Maximization of energy efficiencies in existing and next generation data centers has been a trend in the IT industry. For several years, the focus has been on how to maximize HVAC systems with little or no impact on the electrical systems, which have remained untouched partially due to the "black box" concept. With electrical distribution changing little in over a century, designing an efficient electrical system is very challenging due to the limitations of industry infrastructure. However, there are options available to maximize your electrical system that can provide significant payback. The manufacturing industry has made significant advancements in technology that can be applied to many data centers, though choosing the best technology and options available from a myriad of items can be a challenge.
Most losses in a data center's electrical distribution system occur between the Uninterruptible Power Supply (UPS) and the utilization equipment (such as a server). In order to evaluate the various options available, a basic understanding of the level of reliability should be discussed. Although many versions of tier structure reliability are presented by various entities in the industry, the basic concept is common.
The major components that impact electrical system losses are the electrical equipment (such as UPS, Power Distribution Units [PDUs]), the infrastructure distribution (wire, breakers, bus, etc), system and component redundancy, and distribution voltage. Traditional voltage distribution in most commercial buildings is 480/277V, with localized step down transformation to a 208/120 volt system. A commercial building operating at 480V maximizes the efficiency of utilization equipment for commercial buildings (such lighting, motors, etc).The utilization voltage transformation is simple and provides the greatest flexibility. However, data centers are not your typical commercial buildings. The machines that operate in the data center require high density power and cooling. The unique and large power demands require the users to evaluate the optimal voltage for the facility. Three alternate configurations to consider are 600V, 400V, and traditional 480V systems as the input and output of UPS.
The 600/575V system maximizes the use of higher voltage to reduce current, thus decreasing I^2R losses and maximizing the infrastructure capacity by increasing the voltage and decreasing the current. This system allows the total power available for constant switchgear bus rating to be increased. Configuration requires transformation from 600V to 208-240/120V at the utilization voltage to the rack. This system requires service transformers to provide 600V to the input of the UPS and produce 600V on the output of the UPS for distribution to the raised floor. At the raised floor, local transformer panelboards (such as PDUs) step the voltage down to either a 240V or a 208V system. Although there are efficiency gains by utilizing the higher voltage, a major advantage is to use a 600V system to increase the system capacity and to maximize the infrastructure ratings.
The most widely used distribution for a data center is the 480V system. Since this is the predominant voltage in the United States, equipment for 480V is more readily available. A 480V service provides input power to the UPS and the output is at 480V for distribution to transformers and panelboards. The transformers step the voltage down from 480V to 208-240 /120V for utilization equipment. The UPS equipment is designed to maximize efficiency for 480V systems at full load; though at part load efficiency is getting new attention and a closer look. The 480V output from the UPS is distributed to local transformers and panelboards to step the voltage down to 208-240/120 V to the raised floor. Although the efficiency of the UPS is higher, the overall system efficiency is lower because of the mismatch of voltage with the utilization equipment and transformation losses of the system.
A 400V system is widely used in Europe and utilizes 400V input to the UPS and distributes at 400V at the output to the raised floor. Since 400V phase-to-phase will produce 230V phase-to-ground, there is not transformation to step down the voltage to the utilization equipment. Most power supplies on the raised floor can operate up to 250VAC thus 230V may be directly utilized. Distribution panelboards can be provided without transformers to the load. As with a 600V system, the module efficiency for the 400V is not as high as the traditional 480V system; the overall system efficiency can be higher, especially at part load, since there are no transformation losses.
In selecting the best voltage to the raised floor, the system as a whole should be evaluated. Some key factors to evaluate are part-load efficiencies, capacity, and redundancy. In addition, it is important to evaluate the maximum capacity available with off-the-shelf standard products. Assuming the limitations of an input bus of 5000 amperes, recharge current, and efficiency of the modules, an approximate maximum capacity of various voltages can be extrapolated.
To apply the best voltage for a data center, several factors must be taken into account. Some of the primary factors beyond the efficiency of the system should be evaluated with consideration given to how the selected voltage will affect your facility:
- Maintainability - Ability for the staff and/or manufacturers to properly maintain the infrastructure.
- Operational - Consideration in understanding the system limitations in normal and failure modes and impact of the life of the equipment.
- Reliability - Risks both manufactured equipment and operations.
- Cost (first cost and operational) - The initial cost of implementing the system relative to the market and cost of operation/maintenance for the life of the facility.
To select the optimal voltage to the facility, the decision cannot be made in a vacuum. The best solutions are based on the system redundancy and capacity configuration for the modular approach in planning and designing your data center.
About RTKL
RTKL Associates Inc. is one of the largest multi-disciplinary design firms in the world. Headquartered in Baltimore, Maryland, the firm boasts a staff of more than 1,100 professionals strategically placed in offices in Chicago, Dallas, London, Los Angeles, Madrid, Miami, Shanghai, Tokyo and Washington, DC.
RTKL offers a comprehensive continuum of creative services including planning, architecture, interior architecture, M/E/P and structural engineering, telecommunications, security and audiovisual design, environmental graphic design, and landscape architecture. Among the firm's portfolio are corporate, academic, commercial, mixed-use, retail, government, hospitality, entertainment, health and science, and transportation projects.
Adapted from a White Paper by RTKL
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