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Data centers require tight coordination between the trades, special consideration for redundancy and reliability, and carefully scripted commissioning of systems. Consider, for example, the issue of redundancy. For non-critical commercial facilities, the design for redundancy typically is approached on an equipment basis. For example, in a chilled water plant with a 1,000 ton (3517 kW) load, three 500 ton (1760 kW) chillers may be provided to meet the requirement of N+1 redundancy. With this design, in theory, any chiller can be pulled out of service and the plant can continue to serve the design load. With an office building, this simplistic view of redundancy may be sufficient. Failure to meet the design load merely causes an inconvenience to tenants; it does not compromise the core business.
With data centers and other mission critical facilities, engineers are challenged to think in terms of system failures, and more sophisticated techniques are required to analyze critical links. In our previous example, consider the failure of an electrical panel that serves two or all three of the chillers. Although the chillers were designed for N+1 redundancy, a failure of the electrical feed to more than one chiller can shut down the data center.
As compared to the office building, the risk of failure in data centers is compounded by several issues: 1) with high density loads, the time for recovery from equipment or system failure is much shorter; 2) the cost of failure is much higher; and, 3 ) as loads may cluster within any group of racks, redundancy must be provided in the "downstream" distribution system as well as the central plant.
This article presents a process that can be used to review and test the system design to achieve a high degree of system reliability. It also emphasizes the importance of close coordination required in the design of the electrical, mechanical and control systems and summarizes the experience of two firms (one mechanical and one electrical) that have collaborated in the design and commissioning of many data centers.
A Commissioning Process
This article cannot comprehensively cover all of the steps in commissioning a data center, but it highlights the four key steps and provides examples from real projects for each. These steps are:
* Design review;
*...