ASHRAE Journal - January 2009 - (Page 38) mixed environments with a fairly uniform space temperature, Rating RCI this ambient made sense but not in today’s more organized Ideal 100% environments. Environmental specifications and sensor placeGood ≥96% ment should reflect the intake conditions. The flawed idea of Acceptable 91% – 95% ambient conditions has long hampered an organized approach Poor ≤90% of analyzing modern telecom switching centers. No Tool for Analyzing the Conditions. After realizing Table 1: Sugg ested RCI quality r atings using ASHRAE Class 1 environment. that the intake temperature is the important temperature for air-cooled equipment, an organized approach to thermal management finally emerged. GR-3028-CORE 2 was an important first step in that direction. It presented a cohesive and holistic picture of the thermal network environment; it spelled out the importance of harmony between equipment cooling and space cooling. It went on providing a framework for a common language, as well as estimating the maximum heat density in various typical network environments Figure 2: Point loads on perimeter aisle, lineup C (section view). by using computational fluid dynamics (CFD) modeling. Still, an effective tool was yet to emerge to compress unwieldy Several of the concepts developed in GR-3028-CORE were CFD (or measured) data. Although such modeling provides a subsequently used in Thermal Guidelines for Data Process- wealth of information, sorting things out is often a tremendous ing Environments.1 challenge. Figure 1 demonstrates the difficulties. Solutions So, how’s your view? Is business looking up at your company? Do you feel challenged and empowered to make a difference? A fulfilling, stimulating mechanical engineering career is possible. An exciting future for rising stars. www.meadhunt.com www.info.hotims.com/22183-124 Having discussed a few major limitations and issues, some effective solutions are needed for developing strategies dealing with point loads in existing network facilities. Metric for Analyzing the Conditions. Since the thermal network environment is defined by the equipment intake temperatures, compliance with intake specifications is the ultimate cooling performance metric. The Rack Cooling Index (RCI)4 metric has been adopted for the Data Center Assessment Protocol developed by Lawrence Berkeley National Laboratory for the U.S. Department of Energy (DOE). In the research, the cooling effectiveness was gauged by the RCI when point loads were introduced. By using CFD modeling in tandem with this metric, a tremendous amount of data could be processed and presented in an understandable, objective, and standardized way. The use of the RCI allowed the ideas from GR-3028-CORE to be further developed and refined. Other relevant applications of the RCI are outlined in Reference 5. Specifically, the RCIHI is a measure of the absence of overtemperatures. RCIHI = 100% mean ideal conditions; all intake temperatures are below the recommended maximum temperature (i.e., total absence of over-temperatures). The RCIHI is a quantitative measure of the equipment environment at the high end of the temperature range. Although an analogous index (RCILO) is defined at the low end, the RCIHI generally takes precedence. The definition of RCIHI is as follows (the calculation can easily be automated): January 2009 38 ASHRAE Journal http://www.meadhunt.com http://www.meadhunt.com http://www.info.hotims.com/22183-124
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