Consulting-Specifying Engineer - March 2009 - (Page 13) M/E/P Roundtable leaving IT equipment running that isn’t necessarily processing data. There is not yet a comprehensive enough standard to support PUE comparison between different facilities and business entities. The new attention from the corporate energy czars on PUE results and metrics is contributing to an overall environmental improvement. But until the above factors are incorporated into the evolving standard, we all need to realize that PUE is better for demonstrating individual site characteristics and improvements than for comparing ourselves with others. Michael Ryan: What is great about this is that even though the methods are still being refined by the Green Grid, PUE has everyone looking at their data center operations differently than before. It has really brought a focus on how to reduce energy usage in the data center. Even the simplest PUE calculation can help you identify areas where your data center energy efficiency can be improved. CSE: For a recent new construction or retrofit project, describe some MEP measures that significantly improved PUE. Babigian: Occupancy sensors and high-efficiency lighting are two ways to improve PUE. Turning lights out in a large facility can save a great deal of money. Zoning sensors into pod areas ensures that large amounts of lighting are not needlessly burning. Other effective measures include: • Hot-aisle containment systems to reduce cold and hot air from mixing, along with blocking/blanking of raised floor openings • Installation of cabling overhead rather than under the floor to allow unrestricted airflow • Optimization of equipment layout using computational fluid dynamics Occupancy sensors and high-efficiency lighting are two ways to improve PUE. Turning lights out in a large facility can save a great deal of money. Zoning sensors into pod areas ensures that large amounts of lighting are not needlessly burning. —Peter Babigian (CFD) analysis to ensure that efficient airflow is achieved • When data center size and contiguous adjacent office space are coupled with a good balance, data center heat output can be used to warm office space. Lane: I’d add: • “Just right” sizing of electrical distribution equipment: Oversized electrical equipment and additional redundancy can provide for a system that is loaded to less than 50%. Transformers and UPS systems operate at lower efficiency at a level less than 50% loaded. More losses equal less efficiency and higher PUE. • Modular build-out of the electrical systems: Modular build-outs can ensure higher percent loading of the electrical equipment and a more efficient electrical system. • Outside air economizers with “free” cooling: Air handling units with evaporative coils are a very efficient method of cooling data centers and other critical environments. In cooler climates, the system can operate in this mode without a chiller a majority of the time. • Increase cold aisle temperatures: Increasing the allowable cold aisle temperatures to the high 70s F or low 80s F may allow the system to operate without a chiller. This can reduce the initial cost of the data center, and the size of the standby generators, while lowering PUE. Berry: Factors that have had the most significant impact on PUE in recent projects include the following: • Relaxation of environmental criteria in data halls and electrical plant rooms • Optimizing chilled water temperature to minimize system energy consumption (chiller power, chilled water pumping power, and computer room air conditioner (CRAC) unit fan power) • The use of water-cooled chillers with water-side free cooling • The use of actively controlled variable volume fans in CRAC units. Ryan: Most of the larger gains in PUE are typically found in the mechanical systems: • Outside air and airside economization should be used as much as is feasible to control server heat loads. • Extend room relative humidity percent ranges as wide as possible and base them on equipment manufacturers’ specs. • Specify all air handling equipment with variable speed drives to allow them to ramp back when room loads are less than design conditions. • Chilled water loops should be variable in all aspects using variable speed pumping systems, chillers, and cooling towers. • The chilled water loop temps should be as high as possible to increase economization use and include temperature resets based on load conditions. In the electrical systems, typically it is the UPS where the largest efficiency gains can be made. The UPS should be designed such that it operates efficiently across the full range of expected operation. A data center with redundant UPS system can run at 30% to 40% use. This can be a relatively low efficiency point on UPS systems, so proper system design and equipment selection can greatly reduce the losses that occur in the UPS. Lastly, a comprehensive monitoring and control system that integrates both building management systems and environmental monitoring systems into one package is a necessary tool for tracking and keeping a low PUE. Consulting-Specifying Engineer • MARCH 2009 13
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