Retro-Commissioning Increases Data Center Efficiency at Low Cost: Success at Savannah River Site (FEMP bulletin, 2011)
U.S. DOE Federal Energy Management Program / Lawrence Berkeley National Laboratory · Geoffrey Bell
A US DOE FEMP bulletin describing how low-cost retro-commissioning at the Savannah River Site data centre cut cooling load and PUE.
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Overview
This bulletin was prepared for the US DOE Federal Energy Management Program (FEMP), with the primary author, Geoffrey Bell, from Lawrence Berkeley National Laboratory. Its subject is the low-cost retro-commissioning of the Savannah River Site data centre. The document dates from 2011 and is freely available. It shows with a concrete example how much can be gained by improving the settings and operating pattern of an existing system instead of investing in new equipment.
The measures included programming the electric reheat coils of the CRAH units off and turning off three CRAC units. Setpoints and airflow were also adjusted. These steps correspond to a common situation in legacy rooms: oversized cooling whose surplus units keep running unnecessarily, with reheat wasting energy. What these measures share is that they rely on the settings and operating pattern of the existing system and do not require buying new equipment.
The results are pronounced: total cooling system load dropped from 402.9 kW to 229.8 kW, a saving of 173.1 kW. PUE improved from 4.00 to 2.77, a 30% reduction in total electrical load. Total estimated savings were about 1,400,000 kWh per year for a total estimated cost of about $25,000. At $0.045/kWh, the simple payback was about 2.5 months. These figures come from the sidebar and results sections of the document.
The document is a case study of a single facility, so the results cannot be transferred directly to every room. A starting PUE of 4.00 shows the facility was quite inefficient at the outset, which explains the size of the gain. Even so, the bulletin shows that retro-commissioning of legacy rooms can be an investment that pays back quickly and deserves to be among the first steps evaluated.
Key points
- Total estimated savings were about 1,400,000 kWh per year for a total estimated cost of about $25,000.
- Simple payback was about 2.5 months at $0.045/kWh.
- Total cooling system load dropped from 402.9 kW to 229.8 kW (173.1 kW saving).
- PUE improved from 4.00 to 2.77, a 30% reduction in total electrical load.
- Measures included programming CRAH electric reheat coils off and turning off three CRAC units.
- Setpoints and airflow were also adjusted.
- The document is a FEMP bulletin with a primary author from LBNL, dated 2011.
- It is a single-facility case study; the results cannot be generalised directly.
Using it in design
- Add a retro-commissioning checklist to the commissioning module: reheat lockout, redundant unit staging and setpoint reset.
- Use this case as an example of oversized cooling in legacy rooms.
- Report the effect of measures as before and after values of cooling load (kW) and PUE.
- State the energy unit price explicitly in payback calculations; the case result rests on $0.045/kWh.
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Who should read it
Operations engineers, commissioning specialists and energy managers improving the efficiency of existing data centres.
Publication details
- Authors
- Geoffrey Bell
- Publisher
- U.S. DOE Federal Energy Management Program / Lawrence Berkeley National Laboratory
- Year
- 2011
- Document language
- English
- Source type
- Government / public
- Access
- Free to read
- Licence
- Copyright retained; citation only — the publisher’s terms apply to the original document
Original licence note
Prepared for DOE FEMP by a national-laboratory contractor (stated on cover); not US-Gov public domain. Cited only.
Citation
Geoffrey Bell (2011). Retro-Commissioning Increases Data Center Efficiency at Low Cost: Success at Savannah River Site (FEMP bulletin, 2011). U.S. DOE Federal Energy Management Program / Lawrence Berkeley National Laboratory. https://www.energy.gov/cmei/femp/articles/retro-commissioning-increases-data-center-efficiency-low-cost
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