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The speed at which data center technology changes and the significant power consumption essential to data center operations means that even a small percentage reduction in power consumption can reap thousands of dollars in savings. Savvy data center operators are realizing that retro-commissioning on a regular basis can find significant ways to improve overall data center operations and reduce energy costs simultaneously.
For example, in 2011, Lawrence Berkeley National Laboratory (LBL) assessed six Department of Defense (DOD) high-performance computing centers.
"Total potential annual energy savings were estimated at more than 8,000 megawatt hours (MWh)," explains Rod Mahdavi, PE, LEED AP, program manager, Environmental Energy Technologies Division of LBL.
Are such improvements tied to high price tags? Surprisingly, Mahdavi finds many have simple payback periods of less than two years. The DOD retro-commissioning analysis, for instance, can yield energy cost savings of approximately $1 million annually. That's an 8 percent energy savings with changes and improvements with an average payback period of less than two years, according to Mahdavi.
He says many retro-commissioned data centers actually benefit during the assessment process itself. Some elements identified during the retro-commissioning were executed in real time. This allowed energy use assessments and implementation of some of the energy efficiency measures to occur while the LBNL team was on-site.
For instance, one federal data center retro-commissioned by LBL during 2012 is now operating with 20 percent of its installed computer room air handling units (CRAHs) turned off.
"No considerable change in IT equipment air intake temperatures was observed by turning off the CRAH units," says Mahdavi. "Estimated annual saving was 530 MWh, or $32,000 annually."
Even new data centers can benefit from retro-commissioning. The National Oceanic and Atmospheric Administration's data center underwent an LBL energy efficiency measures (EEMs) assessment last year. The 6 megawatt capacity, high density data center began operating in October 2011.
The LBL retro-commissioning team found numerous savings options and grouped them into one of six "action packages." If NOAA implements all six packages across its high density data center, the result would be an investment of about $113,000 to achieve approximately 12 percent energy savings, explains Mahdavi. If all packages are done, total savings have a simple payback period of 1.4 years.
"Calculated with an estimated electricity cost of 6 cents per kilowatt-hour, savings of approximately $84,000 per year are possible," maintains Mahdavi.
Action packages include a low cost package, HVAC system retrofit/adjustment package, lighting retrofit/adjustment package, generator block heater package, controls upgrade of the dry cooler package, and a reset of the electrical room setpoint temperature.
For example, the low-cost action package is estimated to cost $25,500 and to yield about $25,000 in annual savings. The package suggests sealing floor and rack air leaks, installing hot aisle containment for the data storage room, making sure all server cabinets are facing in the right direction and are in the right location. This package also recommends raising the supply air temperature (SAT) setpoint or rack air intake setpoint to 80 degrees Fahrenheit and monitoring the temperature. Installation of differential pressure sensors above or below the floor would control air handling units (AHUs). Finally, AHU fan speed in the server room should be regulated by variable frequency drives and extra CRAHs in the data storage hall should be shut off. Mahdavi notes that these costs are only estimates; actual costs might be different.
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