...the 20-30[degrees]C range. Although there are many different perspectives for optimizing such a computing facility, ensuring device reliability by delivering uninterruptible power and cool air to the inlet of the electronics remains the most important goal. The objective of this paper is to compare two dominant airflow designs, namely, underfloor supply (raised floor) and overhead supply, with specific focus on the rack air inlet temperature. Numerical models of two data center sections, representing underfloor air supply and overhead air supply designs, were constructed utilizing commercial software, and the data generated from a parametric study were analyzed. The model constitutes a half-symmetry section of a 40-rack data center that is arranged in a cold aisle/hot aisle fashion. Temperature data were collected at several locations at the inlet to the racks. The effects of two different airflow designs (raised floor versus non-raised floor), supply airflow fraction, location of rack, and height of measurement were studied.

INTRODUCTION

Trends

The advances in semiconductor technology, combined with the packaging of microprocessors into formidable computing machines, have resulted in an explosive increase in the power consumed and heat dissipated by server racks for a given data center room footprint and volume. Data center equipment can house several hundred, sometimes several thousand, micro-processors. This has, in turn, posed a substantial burden on the air-conditioning infrastructure of the facility to ensure the delivery of cool air to the inlet of these devices. Thus, the cooling design of future data center facilities is a growing engineering challenge.

Figure 1a charts recent trends in rack heat load (ASHRAE 2005), showing the 2005 computer server rack heat fluxes to be in the 4000 W/[ft.sup.2] (43,056 W/[m.sup.2]) range, which translates to 27,000 W (92,132 Btu/h) for a 19 in. (0.483 m) rack. A 19 in. rack is one of the standard server racks with a footprint 24 in. (wide) x 40 in. (deep) (0.61 m x 1.016 m). A recent commercially available 19 in. (0.483 m) rack dissipates 32,000 W (109,194 Btu/h), which translates into a rack heat flux of 4800 W/[ft.sup.2] (52,000 W/[m.sup.2]). Figure 1b shows the measured values for average and hot spot high-density computing data center heat fluxes based on measurements carried out in the last three years by Schmidt and co-workers (Schmidt 2004; Schmidt et al. 2005, 2006). In one of the 2005 measurements, a server cluster test facility (Schmidt et al. 2006) showed extremely high hot spot heat fluxes of 720 W/[ft.sup.2] (7750 W/[m.sup.2]) over areas of 440 [ft.sup.2] (40.1 [m.sup.2]), or an 11 x 10 grid of tiles. The focus of this paper is on such ultra-high heat flux scenarios resulting from clusters of high heat load racks.

Air Distribution Configurations

Airflow distribution within a data center has a major impact on the thermal environment of the data processing equipment located within these rooms. A key requirement of manufacturers is that the inlet temperature and humidity to the electronic equipment be maintained within their specifications. To provide such a...

NOTE: All illustrations and photos have been removed from this article.



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