DATA CENTER TYPOLOGIES

The major concern for data centers is to ensure the continuity of energy supply and improve the energy efficiency. The tier systems with different typologies contribute to improve the reliability and availability. The comparison of AC and DC energy distribution in the data center gives some guidance on the electrical configuration design.

A. Tier Classifications

             The Uptime Institute defines four tier system typologies for describing the availability of system as shown in the Figure 1. It can be seen that the difference between Tier I and Tier II is the number of generator and UPS. In Tier II, additional generators and UPS provide backup for the most critical components. The significant difference between Tier II and Tier III is the number of delivery path. In Tier III, the alternative power from a second utility provides the parallel power support for the critical IT load, in case of power failure of the primary path. However, there is no requirement to install UPS in the passive path. Therefore, Tier III system is vulnerable to utility conditions. Tier IV provides a complete redundant system by adding two active power delivery paths. It can enable dual systems to run actively in parallel. In both power paths, it contains N+1 UPS and generator sets. The comparison of performance in different Tier systems is shown in Table II. It shows that higher level of Tier system has greater system availability

Figure 1. Typologies of different Tier systems.

Table 1. Comparison of Tier systems

 B. AC and DC Energy Distribution in Data Centers 

              Typically the discussion of AC versus DC in the data center starts with efficiency. Since a data center draws a significant amount of power, a relatively small increase in efficiency can lead to a reduction in operating costs. The advantages of DC data center over AC are energy efficiency, reliability, smaller carbon footprint, lower installation and maintenance costs, scale ability, easier integration of renewable energy, utility rebates and credits, and safety. Total energy savings can reach upward of 30% for both mechanical and electrical power savings. Because of this efficiency, DC systems can use various utility rebates and credits available for corporations. There are fewer power components in a DC system, making it more reliable than an AC system. With fewer power conversions, there is also less heat to affect the electronic equipment. It is because every conversion wastes energy and produces heat. And while any single conversion may be in the mid 90 percent range, they don’t add together, they multiply. When energy to remove the heat is considered, it is only about 50% of the energy that actually gets used by the processors in the servers.