Impact of active tiles on data center flow and temperature distribution

Localized hot spots pose a major problem for data center thermal management. At present, most centers respond to hot spots by increasing the server fan speed to provide more cold air at the location of the hot spot. In an attempt to make sure that each server operates under temperature thresholds many servers are over-cooled. Thus, ensuring that cold air is available everywhere at all times requires over-provisioning the data center. Conversely, a lack of cold air causes recirculation of warm room air, making the hot spot worse. The desirable approach is instead to provide additional cold air only where and when required, and avoid overcooling the entire data center. Active tiles with integrated fans increase the local volume flowrate by redistributing the cold air supplied by the CRAC (computer room air conditioning) to the underfloor plenum. The objective of this work is to determine whether active tiles can be used to efficiently and economically eliminate hot spots in data centers. Experiments were conducted to determine air flow and temperature distributions, as a function of the CRAC unit blower and active tile fan speeds, for both a single tile/rack combination and a complete aisle populated with active tiles. The results were compared with those for passive (generic) tiles with similar effective porosity. Cross-correlation factors representing the effect of active tile on adjacent tiles are presented, and the power consumed by the active tiles in terms of W/m3 air at the tile outlet is compared with that for passive tiles. The results indicate that the power consumption per unit air flow can be reduced by using a full aisle of active tiles. Based on the experimental observations, a control framework that uses the active tile fan speed as a process variable to provide the air flowrate required to cool the hot spot, while reducing power consumption by the server fan, and hence the energy consumed by the data center can be designed.