Wednesday, 8 August 2012

Planning for power (2)

In the previous blog entry on planning for power in a data centre I considered the need for a power budget and the need for a good change control process for variation in the power budget.
Most new data centres are initially only partially filled with equipment with space, facilities and resources left free for expansion. The power budget for the equipment expansion areas needs to be estimated in the early planning stages of the main construction project. It might be possible to postpone both capital and operational expenditure by fitting only the power infrastructure required at the moment, but in this case engineering space needs to designated and protected for future expansion. Additionally consideration needs to be given to the route through which electrical and mechanical plant will be moved during upgrades and maintenance.

When the power load has been established it will be possible complete the planning for air conditioning requirement.  The design of the air conditioning system will depend on what facilities exist for chilled water and what additional equipment can be installed within the building.

Consideration will needed on how long standby power will need to endure during a mains outage. This decision is not simply how long it takes for a standby generator takes to start and provide power. Consideration needs to be given as to how long it takes to gracefully shut down a data centre should the standby generators fail to start. An uncontrolled power crash can have devastating effects on ICT processing and the dependent businesses. The endurance requirements of the business will dictate how much energy needs to be stored in batteries. Consideration also needs to be given on how cooling will be provided if the generators fail to start. The required battery capacity affects the design of the battery room, but I'll cover that in a later blog article.

A joint decision will have to be taken, with the electrical engineer, on the power transfer switching arrangements will handover power to the standby arrangements and consequently back when Utility mains power is restored. For a data centre this switching is usually automatic with manual over-ride capability.

When the power requirement has been agreed, the engineers should establish the space requirements and weight of the air conditioning plant, machinery, transformers, switching gear, UPSs, generators, fuel tanks, batteries, ducting, piping and cabling  required. Agreement should be sought on where all of this equipment will be housed and mounted. The electrical equipment and air conditioning plant will impose an additional weight load on the building structure. The positioning of this weight/vibration load should be reviewed by a structural engineer to ensure the load is within the capacity of the building. Machinery such as generators, compressors and air handling units will create vibration in operation. This vibration might affect the building. The plans for damping and handling such vibrations should be reviewed by the building structural engineer.

Throughout the planning process it is highly likely that there will be obstacles to providing the equipment necessary to provide the power and cooling. For example there may not be enough space or the equipment is too heavy. In the worst case these obstructions may limit the amount of technology which could be deployed within a building. In any event there are likely to be many cycles of the planning process before an agreed solution can be achieved. Depending on the complexity of the data centre this process may take a few months. The process may involve agreement from the owners of the building and also regulatory planning authorities. If the original assumptions on power requirements change after the design has been settled it can be an expensive problem to fix.

Part of the planning process is to provide a solution which is affordable to the business client. It is in effect a process of risk assessment with the client where the proposed capital and operational costs are weighed against the risks and what the business can afford.

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