Managing Energy Costs in Data Centers

Data Centers

Data centers are notorious for their intensive energy consumption. According to the US Department of Commerce, these facilities can have power densities nearly 40 times higher than those of commercial office buildings, but those power densities vary significantly from one data center to the next. Because large, concentrated power usage is expensive and burdens the electrical grid, data centers are excellent targets for efficiency improvements. The first loads to evaluate in any load-reduction effort are the server and HVAC systems; they are the primary energy consumers in the data center (Figure 1). And they can offer simple payback periods of a few years or less.

Average energy use data

Figure 1: Energy consumption by end use
Because energy-use data for large data centers is relatively hard to come by, a representative average has not been established for this sector. These charts represent energy-use data for 13 facilities (A, B), only 3 of which are dedicated data centers, meaning that they have no other business operations (C, D). Based on this small data sample, it appears electricity consumption in dedicated facilities is led by lighting and the requirement of ventilation. For both dedicated and non-dedicated facilities, space heating is the primary use for natural gas.
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An efficiency-improvement program should first target the IT power load because savings can be realized with little or no cost and are amplified through the reduction of cooling loads. All of the power used by IT equipment eventually turns to heat, which the cooling system must then remove. Therefore, if the IT equipment uses less energy, the accompanying reduction in the facility’s cooling load will lead to additional energy savings. Although there is considerable variation among facilities, a typical data center that reduces its computer load power requirements by 1.0 kilowatt (kW) would also offset approximately 0.6 kW of air-conditioning power (Figure 2).

Figure 2: Savings in IT energy use lead to significant upstream savings
Although the main purpose of a data center is to operate IT equipment, in this example, 47 percent of the total power entering the data center directly powers the servers and chips. Within each server, an even smaller fraction of energy is actually used to provide valuable computing services.
Savings in IT energy use lead to significant upstream savings

Efforts to reduce the baseline consumption of data centers tend to be effective because data centers typically exhibit high load factors, with little distinction between baseline and peak demand. This high load factor has two causes: First, data centers almost always operate 24 hours a day, year-round, so there is little relief during what would normally be off-peak hours or seasons in other industries. Second, most servers in data centers typically draw a large fraction of their peak demand even when lightly loaded or running idle (Figure 3).

Figure 3: Data centers show a high load factor
In large data centers where operators increasingly turn to server virtualization, along with other means of maximizing the servers’ computational capacity factor and improving auxiliary system efficiencies, electricity demand profiles are very flat.
Data centers show a high load factor

Lawrence Berkeley National Laboratory (LBNL) estimates that, by implementing aggressive load-management strategies, the typical data center could save between 20 and 40 percent of its annual energy costs. Savings of up to 50 percent are even possible.

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