DA-13-016 -- The Impact of Barometric Pressure, Temperature, and Operating Temperature Difference on Air-Cooled Data Centers PDF

This paper explores how barometric pressure, air temperature, and air temperature difference affect any sensible cooling process. In data centers, the equations presented apply to the heat rejection that occurs within air-cooled servers and airhandling units used to remove the heat from the building. In this paper the focus will be on the air handlers, however the same equations are applicable to the servers. The purpose of this paper is solely to bring together in one place some relevant equations, tables, and graphs that will assist engineers that are designing or evaluating sensible heat rejection systems. To be clear, the equations presented in this paper are applicable only when there is no moisture condensed in the cooling process

• A small change in air handler or server operating delta t ( t) from 20°F (11.1°C) to 22°F (12.2°C) results in a reduction of 9.1% in required cooling airflow for the respective air handler or server.
• Most cities experience normal drops in barometric pressure during the year equivalent to a 500 to 1000 ft (152.4 to 304.8 m) increase in altitude, resulting in the need for cooling air to increase by 2% to 3.5%.