Ashrae Journal - October 2008 - (Page 38) 100% Power Consumption100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0% 20% 40% Load 60% In-Row Variable Unit Power 80% 100% Variable IT Load °F 85.1 – 90.0 80.1 – 85.0 75.1 – 80.0 70.1 – 75.0 65.1 – 70.0 60.1 – 65.0 55.1 – 60.0 55.0 Total J Hours ßJ 194 916 1,353 894 1,041 932 1,234 2,196 8,760 1 2 3 4 5 6 7 8 Figure 4: Variable speed fan electrical consumption. Note: Energy savings from variable airflow may not be recognized by all row-based cooling systems. This feature is specific to systems incorporating a variable speed control algorithm. Table 1: Condenser water bin hours. cooling tower fans shall be adjusted accordingly to the demand factor placed upon the chiller by the various cooling architectures considered. Table 2 establishes the performance of the central chiller in terms of kWh consumed versus kWh load. The particular chiller selected has exceptionally high part load and low lift efficiencies. This was a deliberate choice to avoid possible exaggeration of downstream efficiency gains between the various cooling architectures. Less efficient selections downstream of the air handler (chiller, pump, and cooling tower) will magnify overall power consumed by increased fan loads. Chiller power ratios (λ) with condenser water temperature greater than 85°F (29°C) have been extrapolated. Errors introduced by this method are minimal, as operating hours beyond this temperature account for only 3% of total hours. The chilled water circulating loop shall have a base loss of 40 ft (12 m) of head allowed for facility piping and chiller, and shall be summed with the air-handler losses for the specific cooling architectures. The chilled water flow rates shall be set at the value required for the specific cooling architecture. In-Row Air-Handler (IRAH) www.info.hotims.com/16018-44 As previously mentioned, an alternate method and emerging cooling architecture for IT loads is to intersperse airhandling units within rows containing racks housing the IT loads. Theses air handlers are designed for this application with special control algorithms to maximize the stability of the thermal environment. Typically, these air handlers are small, allowing nearly ideal capacity resolution versus IT loads. Additionally, placement within the IT 9/17/08 1:42:52 AM 38 A1 D55771asjl_810762.indd S H R A E Journal October 2008 http://www.pducables.com http://www.info.hotims.com/16018-44
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