliminating points of failure, making for a more reliable system. As an example, a 380VDC distribution system will result in a 200% increase in reliability, a 33% reduction in required floor space and a 28% improvement in efficiency over conventional UPS Systems, or a 9% improvement over ‘best in class’ AC UPS architectures. A DC distribution system would also facilitate the integration of on‐site DC‐generating power sources, such as solar PV arrays, wind power, and fuel cells, which all can provide DC power without a single power conversion. For example, the best published efficiency for a fuel cell is 50%. According to UTC Power, by eliminating the AC power conditioning subassembly and utilizing waste heat in a combined cooling, heating, and power application, efficiencies can exceed 85% with a high load factor.

Figure 3.4 below shows the various power conversions that are required in a conventional AC distribution system, along with those that are required to connect alternate energy sources.

Figure 3.4 Traditional AC Distribution

Figure 3.5 below shows the fewer conversions that are required with a DC distribution system and the simpler integration of alternate energy sources.

Figure 3.5 DC Distribution

This kind of DC distribution system can provide up to a 25% decrease in energy usage when compared to a traditional AC power distribution system by eliminating the losses associated with the inefficiencies of power conversion equipment. It also reduces the initial cost for electrical distribution equipment by about half. And since there are fewer conversions from AC to DC and DC to AC, which translates into less equipment, the distribution system occupies significantly less space. Proponents of DC power in data centers tout fewer single points of failure in DC systems due to the reduction in components. There is also the accompanying decrease in heat production. This reduces cooling capacity requirements and provides further reductions in operating costs.