Implementing Energy Efficient Data Centers

Overview

The paper first measures the value of a watt. At $0.12/kWh, 1 kW of continuous IT load costs about $1,000 a year and about $10,000 over a 10-year life; including infrastructure losses it roughly doubles to about $20,000. As an example, a 200 kW data center has about $4M of electricity cost over 10 years. Once capacity, capex and opex effects are included, the lifetime value of saving 1 kW of IT load is about $43k, against about $10.6k for energy alone.

On efficiency, a typical 2N data center at about 30% load delivers only about 47% of its input to IT. The measures recommended are consolidation and virtualization, efficient server platforms, right-sizing, row-oriented cooling, economizers and efficient UPS. Efficient server form factors cut IT power about 20%; consolidation and virtualization do dramatically more. Here efficiency means the fraction of input power that reaches the IT load.

Systematic programs can cut the electric bill 20 to 50%, and up to 90% in extreme cases. The author argues consumption is roughly split between IT and infrastructure, so the two must be designed as one system. The paper dates from 2011, so tariffs and equipment efficiencies belong to that period; the logic (capacity cost exceeding energy cost, efficiency loss at low load) still holds for design decisions.

Key points

1. At $0.12/kWh, 1 kW of continuous IT load costs about $1,000/yr, about $10,000 over 10 years, and about $20,000 with infrastructure losses.
2. A 200 kW data center has about $4M of electricity cost over 10 years.
3. A typical 2N data center at about 30% load is only about 47% efficient.
4. Lifetime value of saving 1 kW of IT load is about $43k with capacity, capex and opex effects, versus about $10.6k for energy alone.
5. Systematic programs can cut the electric bill 20 to 50%, up to 90% in extreme cases.
6. Efficient server form factors cut IT power about 20%.

Using it in design

• Expose a 'value of a kW' widget: lifetime cost = 8.76 MWh/yr x tariff x PUE x life (default $0.12/kWh, 10 years) plus a capacity-cost term.
• Evaluate the efficiency model at the expected real load fraction (e.g. 30%), not nameplate, because 2N systems at low load are inefficient.
• Use this value in TCO comparisons and to justify efficiency options.

Who should read it

Designers, finance and operations decision makers looking for a business case for efficiency spending.

Related standards

• ISO/IEC 30134-2
• EU Code of Conduct for Data Centres

Publication details

Authors

Neil Rasmussen

Publisher

Schneider Electric

Year

2011

Document number

WP 114

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation