Guidelines for energy-efficient datacenters

Energy costs and consumption
For years, electrical power usage was not considereda key design criteria for datacenters. Nor was electrical consumption effectively managed as an expense. In fact, many datacenter managers are unaware of what their monthly energy bill is. This is true despite the fact that the electrical energy costs over the life of a datacenter may exceed the costs of the electrical power system including the uninterruptible power supplies (UPS), or even exceed the cost of the IT equipment itself. The reasons for this situation are as follows:

• Electrical bills are sent out long after charges are incurred. No clear link exists between particular decisions, like the installation of a new zone of equipment in the data center or operational practices and the increased cost of the electricity. In fact, electrical bills are viewed as an inevitable event that most people don't consider trying to influence.
• Tools for modeling the electrical costs of datacenters are not widely available and are not commonly used during datacenter design.
• Billed electrical costs are often not within the responsibility or budget of the datacenter operating group.
• The electrical bill for the datacenter may be included within a larger electrical bill and may not be available separately.
• Decision-makers are not given sufficient information during planning and purchasing decisions regarding the energy cost consequences.

Figure 1: Where Does It Go?

System design issues that commonly reduce the efficiency of datacenters include:

• Power distribution units and/or transformers operating well below their full load capacities.
• Air conditioners forced to consume extra power to drive air at high pressures over long distances.
• Cooling pumps which have their flow rate automatically adjusted by valves (which dramatically reduces the pump efficiency).
• N+1 or 2N redundant designs, which result in underutilization of components.
• The tradition of oversizing a UPS to avoid operating near its capacity limit.
• The decreased efficiency of UPS equipment when run at low loads.
• Under-floor blockages that contribute to inefficiency by forcing cooling devices to work harder to accommodate existing load heat removal requirements. (This can lead to temperature differences and high-heat load areas might receive inadequate cooling).