Cooling High Density Racks in Your Data Center

Submitted by Wally Phelps - Engineering Manager with AdaptivCool, an EEC partner

Blade servers and other high density IT equipment is becoming more mainstream by the day. Data Centers and server rooms that were designed to cool 1-3KW racks are now being asked to house and cool racks of 10KW or more. Computer Room Air Conditioning (CRAC) capacity is often more than adequate, however distributing the additional cooling air required pushes sited and the new IT gear to the breaking point.

The root cause is twofold. On the supply side there is often not enough static pressure under the floor to allow even open grate style perforated tiles to flow enough air. Typical data center design is targeted at 0.1"wc of static pressure. Actual measurements on hundreds of existing data centers shows typical pressures of 0.02 to 0.05" wc; less than half of the design point. The causes of this low pressure are myriad, from unintended breaches in walls and support columns that go un-noticed to excess cable cutouts and simply too many perforated tiles. Underfloor obstructions also prevent static pressure from being evenly distributed as does CRAC placement that causes underfloor vortexes and low pressure from colliding air streams under floor.

On the return side, the hot air exhaust from these new high density servers must have an unimpeded low resistance path back to the CRACs; to be cooled and reprocessed. High density equipment ejects a much higher volume of warmer air than many data centers can cope with; causing other servers in the room to literally choke on the hot exhaust of its neighbors.

The solutions can often be relatively simple, such as blocking cable cutouts that waste precious cold air, adding blanking panels or moving racks to more ideal locations (when possible). Even with these measures however static pressure tends to still be much lower than design. A typical improvement in static pressure from closing cable cutouts is 20% which equates to static pressures of 0.03" to 0.06", still far below design point and not able to cope with high density racks.

A more effective solution that immediately solves poor cooling distribution is to use active airflow devices. These can be thermostatically controlled underfloor air movers that install quickly and unobtrusively under existing perforated tiles. These devices deliver up to 1200 CFM to supply racks of 10-12KW with more than adequate cooling air. Even at very low static pressures! Another solution is overhead return air movers that pull hot exhaust air up and away from neighboring racks and deliver it efficiently to CRAC intakes.

The solution for cooling high density IT equipment is simple. Provide enough cool air to the intake side and ensure the hot exhaust does not affect other racks.