IDENTIFYING THE ROOT CAUSE

One of the key benefits of computer simulation is its ability to help identify the cause of a problem. It can be used to understand why the cabinet located at the end of Row 1B was the only one to receive air above 20°C in the base case. In Figure 3, particle tracking is used to track the source of the air entering the front of the problem cabinet. The particles are colored to represent their temperatures. The simulation output shows how warm air from the backs of the cabinets reaches the front of the problem cabinet.

The first variant evaluated the effect on data-center cooling of eliminating one CRAC unit (Figure 4). This reduced the proportion of grilles operating within ±5 percent of the mean flow from 78 percent in the base case to 64 percent. The number of cabinets receiving air above 20°C increased from one to seven. This can be understood by observing pressure distribution in the void (Figure 5). With all of the 12 CRAC units operating, pressure distribution 0.2 m above the floor slab generally is uniform. With one CRAC out of operation, a greater pressure variation is seen, particularly near the failed unit.

EFFECT OF REDUCING FLOOR VOID

Figure 6 shows temperatures at the level of the equipment intake for the case in which the floor void is reduced to 0.5 m. The simulation output shows that the number of cabinets receiving air above 20°C has increased from one to five. Most of the cabinets receiving the hot air are toward the ends of rows, although one cabinet in the middle of Row 1B is receiving hot air. The amount of cool air leaking from the ends of the cold aisles also is reduced (Figure 7). The number of grilles with flow within ±5 percent of the mean has been reduced from 78 percent in the base case to 33 percent. The pressure distribution in the void shows an increase in nonuniformity.