Efficient Data Center:
Electricity usage costs have become an increasing fraction of the total cost of ownership (TCO) for data centers. It is possible to dramatically reduce the electrical consumption of typical data centers through appropriate design of the network-critical physical infrastructure and through the design of the IT architecture. This paper explains how to quantify the electricity savings for data centers and provides examples of methods that can greatly reduce electrical power consumption.
Electrical power usage is not a typical design criterion for data centers efficiency, nor is it effectively managed as an expense for data centers. This is true despite the fact that the electrical power costs over the life of a data center may exceed the costs of the electrical power system including the UPS, and also may exceed the cost of the IT equipment. The reasons for this situation are as follows:
- The billed electrical costs come after the charges are incurred and are not clearly linked to any particular decisions or operating practices. Therefore they are viewed as inevitable.
- Tools for modeling the electrical costs of data centers are not widely available and are not commonly used during data center design.
- The billed electrical costs are often not within the responsibility or budget of the data center operating group.
- The electrical bill for the data center may be included within a larger electrical bill and may not be available separately. - Decision makers are not provided sufficient information during planning and purchasing decisions regarding the electrical cost consequences.
This paper will show that energy efficient data centers all of the above can and should be corrected, because substantial financial savings are possible for typical users. The greatest advantage can be gained in the design of new facilities for data center efficiency, but some savings are possible for existing and evolving facilities as well. Simple no-cost decisions made in the design of a new data center can result in savings of 20- 50% of the electrical bill, and with systematic effort up to 90% of the electrical bill can be avoided.
What is the cost of electrical power consumption: Data Center Efficiency
A typical value for the cost of electrical power is $0.12 per kW hr. Given this cost, the annual electrical cost per kW of IT load is approximately $1,000. Over the 10 year life of a typical data center this translates to approximately $10,000 per kW of load.
As a general rule, approximately half of the energy used in a data center goes to the IT loads. The other half goes to the network-critical physical infrastructure (NCPI) equipment including power equipment. This means that for each kW of IT load the 10 year electricity cost is approximately $20,000. For example, a 200 kW data center would have a 10 year electricity cost of $4,000,000. This is a material cost for any organization and all IT professionals should understand where this expense is going and that it is avoidable.
Data Center Efficiency Solutions:
Approximately half or less of the energy used in a data center goes to the IT loads. The other half goes to the network-critical physical infrastructure (NCPI) equipment including power equipment, cooling equipment, and lighting. Figure 1 shows the electrical power flow in a typical high availability data center. Note that all the energy consumed by the data center ends up as waste heat which is rejected outdoors into the atmosphere caused decreased data center efficiency. Figure 1 is based on a typical data center with 2N power and N+1 cooling equipment, operating at approximately 30% of rated capacity.
Efficient Data Center is a poor metric
Many discussions regarding electrical power consumption use the term "efficiency". While the underlying meaning of terms like "improving efficiency" are well understood, the technical use of the term "efficiency" for quantitative assessment of data centers leads to confusion. Discussions are much clearer when electrical power consumption (kW) is the metric used, rather than efficiency metrics. For example, if two different devices in (data centered efficiency) a 50% and 80% efficient, it is not clear how to combine their efficiencies into a single number that relates to costs. In fact, the electrical costs would actually be dependent on the quantity of power flowing through each device. Furthermore, some devices like computers or lighting are zero percent efficient which is a confusing concept and conveys no quantitative information regarding their electrical use.
