Consulting-Specifying Engineer - January 2008 - (Page 46) Outdoor air in data centers Data centers require a delicate balance of energy use, temperature, and humidity. Adding fresh air may balance this equation. BY BILL KOSIK, PE, CEM B 46 uildings leak air. Sometimes this leakage actually can produce unintended favorable results such as providing additional ventilation air for occupants. However, this uncontrolled leakage typically will have a negative impact on indoor temperature and humidity, and must be accounted for in the design process. Engineers who design HVAC systems for data centers understand that computers require an environment in which temperature and humidity are maintained in accordance with the computer manufacturers’ recommendations, ASHRAE guidelines (“Thermal Guidelines for Data Processing Environments” developed by the Mission Critical Facilities Technical Committee 9.9), and the Telcordia Network EquipmentBuilding System requirements. Modern data center facilities typically are designed to provide air to the inlet of the computer equipment that ranges from 68 F to 77 F, and 40% to 55% RH. Since maintaining these temperature and humidity tolerances for 8,760 h/yr is very energy-intensive, much attention and research currently is aimed at HVAC system control strategies and system efficiencies to reduce energy usage. Other than standards related to fire resistance and brief mentions of minimizing moisture migration out of humidified areas, most of the current documentation on data center design does not address how the building envelope that surrounds the computers affects the temperature, humidity, and energy use. To address what role the envelope plays, the following questions need to be answered: Consulting-Specifying Engineer • JANUARY 2008
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